- What vitamin is good for bones
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- Is magnesium good for your bones?
What vitamin is good for bones
Osteoporosis is a long-term (chronic) bone disorder that causes your bones to become thin, weak and break easily. In osteoporosis your bones become fragile and fracture (break) easily, especially the bones in your hip, spine, and wrist. Other sites where broken bones occur include the ankle, leg, forearm, upper arm and ribs. These fractures typically occur after a minor trip, fall or similar incident. Your bone is living tissue that is constantly being broken down and replaced. Bones increase in size and mass during periods of growth in childhood and adolescence, reaching peak bone mass around age 30. The greater your peak bone mass, the longer you can delay serious bone loss with increasing age. Peak bone mass is determined largely by genetic factors, with contributions from nutrition, endocrine status, physical activity, and health during growth 1). Everyone should therefore consume adequate amounts of calcium and vitamin D throughout childhood, adolescence, and early adulthood.
Bone mass in older adults equals the peak bone mass achieved by age 18–25 minus the amount of bone subsequently lost 2). Osteoporosis occurs when the creation of new bone doesn’t keep up with the loss of old bone. Broken bones can occur in patients with either osteoporosis or osteopenia (low bone density). Once a fracture occurs the person is considered to be at much higher risk of another fracture. The operational definition of osteoporosis is based on the T-score for bone mineral density (BMD) assessed by dual energy x-ray absorptiometry (DEXA) at the femoral neck or spine and is defined as a value for BMD 2.5 standard deviation (SD) or more below the young female adult mean. World Health Organization (WHO) criteria define a normal T-score value as within 1 standard deviation (SD) of the mean BMD value in a healthy young adult. Secondary osteoporosis is due to the presence of underlying disease or medications, can also lead to low bone mass, resulting in increased risk of fractures 3). Osteoporosis is called a “silent” disease, because you may have bone loss for many years without any symptoms until you break a bone. Osteoporotic fractures can cause severe pain and lead to a significant decrease in quality of life, with increased morbidity, mortality, and disability 4). Osteoporotic fracture can make it harder to do daily tasks on your own, such as walking. Over 50 percent of postmenopausal white women will have an osteoporotic-related fracture, and only 33 percent of senior women who have a hip fracture will be able to return to independent living 5). In white men, the risk of an osteoporotic fracture is 20 percent, however, the one-year mortality in men who have a hip fracture is twice that of women. Black males and females have a decreased incidence of osteoporosis compared to white, however, those diagnosed with osteoporosis have similar fracture risks 6). The aging of the American population is expected to triple the number of osteoporotic fractures 7).
Anyone can develop osteoporosis, but it is more common in older women. Osteoporosis is caused by a decrease in bone density, which makes your bones more fragile and easily broken. Everyone’s bones become weaker as they age, but in some people this process happens too quickly. You are more likely to develop osteoporosis if you have risk factors for the disease. Some of the risk factors can be reduced through lifestyle changes or medications but others, such as your age, cannot be changed.
Research has identified common risk factors for developing osteoporosis. Your doctor should investigate these risk factors. This mainly applies to patients 50 years and over but can also apply to younger adults. A bone density scan is the most common test to help diagnose osteoporosis.
Risk factors that cannot be changed include:
- Being over 70 years of age. Your chances of getting osteoporosis increase as you get older.
- Being female. You have a greater chance of getting osteoporosis if you are a woman. Women have smaller bones than men and lose bone faster than men do because of hormone changes that happen after menopause.
- Having fallen in the past
- Your parents having had hip fractures. Having a close family member who has osteoporosis or has broken a bone may also increase your risk.
- Early menopause
- Ethnicity. White women and Asian women are most likely to get osteoporosis. Hispanic women and African American women are also at risk, but less so.
Risk factors that can be reduced include:
- Not being physically active. Not exercising and not being active for long periods of time can increase your chances of getting osteoporosis. Like muscles, bones become stronger and stay stronger with regular exercise.
- Low muscle mass and strength
- Low body weight (BMI below 20kg/m²). Being too thin makes you more likely to get osteoporosis.
- Smoking. Smoking cigarettes can keep your body from using the calcium in your diet. Also, women who smoke go through menopause earlier than those who don’t smoke. These things can increase your risk for osteoporosis.
- High alcohol intake. People who drink a lot are more likely to get osteoporosis.
- Not eating enough energy-rich foods or proteins.
- Getting too little calcium can increase your chances of getting osteoporosis. Not getting enough vitamin D can also increase your risk for the disease. Vitamin D is important because it helps the body use the calcium in your diet.
If you suffer from certain diseases, you are more likely to develop osteoporosis. These include:
- Hypogonadism or early menopause
- Diseases that cause bone loss, such as rheumatoid arthritis
- Hyperthyroidism or hyperparathyroidism
- Chronic liver or kidney disease
- Celiac disease and inflammatory bowel disease
- Cushing’s syndrome
- Certain types of cancer
- Anorexia nervosa
Some medications can also increase your risk of developing osteoporosis, including:
- Steroids also called glucocorticoids — when used for more than 3 months. Glucocortiocoids are given to people who have arthritis, asthma, and many other diseases.
- Anti-androgen therapy — drugs that block testosterone from working and which are sometimes used to treat prostate cancer
- Aromatase inhibitors — drugs that block oestrogen from being produced and working and which are sometimes used to treat or prevent ovarian or breast cancer
- Thyroid hormone replacement therapy — which can be a risk factor when used for too long
- Antidepressant medications — particularly medicines from the selective serotonin reuptake inhibitors (SSRIs) group
- Proton pump inhibitors (PPIs) — medicines which make your stomach less acidic
- Thiazolidinedione — a medicine sometimes used to treat type 2 diabetes
- Antipsychotic medications — some medicines used in mental illnesses such as schizophrenia
- Anti-epileptic medications — some medicines used to control epilepsy
Osteoporosis is a silent disease. You may not know you have osteoporosis until your symptoms are severe or until you break a bone. Signs and symptoms of osteoporosis include frequent broken bones or fractures, low back pain, loss of height over time or a hunched back. You may get shorter over time due to osteoporosis. The condition can cause your vertebrae (the bones in your spine) to collapse. These problems tend to occur after a lot of bone calcium has already been lost. A bone mineral density (BMD) test is the best way to check your bone health.
You cannot always avoid osteoporosis. However, there are some changes you can make to prevent or reduce your risk. These include regular exercise and eat a diet rich in calcium and vitamin D and not smoking. They help keep your bones healthy as you age. Fruits and vegetables also contribute other nutrients that are important for bone health. Some people may need to take nutritional supplements in order to get enough calcium and vitamin D. If needed, medicines can also help. It is also important to try to avoid falling down. Falls are the number one cause of fractures in older adults.
Table 1. Recommended calcium and vitamin D intakes
|Life-stage group||Calcium mg/day||Vitamin D (IU/day)|
|Infants 0 to 6 months||200||400|
|Infants 6 to 12 months||260||400|
|1 to 3 years old||700||600|
|4 to 8 years old||1000||600|
|9 to 13 years old||1300||600|
|14 to 18 years old||1300||600|
|19 to 30 years old||1000||600|
|31 to 50 years old||1000||600|
|51- to 70-year-old males||1000||600|
|51- to 70-year-old females||1200||600|
|>70 years old||1200||800|
|14 to 18 years old, pregnant/lactating||1300||600|
|19 to 50 years old, pregnant/lactating||1000||600|
Abbreviations: mg = milligrams; IU = International Units[Source 8) ]
Women 50 years of age and younger and men 70 years of age and younger should get 1,000 mg of calcium per day. Women older than 50 years of age and men older than 70 years of age should get 1,200 mg of calcium per day. Women who are post-menopausal may need 1,500 mg of calcium per day. It is best to get your calcium from food. Nonfat and low-fat dairy products are good sources of calcium. Other options include dried beans, salmon, spinach, and broccoli. If you don’t get enough calcium from the food you eat, your doctor may suggest taking a calcium supplement.
Most people need about 800 International Units (IU) of vitamin D each day. Vitamin D helps your body absorb calcium. You can get vitamin D from sunlight, food, and supplements. Good sources of vitamin D include egg yolks, saltwater fish, liver, and milk with vitamin D. Your skin makes vitamin D when it is exposed to sunlight. However, you should be careful of sun exposure. Too much can cause skin cancer. Your doctor can test your blood to measure your vitamin D level. If your vitamin D level is low, your doctor may suggest taking a supplement.
Regular exercise helps you build and keep strong bones. This is why it’s important to begin an active lifestyle at a young age. However, it’s never too late to start exercising. Ask your doctor for tips on how to exercise safely. Try to do a mix of strength training and weight-bearing exercises.
What causes osteoporosis?
There are two ways osteoporosis can occur. You can lose too much bone or your body cannot produce enough bone. Some people have both issues. When you’re young, your bones are dense and strong. Osteoporosis makes your bones brittle and breakable.
It is natural to lose some bone mass as you age. For most adults, this begins in their mid 20s. Other factors can increase your risk of osteoporosis. Some of these risk factors are out of your control. For others, you can take steps to reduce your risk. Talk to your doctor about your risk factors.
- Uncontrollable risk factors:
- Sex: Osteoporosis is more common in women than men.
- Age: The older you are, the greater your chance of having osteoporosis.
- Race: Caucasians and Asians are more likely to have osteoporosis.
- Genetics: Your risk of osteoporosis is higher if it runs in your family.
- Menopause: This period in a woman’s life causes physical and hormonal effects. For example, it lowers your estrogen. These changes can increase your risk of osteoporosis. Your risk is even higher if you have early menopause (before age 45).
- Body frame: People who have small, thin frames are more likely to develop osteoporosis.
- Health: Certain conditions, such as cancer or stroke, can lead to osteoporosis.
- Controllable risk factors:
- Lack of calcium and/or vitamin D.
- Inactive lifestyle or lack of exercise.
- Smoking or tobacco use.
- Alcohol abuse.
- Eating disorders, such as anorexia nervosa.
- Hormonal imbalances. Examples include low estrogen or testosterone and high thyroid levels.
- Long-term use of certain medicines. Examples include corticosteroids and proton pump inhibitors (PPIs). Corticosteroids treat inflammation, pain, and chronic conditions, such as asthma and rheumatoid arthritis. Proton pump inhibitors (PPIs) help reduce stomach acid. These medicines can make it hard for your body to absorb calcium and cause osteoporosis.
How do I know if I have osteoporosis?
Osteoporosis does not become clinically apparent until a fracture occurs and so is sometimes referred to as the “silent disease.” Since osteoporosis does not have any symptoms until a bone breaks, it is important to talk to your doctor about your bone health. If your doctor feels that you are at risk for osteoporosis, he or she may order a bone density test. A bone density test measures how strong – or dense – your bones are and whether you have osteoporosis. It can also tell you what your chances are of breaking a bone. Bone density tests are quick, safe, and painless.
Bones affected by osteoporosis may become so fragile that fractures occur spontaneously or as the result of:
- Minor falls, such as a fall from standing height that would not normally cause a break in a healthy bone.
- Normal stresses such as bending, lifting, or even coughing.
Two-thirds of vertebral fractures are painless, although patients may complain of the resulting stooped or hunched posture (kyphosis) and height loss. Typical findings in patients with painful vertebral fractures may include the following:
- The episode of acute pain may follow a fall or minor trauma.
- Pain is localized to a specific, identifiable, vertebral level in the midthoracic to lower thoracic or upper lumbar spine.
- The pain is described variably as sharp, nagging, or dull; movement may exacerbate pain; in some cases, pain radiates to the abdomen.
- Pain is often accompanied by paravertebral muscle spasms exacerbated by activity and decreased by lying supine.
- Patients often remain motionless in bed because of fear of exacerbating the pain.
- Acute pain usually resolves after 4-6 weeks; in the setting of multiple fractures with severe kyphosis, the pain may become chronic.
Patients who have sustained a hip fracture may experience the following:
- Pain in the groin, posterior buttock, anterior thigh, medial thigh, and/or medial knee during weight-bearing or attempted weight-bearing of the involved extremity
- Diminished hip range of motion (ROM), particularly internal rotation and flexion
- External rotation of the involved hip while in the resting position
How is osteoporosis diagnosed?
Contact your doctor if you have signs of osteoporosis or if it runs in your family. The American Academy of Family Physicians recommends that certain women be screened for osteoporosis. This includes women who are 65 years and older or have an equal or greater fracture risk. Your doctor can help you assess your fracture risk. Currently, the American Academy of Family Physicians does not recommend that men be screened for osteoporosis.
Bone mineral density (BMD) measurement is recommended in the following patients 9):
- Women age 65 years and older and men age 70 years and older, regardless of clinical risk factors
- Postmenopausal women and men above age 50–69, younger postmenopausal women and women in menopausal transition based on risk factor profile
- Postmenopausal women and men age 50 and older who have had an adult-age fracture, to diagnose and determine the degree of osteoporosis
- Adults with a condition (e.g., rheumatoid arthritis) or taking medication (e.g., glucocorticoids in a daily dose ≥5 mg prednisone or equivalent for ≥3 months) associated with low bone mass or bone loss
To diagnose osteoporosis, your doctor will do a bone density scan called a dual energy X-ray absorptiometry (DEXA) that uses low levels of X-rays to determine how many grams of calcium and other bone minerals are packed into a segment of your bones. This is a common test that measures your bone density. The scan often checks your hips, spine, and wrist. These are the most common places to have osteoporosis.
The American Academy of Family Physicians does not recommend that doctors use DEXA scans for women younger than 65 or men younger than 70 unless there are risk factors.
Baseline laboratory studies include the following:
- Complete blood count: May reveal anemia
- Serum chemistry levels: Usually normal in persons with primary osteoporosis
- Liver function tests
- Thyroid-stimulating hormone (TSH) level: Thyroid dysfunction has been associated with osteoporosis
- 25-Hydroxyvitamin D [25(OH)D] level: Vitamin D insufficiency can predispose to osteoporosis
- Serum protein electrophoresis: Multiple myeloma may be associated with osteoporosis
- 24-hour urine calcium/creatinine: Hypercalciuria may be associated with osteoporosis; further investigation with measurement of intact parathyroid hormone and urine pH may be indicated; hypocalciuria may indicate malabsorption, which should be further evaluated with a serum vitamin D measurement and consideration of testing for malabsorption syndromes such as celiac sprue
- Testosterone (total and/or free) and luteinizing hormone/follicle-stimulating hormone: Male hypogonadism is associated with osteoporosis
Treatment for osteoporosis starts with changes to your diet and lifestyle. You need to get enough calcium and vitamin D. Your doctor will want you to increase your physical activity. This helps to strengthen your bones and increase your bone mass. Examples of weight-bearing exercises include walking, jogging, and climbing steps. You also should stop smoking and limit alcohol.
If you’re at risk for falls, reduce your risk by getting rid of tripping hazards in your home. For example, remove rugs, avoid slick surfaces, and move electrical cords. You can install grab bars in certain places, such as your bathroom and shower. The bars can help you move around more easily and safely.
Maintaining a healthy weight can also help you manage osteoporosis. Stopping smoking and reducing your alcoholic consumption to just 2 standard drinks a day can improve your bone strength.
Treatment recommendations are often based on an estimate of your risk of breaking a bone in the next 10 years using information such as the bone density test. If your risk isn’t high, treatment might not include medication and might just focus instead on modifying risk factors for bone loss and falls.
Your doctor may prescribe medicine(s) to help treat osteoporosis. There are several types and forms.
- Biophosphonates. For both men and women at increased risk of fracture, the most widely prescribed osteoporosis medications are bisphosphonates. Biophosphonates help reduce your risk of breaks and fractures. It also increases bone density. It comes in oral (pill) form or intravenous (IV or injection) form. Side effects can include nausea, abdominal pain and heartburn-like symptoms. You may have irritation of the esophagus (the tube that connects your mouth and stomach). These are less likely to occur if the medicine is taken properly. Some people cannot take biophosphonates. This includes people who have kidney disease or low levels of calcium in their blood, and women who are pregnant or nursing. Examples of biophosphonates include:
- Alendronate (Binosto, Fosamax): This medicine is used to help prevent and treat osteoporosis. They help reduce your risk of fractures by decreasing the rate of bone loss. They are available in pill form. Their most common side effect is an upset stomach.
- Risedronate (Actonel, Atelvia): This medicine is used to help prevent and treat osteoporosis. They help reduce your risk of fractures by decreasing the rate of bone loss. They are available in pill form. Their most common side effect is an upset stomach.
- Ibandronate (Boniva): This medicine helps to slow bone loss and increase bone density. It is available as a pill or injection. You have 2 options for the pill. You can take it daily or monthly. For the injection, your doctor or nurse will give you a shot every 3 months. Side effects may include lower back or side pain, shortness of breath, tightness in your chest, and bloody or cloudy urine.
- Zoledronic acid (Reclast, Zometa). This medicine is given through IV once a year. Intravenous forms of bisphosphonates don’t cause stomach upset but can cause fever, headache and muscle aches for up to three days. It might be easier to schedule a quarterly or yearly injection than to remember to take a weekly or monthly pill, but it can be more costly to do so.
- Hormone-related therapy:
- Estrogen, especially when started soon after menopause, can help maintain bone density. However, estrogen therapy can increase the risk of blood clots, endometrial cancer, breast cancer and possibly heart disease. Therefore, estrogen is typically used for bone health in younger women or in women whose menopausal symptoms also require treatment.
- Raloxifene (Evista) is not a hormone, but it mimics estrogen’s beneficial effects on bone density in postmenopausal women, without some of the risks associated with estrogen. Taking this drug can reduce the risk of some types of breast cancer. Hot flashes are a common side effect. Raloxifene also may increase your risk of blood clots.
- In men, osteoporosis might be linked with a gradual age-related decline in testosterone levels. Testosterone replacement therapy can help improve symptoms of low testosterone, but osteoporosis medications have been better studied in men to treat osteoporosis and thus are recommended alone or in addition to testosterone.
- Bone-building medications: If you can’t tolerate the more common treatments for osteoporosis — or if they don’t work well enough — your doctor might suggest trying:
- Teriparatide (Forteo) is a synthetic form of parathyroid hormone (PTH) and it stimulates new bone growth. This medicine helps prevent and treat osteoporosis in women. It’s given by daily injection under the skin. You inject it in your thigh or stomach once a day. After two years of treatment with teriparatide, another osteoporosis drug is taken to maintain the new bone growth. Common side effects are nausea, stomach pain, headache, muscle weakness, fatigue, and loss of appetite.
- Abaloparatide (Tymlos) is another drug similar to parathyroid hormone. You can take it for only two years, which will be followed by another osteoporosis medication.
- Romosozumab (Evenity). This is the newest bone-building medication to treat osteoporosis. It is given as an injection every month at your doctor’s office. It is limited to one year of treatment, followed by other osteoporosis medications.
- Calcitonin. This is a hormone that helps slow down bone loss. It is available as an injection or nasal spray. Side effects of the injection include diarrhea, stomach pain, nausea, and vomiting. Side effects of the nose spray include headache and irritation of your nose lining.
- Monoclonal antibody medications: This drug is used when other drugs don’t work or if you can’t tolerate other treatment options. Denosumab (Prolia, Xgeva) increases your bone density. Compared with bisphosphonates, Denosumab produces similar or better bone density results and reduces the chance of all types of fractures. Denosumab is delivered via a shot under the skin every six months. It can be used by both women and men. Side effects can include lower calcium levels, skin rash, or pain in the arms and legs. If you take denosumab, you might have to continue to do so indefinitely. Recent research indicates there could be a high risk of spinal column fractures after stopping the drug.
- A very rare complication of bisphosphonates and denosumab is a break or crack in the middle of the thighbone.
- A second rare complication is delayed healing of the jawbone (osteonecrosis of the jaw). This can occur after an invasive dental procedure such as removing a tooth.
You should have a dental examination before starting these medications, and you should continue to take good care of your teeth and see your dentist regularly while on them. Make sure your dentist knows that you’re taking these medications.
Exercise is an important part of an osteoporosis treatment program. Exercise can strengthen your bones and muscles and decrease your risk of falling. Research shows that the best physical activities for bone health include strength training or resistance training, like lifting weights and weight bearing exercises (exercise done while on your feet so you bear your own weight) like brisk walking, jogging, tennis or volleyball. Because bone is living tissue, during childhood and adulthood, exercise can make bones stronger. However, for older adults, exercise no longer increases bone mass. Instead, regular exercise can help older adults:
- Build muscle mass and strength and improve coordination and balance. This can help lower your chance of falling.
- Improve daily function and delay loss of independence.
An exercise program for osteoporosis should include four components:
- Weight-bearing exercises force your body to work against gravity, which helps to strengthen bones. Examples include walking, climbing stairs, playing tennis, and dancing. Higher-impact activities strengthen bone more than lower-impact exercises, but only do what your fitness level allows.
- Muscle-strengthening exercises use weights or your body’s own resistance to work against gravity. Examples include lifting free weights, using a weight machine, working with resistance bands, and lifting your own body weight. Do these types of exercises at least twice a week.
- Balance exercises improve your ability to hold yourself upright and help prevent falls. Examples include tai chi and yoga. Perform balance exercises at least twice a week.
- Flexibility exercises keep your muscles limber and joints mobile. They include yoga and stretching. Try to stretch for at least five to 10 minutes after every workout. Hold each stretch for 10 to 30 seconds.
Exercises that help improve your balance are useful to help avoid falling over in the future. Examples of some exercises that can help you improve your balance are:
- Tai Chi
- standing with your feet close together
- standing on one leg
- walking backwards
Reducing your likelihood of falling is also important. Consider how you might arrange your home and workplace so you are less likely to trip — for example by fixing down rugs and keeping the floor clear. Wearing sensible shoes and glasses if you need them can also help to keep you stable as your move around.
Although exercise is beneficial for people with osteoporosis, it should not put any sudden or excessive strain on your bones. If you have osteoporosis, you should avoid high-impact exercise. Your doctor or physiotherapist can help you build a safe exercise plan which suits your needs and reduces your risk of fracturing your bones. To help prevent injury and fractures, a physical therapist or rehabilitation medicine specialist can:
- Recommend specific exercises to strengthen and support your back.
- Teach you safe ways of moving and carrying out daily activities.
- Recommend an exercise program that is tailored to your circumstances.
Exercise specialists, such as exercise physiologists, may also help you develop a safe and effective exercise program.
Calcium is the most abundant mineral in your body, found in some foods, added to others, available as a dietary supplement, and present in some medicines (such as antacids). Almost all calcium is stored in your bones and teeth, where it supports their structure and hardness. Your body needs calcium to maintain strong bones and to carry out many important functions. Calcium is required for muscles to move and for nerves to carry messages between the brain and every body part. In addition, calcium is used to help blood vessels move blood throughout the body and to help release hormones and enzymes that affect almost every function in the human body, though less than 1% of total body calcium is needed to support these critical metabolic functions 10). Serum calcium is very tightly regulated and does not fluctuate with changes in dietary intakes; the body uses bone tissue as a reservoir for, and source of calcium, to maintain constant concentrations of calcium in blood, muscle, and intercellular fluids 11). The remaining 99% of your body’s calcium supply is stored in the bones and teeth where it supports their structure and function 12). Bone itself undergoes continuous remodeling, with constant resorption and deposition of calcium into new bone. The balance between bone resorption and deposition changes with age. Bone formation exceeds resorption in periods of growth in children and adolescents, whereas in early and middle adulthood both processes are relatively equal. In aging adults, particularly among postmenopausal women, bone breakdown exceeds formation, resulting in bone loss that increases the risk of osteoporosis over time 13).
The amount of calcium you need each day depends on your age. Average daily recommended amounts are listed below in milligrams (mg). The Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies established Recommended Dietary Allowances (RDAs) for the amounts of calcium required for bone health and to maintain adequate rates of calcium retention in healthy people. They are listed in Table 2 in milligrams (mg) per day.
Your body gets the calcium it needs in two ways. One is by eating foods or supplements that contain calcium. Good sources include dairy products, which have the highest concentration per serving of highly absorbable calcium, and dark leafy greens or dried beans, which have varying amounts of absorbable calcium. Calcium supplements often contain vitamin D; taking calcium paired with vitamin D seems to be more beneficial for bone health than taking calcium alone 14).
The other way the body gets calcium is by pulling it from bones. This happens when blood levels of calcium drop too low, usually when it’s been awhile since having eaten a meal containing calcium. Ideally, the calcium that is “borrowed” from the bones will be replaced at a later point. But, this doesn’t always happen. Most important, this payback can’t be accomplished simply by eating more calcium 15).
Not all calcium consumed is actually absorbed in the gut. Humans absorb about 30% of the calcium in foods, but this varies depending upon the type of food consumed 16). Other factors also affect calcium absorption including the following:
- Amount consumed: the efficiency of absorption decreases as calcium intake increases 17).
- Age and life stage: net calcium absorption is as high as 60% in infants and young children, who need substantial amounts of the mineral to build bone 18). Absorption decreases to 15%–20% in adulthood (though it is increased during pregnancy) and continues to decrease as people age; compared with younger adults, recommended calcium intakes are higher for females older than 50 years and for both males and females older than 70 years 19).
- Vitamin D intake: this nutrient, obtained from food and produced by skin when exposed to sunlight of sufficient intensity, improves calcium absorption 20).
- Other components in food: phytic acid and oxalic acid, found naturally in some plants, bind to calcium and can inhibit its absorption. Foods with high levels of oxalic acid include spinach, collard greens, sweet potatoes, rhubarb, and beans. Among the foods high in phytic acid are fiber-containing whole-grain products and wheat bran, beans, seeds, nuts, and soy isolates 21). The extent to which these compounds affect calcium absorption varies. Research shows, for example, that eating spinach and milk at the same time reduces absorption of the calcium in milk 22). In contrast, wheat products (with the exception of wheat bran) do not appear to lower calcium absorption 23). For people who eat a variety of foods, these interactions probably have little or no nutritional consequence and, furthermore, are accounted for in the overall calcium DRIs, which factor in differences in absorption of calcium in mixed diets.
Some absorbed calcium is eliminated from the body in urine, feces, and sweat. This amount is affected by such factors as the following:
- Sodium (salt) and protein intakes: high sodium intake increases urinary calcium excretion 24). High protein intake also increases calcium excretion and was therefore thought to negatively affect calcium status 25). However, more recent research suggests that high protein intake also increases intestinal calcium absorption, effectively offsetting its effect on calcium excretion, so whole body calcium retention remains unchanged 26).
- Caffeine intake: this stimulant in coffee and tea can modestly increase calcium excretion and reduce absorption 27). One cup of regular brewed coffee, for example, causes a loss of only 2–3 mg of calcium 28). Moderate caffeine consumption (1 cup of coffee or 2 cups of tea per day) in young women has no negative effects on bone 29).
- Alcohol intake: alcohol intake can affect calcium status by reducing its absorption 30) and by inhibiting enzymes in the liver that help convert vitamin D to its active form 31). However, the amount of alcohol required to affect calcium status and whether moderate alcohol consumption is helpful or harmful to bone is unknown.
- Phosphorus intake: the effect of this mineral on calcium excretion is minimal. Several observational studies suggest that consumption of carbonated soft drinks with high levels of phosphate is associated with reduced bone mass and increased fracture risk. However, the effect is probably due to replacing milk with soda rather than the phosphorus itself 32).
- Fruit and vegetable intakes: metabolic acids produced by diets high in protein and cereal grains increase calcium excretion 33). Fruits and vegetables, when metabolized, shift the acid/base balance of the body towards the alkaline by producing bicarbonate, which reduces calcium excretion. However, it is unclear if consuming more fruits and vegetables affects bone mineral density. These foods, in addition to reducing calcium excretion, could possibly reduce calcium absorption from the gut and therefore have no net effect on calcium balance.
It is important to get plenty of calcium in the foods you eat. Foods rich in calcium include:
- Dairy products such as milk, cheese, and yogurt
- Leafy, green vegetables
- Fish with soft bones that you eat, such as canned sardines and salmon
- Calcium-enriched foods such as breakfast cereals, fruit juices, soy and rice drinks, and tofu. Check the product labels.
The exact amount of calcium you need depends on your age and other factors. Growing children and teenagers need more calcium than young adults. Older women need plenty of calcium to prevent osteoporosis. People who do not eat enough high-calcium foods should take a calcium supplement.
Table 2. Recommended Dietary Allowances (RDAs) for Calcium
|0–6 months*||200 mg||200 mg|
|7–12 months*||260 mg||260 mg|
|1–3 years||700 mg||700 mg|
|4–8 years||1,000 mg||1,000 mg|
|9–13 years||1,300 mg||1,300 mg|
|14–18 years||1,300 mg||1,300 mg||1,300 mg||1,300 mg|
|19–50 years||1,000 mg||1,000 mg||1,000 mg||1,000 mg|
|51–70 years||1,000 mg||1,200 mg|
|71+ years||1,200 mg||1,200 mg|
Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.
* Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an Recommended Dietary Allowance (RDA).[Source 34) ]
Calcium Rich Foods
Calcium is found in many foods. You can get recommended amounts of calcium by eating a variety of foods, including the following:
- Milk, yogurt, and cheese are the main food sources of calcium for the majority of people in the United States.
- Kale, broccoli, and Chinese cabbage are fine vegetable sources of calcium.
- Fish with soft bones that you eat, such as canned sardines and salmon, are fine animal sources of calcium.
- Most grains (such as breads, pastas, and unfortified cereals), while not rich in calcium, add significant amounts of calcium to the diet because people eat them often or in large amounts.
- Calcium is added to some breakfast cereals, fruit juices, soy and rice beverages, and tofu. To find out whether these foods have calcium, check the product labels.
The U.S. Department of Agriculture’s (USDA’s) Nutrient Database website (https://fdc.nal.usda.gov) lists the nutrient content of many foods with Calcium arranged by nutrient content (https://ods.od.nih.gov/pubs/usdandb/Calcium-Content.pdf) and by food name (https://ods.od.nih.gov/pubs/usdandb/Calcium-Food.pdf).
Milk, yogurt, and cheese are rich natural sources of calcium and are the major food contributors of this nutrient to people in the United States 35). Nondairy sources include vegetables, such as Chinese cabbage, kale, and broccoli. Spinach provides calcium, but its bioavailability is poor. Most grains do not have high amounts of calcium unless they are fortified; however, they contribute calcium to the diet because they contain small amounts of calcium and people consume them frequently. Foods fortified with calcium include many fruit juices and drinks, tofu, and cereals. Selected food sources of calcium are listed in Table 3.
In its food guidance system, MyPlate, the U.S. Department of Agriculture recommends that persons aged 9 years and older eat 3 cups of foods from the milk group per day 36). A cup is equal to 1 cup (8 ounces) of milk, 1 cup of yogurt, 1.5 ounces of natural cheese (such as Cheddar), or 2 ounces of processed cheese (such as American).
Table 3. Selected Food Sources of Calcium
|Yogurt, plain, low fat, 8 ounces||415||32|
|Orange juice, calcium fortified, 1 cup||349||27|
|Mozzarella, part skim, 1.5 ounces||333||26|
|Sardines, canned in oil, with bones, 3 ounces||325||25|
|Cheddar cheese, 1.5 ounces||307||24|
|Milk, nonfat, 1 cup**||299||23|
|Soymilk, calcium fortified, 1 cup||299||23|
|Milk, reduced fat (2% milk fat), 1 cup||293||23|
|Milk, buttermilk, lowfat, 1 cup||284||22|
|Milk, whole (3.25% milk fat), 1 cup||276||21|
|Yogurt, fruit, low fat, 6 ounces||258||20|
|Tofu, firm, made with calcium sulfate, ½ cup***||253||19|
|Salmon, pink, canned, solids with bone, 3 ounces||181||14|
|Cottage cheese, 1% milk fat, 1 cup||138||11|
|Tofu, soft, made with calcium sulfate, ½ cup***||138||11|
|Breakfast cereals, fortified with 10% of the DV for calcium, 1 serving||130||10|
|Frozen yogurt, vanilla, soft serve, ½ cup||103||8|
|Turnip greens, fresh, boiled, ½ cup||99||8|
|Kale, fresh, cooked, 1 cup||94||7|
|Ice cream, vanilla, ½ cup||84||6|
|Chia seeds, 1 tablespoon||76||6|
|Chinese cabbage (bok choi), raw, shredded, 1 cup||74||6|
|Bread, white, 1 slice||73||6|
|Tortilla, corn, one, 6” diameter||46||4|
|Tortilla, flour, one, 6” diameter||32||2|
|Sour cream, reduced fat, 2 tablespoons||31||2|
|Bread, whole-wheat, 1 slice||30||2|
|Kale, raw, chopped, 1 cup||24||2|
|Broccoli, raw, ½ cup||21||2|
|Cream cheese, regular, 1 tablespoon||14||1|
Footnote: * DV = Daily Value. DVs were developed by the U.S. Food and Drug Administration to help consumers compare the nutrient contents among products within the context of a total daily diet. The DV for calcium is 1,000 mg for adults and children aged 4 years and older. Foods providing 20% of more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.[Source 37)]
It is best to obtain calcium from your diet. However when adequate calcium intake is not possible a supplement may be required as directed by your doctor or pharmacist. The two main forms of calcium in supplements are calcium carbonate and calcium citrate. Calcium carbonate is more commonly available and is both inexpensive and convenient 38). Due to its dependence on stomach acid for absorption, calcium carbonate is absorbed most efficiently when taken with food, whereas calcium citrate is absorbed equally well when taken with or without food 39). Calcium citrate is also useful for people with achlorhydria, inflammatory bowel disease, or absorption disorders 40). Other calcium forms in supplements or fortified foods include gluconate, lactate, and phosphate. Calcium citrate malate is a well-absorbed form of calcium found in some fortified juices 41). Calcium supplements are available as oral tablets, effervescent tablets or soluble powder.
Calcium supplements contain varying amounts of elemental calcium. For example, calcium carbonate is 40% calcium by weight, whereas calcium citrate is 21% calcium. Fortunately, elemental calcium is listed in the Supplement Facts panel, so consumers do not need to calculate the amount of calcium supplied by various forms of calcium supplements.
The percentage of calcium absorbed depends on the total amount of elemental calcium consumed at one time; as the amount increases, the percentage absorption decreases. Absorption is highest in doses ≤500 mg 42). So, for example, one who takes 1,000 mg/day of calcium from supplements might split the dose and take 500 mg at two separate times during the day.
Some individuals who take calcium supplements might experience gastrointestinal side effects including gas, bloating, constipation, or a combination of these symptoms. Calcium carbonate appears to cause more of these side effects than calcium citrate 43), so consideration of the form of calcium supplement is warranted if these side effects are reported. Other strategies to alleviate symptoms include spreading out the calcium dose throughout the day and/or taking the supplement with meals.
Calcium supplements are sometimes combined with vitamin D, as adequate vitamin D levels are important to assist the absorption of calcium in the body. Take supplements as directed and talk to your doctor or pharmacist if you have any queries.
Calcium phosphate supplement
The beneficial effects of calcium phosphate mainly focus on the intestinal metabolism, e.g., bile acid metabolism, fatty acid (cholesterol) excretion, and modulation of the gut microbiota 44), 45), 46), 47). Calcium from tricalcium phosphate (CaP, a water-insoluble compound at neutral pH value), is partly absorbed in the human gut; but the main part of the calcium and phosphorus is precipitated to amorphous calcium phosphate in the gut, and thus, not absorbed 48). Nevertheless, supplementation with vitamin D3 and calcium reduces the risk of hip fractures and other nonvertebral fractures among elderly women 49). Supplementation with daily 10 μg vitamin D3 significantly increases plasma 25-(OH)D concentration. The combination with daily 1 g calcium (as CaP) has a further increasing effect on the 25-(OH)D concentration. Both CaP alone and in combination with vitamin D3 have no beneficial effect on bone remodelling markers and on the metabolism of calcium, phosphorus, magnesium and iron 50).
Is it safe to take calcium supplements?
For most people, it is safe to eat foods containing calcium and to take calcium supplements that together do not exceed the tolerable upper intake level of 2.5 grams of calcium per day 51). This upper level for daily calcium intake in adults is the highest level that likely will not pose risks of unwanted side effects in the general population. The upper level of 2.5 grams a day is an average recommendation for all healthy people who are older than a year, regardless of gender 52).
Excessively high levels of calcium in the blood known as hypercalcemia can cause renal insufficiency, vascular and soft tissue calcification, hypercalciuria (high levels of calcium in the urine) and kidney stones 53). Although very high calcium intakes have the potential to cause hypercalcemia 54), it is most commonly associated with primary hyperparathyroidism or malignancy 55).
High calcium intake can cause constipation 56). It might also interfere with the absorption of iron and zinc, though this effect is not well established 57). High intake of calcium from supplements, but not foods, has been associated with increased risk of kidney stones 58).
Consuming too much calcium—in excess of 5 grams a day, or 3 grams a day in people with existing kidney problems 59) can lead to several harmful side effects. The milk-alkali syndrome, a triad of hypercalcemia, metabolic alkalosis, and renal insufficiency, was identified in 1923 as an adverse effect of peptic ulcer disease therapies involving the use of dairy products and alkaline powders 60). Most of these side effects result from people taking too many calcium supplements. Recent trends in the prevention and treatment of osteoporosis using widely available over-the-counter (OTC) calcium supplements appear to be contributing to its return 61). Rare harmful side effects from excess calcium include kidney stones 62), hypercalcemia (too much calcium in the blood), and kidney failure 63). In addition, excessive consumption of milk (which is high in calcium) and some types of antacids, especially antacids containing calcium carbonate or sodium bicarbonate (baking soda), over a long period of time can cause milk-alkali syndrome, a condition that can also lead to calcium deposits in the kidneys and other tissues and to kidney failure 64), 65), 66).
Some evidence links higher calcium intake with increased risk of prostate cancer, but this effect is not well understood, in part because it is challenging to separate the potential effect of dairy products from that of calcium 67). Some studies also link high calcium intake, particularly from supplements, with increased risk of cardiovascular disease 68), 69).
The Tolerable Upper Intake Levels (ULs) for calcium established by the Food and Nutrition Board are listed in Table 4 in milligrams (mg) per day. Getting too much calcium from foods is rare; excess intakes are more likely to be caused by the use of calcium supplements. National Health and Nutrition Examination Survey (NHANES) data from 2003–2006 indicate that approximately 5% of women older than 50 years have estimated total calcium intakes (from foods and supplements) that exceed the UL by about 300–365 mg 70).
Table 4. Tolerable Upper Intake Levels (ULs) for Calcium
|0–6 months||1,000 mg||1,000 mg|
|7–12 months||1,500 mg||1,500 mg|
|1–8 years||2,500 mg||2,500 mg|
|9–18 years||3,000 mg||3,000 mg||3,000 mg||3,000 mg|
|19–50 years||2,500 mg||2,500 mg||2,500 mg||2,500 mg|
|51+ years||2,000 mg||2,000 mg|
How does your body control blood calcium levels?
Normally, your body controls blood calcium by adjusting the levels of several hormones. When blood calcium levels are low, your parathyroid glands (four pea-sized glands in your neck) secrete a hormone called parathyroid hormone (PTH). PTH helps your bones release calcium into the blood.
Vitamin D is also important in keeping calcium levels in the normal range. Vitamin D, which is actually a hormone, helps your body absorb calcium and move it from your intestines into your blood.
Together, PTH and vitamin D, along with other hormones and minerals, help move calcium in or out of body tissues to keep your blood calcium at a normal level.
The regulation of both calcium and phosphate balance is greatly influenced by concentrations of circulating parathyroid hormone (PTH), vitamin D, and, to a lesser extent, calcitonin. Calcium and phosphate concentrations are also linked by their ability to chemically react to form calcium phosphate. The product of concentrations of calcium and phosphate (in mEq/L) is estimated to be < 60 normally; when the product exceeds 70, precipitation of calcium phosphate crystals in soft tissue is much more likely. Calcification of vascular tissue accelerates arteriosclerotic vascular disease and may occur when the calcium and phosphate product is even lower (> 55), especially in patients with chronic kidney disease.
Calcium is absorbed passively (no cellular energy required) in the intestines by diffusing through the spaces between cells. It is also absorbed actively (cellular energy required) through intestinal cells by binding to a transport protein known as calbindin. The production of calbindin is dependent on vitamin D 71).
Not all calcium consumed is actually absorbed in the gut. Humans absorb about 30% of the calcium in foods, but this varies depending upon the type of food consumed 72). Other factors also affect calcium absorption including the following:
- Amount consumed: the efficiency of absorption decreases as calcium intake increases 73).
- Age and life stage: net calcium absorption is as high as 60% in infants and young children, who need substantial amounts of the mineral to build bone 74). Absorption decreases to 15%–20% in adulthood (though it is increased during pregnancy) and continues to decrease as people age; compared with younger adults, recommended calcium intakes are higher for females older than 50 years and for both males and females older than 70 years 75).
- Vitamin D intake: this nutrient, obtained from food and produced by skin when exposed to sunlight of sufficient intensity, improves calcium absorption 76).
- Other components in food: phytic acid and oxalic acid, found naturally in some plants, bind to calcium and can inhibit its absorption. Foods with high levels of oxalic acid include spinach, collard greens, sweet potatoes, rhubarb, and beans. Among the foods high in phytic acid are fiber-containing whole-grain products and wheat bran, beans, seeds, nuts, and soy isolates 77). The extent to which these compounds affect calcium absorption varies. Research shows, for example, that eating spinach and milk at the same time reduces absorption of the calcium in milk 78). In contrast, wheat products (with the exception of wheat bran) do not appear to lower calcium absorption 79). For people who eat a variety of foods, these interactions probably have little or no nutritional consequence and, furthermore, are accounted for in the overall calcium Dietary Reference Intakes (DRIs), which factor in differences in absorption of calcium in mixed diets.
Some absorbed calcium is eliminated from the body in urine, feces, and sweat. This amount is affected by such factors as the following:
- Sodium (salt) and protein intakes: high sodium intake increases urinary calcium excretion 80). High protein intake also increases calcium excretion and was therefore thought to negatively affect calcium status 81). However, more recent research suggests that high protein intake also increases intestinal calcium absorption, effectively offsetting its effect on calcium excretion, so whole body calcium retention remains unchanged 82).
- Caffeine intake: this stimulant in coffee and tea can modestly increase calcium excretion and reduce absorption 83). One cup of regular brewed coffee, for example, causes a loss of only 2–3 mg of calcium 84). Moderate caffeine consumption (1 cup of coffee or 2 cups of tea per day) in young women has no negative effects on bone 85).
- Alcohol intake: alcohol intake can affect calcium status by reducing its absorption 86) and by inhibiting enzymes in the liver that help convert vitamin D to its active form 87). However, the amount of alcohol required to affect calcium status and whether moderate alcohol consumption is helpful or harmful to bone is unknown.
- Phosphorus intake: the effect of this mineral on calcium excretion is minimal. Several observational studies suggest that consumption of carbonated soft drinks with high levels of phosphate is associated with reduced bone mass and increased fracture risk. However, the effect is probably due to replacing milk with soda rather than the phosphorus itself 88).
- Fruit and vegetable intakes: metabolic acids produced by diets high in protein and cereal grains increase calcium excretion 89). Fruits and vegetables, when metabolized, shift the acid/base balance of the body towards the alkaline by producing bicarbonate, which reduces calcium excretion. However, it is unclear if consuming more fruits and vegetables affects bone mineral density. These foods, in addition to reducing calcium excretion, could possibly reduce calcium absorption from the gut and therefore have no net effect on calcium balance.
Parathyroid hormone (PTH) is secreted by the parathyroid glands. It has several actions, but perhaps the most important is to defend against hypocalcemia. Parathyroid cells sense decreases in serum calcium and, in response, release preformed PTH into the circulation. PTH increases serum calcium within minutes by increasing renal and intestinal absorption of calcium and by rapidly mobilizing calcium and phosphate from bone (bone resorption). Renal calcium excretion generally parallels sodium excretion and is influenced by many of the same factors that govern sodium transport in the proximal tubule. However, PTH enhances distal tubular calcium reabsorption independently of sodium.
PTH also decreases renal phosphate reabsorption and thus increases renal phosphate losses. Renal phosphate loss prevents the solubility product of calcium and phosphate from being exceeded in plasma as calcium concentrations rise in response to PTH.
PTH also increases serum calcium by stimulating conversion of vitamin D to its most active form, calcitriol. This form of vitamin D increases the percentage of dietary calcium absorbed by the intestine. Despite increased calcium absorption, long-term increases in PTH secretion generally result in further bone resorption by inhibiting osteoblastic function and promoting osteoclastic activity. PTH and vitamin D both function as important regulators of bone growth and bone remodeling (see Vitamin D Deficiency and Dependency).
Radioimmunoassays for the intact PTH molecule are still the recommended way to test for PTH. Second-generation assays for intact PTH are available. These tests measure bioavailable PTH or complete PTH. They give values equal to 50 to 60% of those obtained with the older assay. Both types of assays can be used for diagnosing primary hyperparathyroidism or monitoring hyperparathyroidism secondary to renal disease, as long as normal ranges are noted.
PTH increases urinary cAMP. Sometimes total or nephrogenous cAMP excretion is measured in diagnosis of pseudohypoparathyroidism.
Calcitoninis secreted by the thyroid parafollicular cells (C cells). Calcitonin tends to lower serum calcium concentration by enhancing cellular uptake, renal excretion, and bone formation. The effects of calcitonin on bone metabolism are much weaker than those of either PTH or vitamin D.
Vitamin D also called Calciferol, is a fat-soluble vitamin that is naturally present in very few foods, added to others, and available as a dietary supplement. In foods and dietary supplements, vitamin D has two main forms, vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol), that differ chemically only in their side-chain structures. Both forms are well absorbed in the small intestine. Absorption occurs by simple passive diffusion and by a mechanism that involves intestinal membrane carrier proteins 90). The concurrent presence of fat in the gut enhances vitamin D absorption, but some vitamin D is absorbed even without dietary fat. Neither aging nor obesity alters vitamin D absorption from the gut 91). Vitamin D is also produced endogenously when ultraviolet rays from sunlight strike your skin and trigger vitamin D synthesis. The major source of vitamin D is sunlight. Vitamin D deficiency is typically due to limited sunlight exposure. Vitamin D obtained from sun exposure, food, and supplements is biologically inert and must undergo two hydroxylations in the body for activation 92). The first occurs in the liver and converts vitamin D to 25-hydroxyvitamin D [25(OH)D], also known as calcidiol or 25-hydroxyvitamin D3 (25-hydroxycholecalciferol). The second occurs primarily in the kidney and forms the physiologically active 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol 93). All forms of vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) obtained from your diet or from supplements require conversion in your liver and kidneys before being active in your body. A manufactured calcitriol or vitamin D3 is used to treat kidney disease with low blood calcium, hyperparathyroidism due to kidney disease, low blood calcium due to hypoparathyroidism, osteoporosis, osteomalacia, and familial hypophosphatemia. It is taken by mouth or by injection into a vein.
Sunlight exposure is the primary source of vitamin D for most people. Solar ultraviolet-B radiation (UVB; wavelengths of 290 to 315 nanometers) stimulates the production of vitamin D3 from 7-dehydrocholesterol in the epidermis of the skin. Hence, vitamin D is actually more like a hormone than a vitamin, a substance that is required from the diet. Vitamin D3 enters the circulation and is transported to the liver, where it is hydroxylated to form 25-hydroxyvitamin D3 (calcidiol; the major circulating form of vitamin D). In the kidneys, the 1-α-hydroxylase enzyme catalyzes a second hydroxylation of 25-hydroxyvitamin D3, resulting in the formation of 1,25-dihydroxyvitamin D3 [calcitriol, 1,25-dihydroxyvitamin D3 or vitamin D3] — the most potent form of vitamin D 94). Most of the physiological effects of vitamin D in the body are related to the activity of 1,25-dihydroxyvitamin D3 (also known as calcitriol or vitamin D3). Keratinocytes in the epidermis possess hydroxylase enzymes that locally convert vitamin D to 1,25-dihydroxyvitamin D3, the form that regulates epidermal proliferation and differentiation 95).
Figure 1. Production of vitamin D3 in the skin
The plasma calcitriol (1,25-dihydroxyvitamin D or 1,25(OH)2D) or vitamin D concentration depends on the availability of calcidiol (25-hydroxyvitamin D or 25(OH)D) and the activities of the renal enzymes 1-α-hydroxylase and 24-α-hydroxylase 96). The renal 1-α-hydroxylase enzyme is primarily regulated by parathyroid hormone (PTH), serum calcium and phosphate concentrations, and fibroblast growth factor 23 (FGF23) 97). Increased parathyroid hormone (PTH), calcitonin, and hypophosphatemia (low blood phosphate) stimulate the renal enzymes 1-α-hydroxylase and enhance calcitriol [1,25(OH)2D] production, while high calcium, hyperphosphatemia (high blood phosphate) and calcitriol [1,25(OH)2D] inhibit the renal enzymes 1-α-hydroxylase 98). Calcitriol [1,25-dihydroxyvitamin D or 1,25(OH)2D] inhibits the synthesis and secretion of parathyroid hormone (PTH), providing negative feedback regulation of calcitriol production. Calcitriol [1,25-dihydroxyvitamin D or 1,25(OH)2D] synthesis may also be modulated by vitamin D receptors on the cell surface; downregulation of these receptors may play an important role in regulating vitamin D activation 99). Fibroblast growth factor 23 (FGF23), a newly described phosphaturic hormone, inhibits renal production of Calcitriol [1,25-dihydroxyvitamin D or 1,25(OH)2D] by inhibiting 1-α-hydroxylase in the renal proximal tubule and by simultaneously increasing the expression of 24-α-hydroxylase and production of 24,25(OH)2D (an inactive metabolite) 100). Calcitriol [1,25-dihydroxyvitamin D or 1,25(OH)2D] stimulates fibroblast growth factor 23 (FGF23), creating a feedback loop. Fibroblast growth factor 23 (FGF23) decreases renal reabsorption of phosphate, and thereby counteracts the increased gastrointestinal phosphate reabsorption induced by Calcitriol, maintaining phosphate homeostasis 101).
When hypocalcemia (low blood calcium) occurs, serum parathyroid hormone (PTH) concentration increases and enhances renal tubular reabsorption of calcium, as well as the activity of 1-α-hydroxylase in the kidney. This results in increased Calcitriol [1,25-dihydroxyvitamin D or 1,25(OH)2D] production, and in turn, intestinal calcium absorption. Parathyroid hormone (PTH) also stimulates bone osteoclast activity to mobilize bone calcium stores, thereby increasing serum calcium. Both Calcitriol and Calcidiol [25-hydroxyvitamin D or 25(OH)D] are degraded in part by being hydroxylated at the 24 position by a 24-hydroxylase. The activity of the 24-hydroxylase gene is increased by calcitriol (which therefore promotes its own inactivation) and reduced by parathyroid hormone (thereby allowing more active hormone to be formed) 102). Estrogen, placental growth hormone, and prolactin may also regulate vitamin D metabolism, playing a role during pregnancy to meet increased calcium demands. Calcitriol is also formed in some other tissues, but is used only within the tissues and not circulated. Parathyroid hormone (PTH)- independent extrarenal production of Calcitriol from Calcidiol is by activated macrophages in the lung and lymph nodes. The 1-α-hydroxylase enzyme is also expressed at other extrarenal sites, including the gastrointestinal tract, skin, vasculature, mammary epithelial cells, and in osteoblasts and osteoclasts 103).
Vitamin D is a nutrient found in some foods that is needed for health and to maintain strong bones. It does so by helping the body absorb calcium (one of bone’s main building blocks) from food and supplements. People who get too little vitamin D may develop soft, thin, and brittle bones, a condition known as rickets in children and osteomalacia in adults.
Vitamin D is important to the body in many other ways as well. Muscles need it to move, for example, nerves need it to carry messages between the brain and every body part, and the immune system needs vitamin D to fight off invading bacteria and viruses. Together with calcium, vitamin D also helps protect older adults from osteoporosis. Vitamin D is found in cells throughout the body.
Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and to prevent hypocalcemic tetany. It is also needed for bone growth and bone remodeling by osteoblasts and osteoclasts 104), 105). Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Vitamin D sufficiency prevents rickets in children and osteomalacia in adults 106). Together with calcium, vitamin D also helps protect older adults from osteoporosis.
Vitamin D has other roles in the body, including modulation of cell growth, neuromuscular and immune function, and reduction of inflammation 107), 108), 109). Many genes encoding proteins that regulate cell proliferation, differentiation, and apoptosis are modulated in part by vitamin D 110). Many cells have vitamin D receptors, and some convert 25-hydroxyvitamin D (25(OH)D or calcidiol) to calcitriol [1,25-dihydroxyvitamin D or 1,25(OH)2D].
Serum concentration of 25-hydroxyvitamin D (25(OH)D or calcidiol) is the best indicator of vitamin D status. It reflects vitamin D produced cutaneously and that obtained from food and supplements 111) and has a fairly long circulating half-life of 15 days 112). 25-hydroxyvitamin D (25(OH)D or calcidiol) functions as a biomarker of exposure, but it is not clear to what extent 25-hydroxyvitamin D (25(OH)D or calcidiol) levels also serve as a biomarker of effect (i.e., relating to health status or outcomes) 113). Serum 25-hydroxyvitamin D (25(OH)D or calcidiol) levels do not indicate the amount of vitamin D stored in body tissues.
In contrast to 25-hydroxyvitamin D [25(OH)D or calcidiol], circulating Calcitriol [1,25-dihydroxyvitamin D or 1,25(OH)2D] is generally not a good indicator of vitamin D status because it has a short half-life of 15 hours and serum concentrations are closely regulated by parathyroid hormone, calcium, and phosphate 114). Levels of 1,25(OH)2D do not typically decrease until vitamin D deficiency is severe 115), 116).
Researchers have not definitively identified serum concentrations of 25-hydroxyvitamin D [25(OH)D] associated with deficiency (e.g., rickets), adequacy for bone health, and overall health. After reviewing data on vitamin D needs, an expert committee of the Food and Nutrition Board at the National Academies of Sciences, Engineering, and Medicine concluded that people are at risk of vitamin D deficiency at serum 25-hydroxyvitamin D [25(OH)D] concentrations less than 30 nmol/L (12 ng/mL; see Table 5 for definitions of “deficiency” and “inadequacy”) 117). Some people are potentially at risk of inadequacy at 30 to 50 nmol/L (12–20 ng/mL). Levels of 50 nmol/L (20 ng/mL) or more are sufficient for most people. In contrast, the Endocrine Society stated that, for clinical practice, a serum 25(OH)D concentration of more than 75 nmol/L (30 ng/mL) is necessary to maximize the effect of vitamin D on calcium, bone, and muscle metabolism 118). The Food and Nutrition Board committee also noted that serum concentrations greater than 125 nmol/L (50 ng/mL) can be associated with adverse effects (Table 5).
Optimal serum concentrations of 25-hydroxyvitamin D [25(OH)D] for bone and general health have not been established because they are likely to vary by stage of life, by race and ethnicity, and with each physiological measure used 119). In addition, although 25-hydroxyvitamin D [25(OH)D] levels rise in response to increased vitamin D intake, the relationship is nonlinear 120). The amount of increase varies, for example, by baseline serum levels and duration of supplementation.
An additional complication in assessing vitamin D status is in the actual measurement of 25-hydroxyvitamin D (25(OH)D or calcidiol) concentrations. Considerable variability exists among the various assays available (the two most common methods being antibody based and liquid chromatography based) and among laboratories that conduct the analyses 121), 122), 123). This means that compared with the actual concentration of 25-hydroxyvitamin D (25(OH)D or calcidiol) in a sample of blood serum, a falsely low or falsely high value may be obtained depending on the assay or laboratory used 124). A standard reference material for 25-hydroxyvitamin D (25(OH)D or calcidiol) became available in July 2009 that permits standardization of values across laboratories and may improve method-related variability 125), 126).
Table 5. Serum 25-Hydroxyvitamin D [25(OH)D] Concentrations and Health
|<30||<12||Associated with vitamin D deficiency, leading to rickets|
in infants and children and osteomalacia in adults
|30 to <50||12 to <20||Generally considered inadequate for bone and overall health|
in healthy individuals
|≥50||≥20||Generally considered adequate for bone and overall health|
in healthy individuals
|>125||>50||Emerging evidence links potential adverse effects to such|
high levels, particularly >150 nmol/L (>60 ng/mL)
* Serum concentrations of 25(OH)D are reported in both nanomoles per liter (nmol/L) and nanograms per milliliter (ng/mL).
** 1 nmol/L = 0.4 ng/mL and 1 ng/mL = 2.5 nmol/L.
What is a low vitamin D level?
There is a bit of controversy regarding what is considered a low vitamin D level between different expert organizations. A vitamin D level measures levels of 25-hydroxyvitamin D [25(OH)D] also known as calcidiol, in the blood.
Most experts recommend:
- Levels of 20-50 nanograms/milliliter (ng/ml) of 25(OH)D: Sufficient (good)
- Levels of 12-19 ng/ml: Borderline
- Levels of less than 12 ng/ml: Deficient (low)
However, not everybody agrees, and some organizations suggest different cut-off values.
The Institute of Medicine states:
- Levels above 20 ng/ml: Sufficient
- Levels below 20 ng/ml: Deficient
Note that several members of the Institute of Medicine committee publicly stated that over screening for vitamin D deficiency was a problem which typically resulted in unnecessary treatment. They were not in agreement with a cut-off level of 20 ng/ml for deficiency and recommended a lower level of 12.5 ng/ml.
The Endocrine Society states:
- Levels above 30 ng/ml: Sufficient; however, some assays are inaccurate and levels of 40-60 ng/ml better guarantee sufficiency
- Levels of 21-29 ng/ml: Insufficient
- Levels below 20 ng/ml: Deficient
Talk to your doctor about what he/she considers to be a low vitamin D level.
How much vitamin D do you need?
Intake reference values for vitamin D and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of The National Academies 128). DRI is the general term for a set of reference values used to plan and assess nutrient intakes of healthy people. These values, which vary by age and gender, include:
- Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy people.
- Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
- Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects 129).
The Food and Nutrition Board (FNB) established an RDA for vitamin D representing a daily intake that is sufficient to maintain bone health and normal calcium metabolism in healthy people. RDAs for vitamin D are listed in both International Units (IUs) and micrograms (mcg); the biological activity of 40 IU is equal to 1 mcg (Table 2). Even though sunlight may be a major source of vitamin D for some, the vitamin D RDAs are set on the basis of minimal sun exposure 130).
Table 6. The amount of vitamin D you need each day depends on your age. Average daily recommended amounts from the Food and Nutrition Board (a national group of experts) for different ages are listed below in International Units (IU):
|Life Stage||Recommended Amount|
|Birth to 12 months||400 IU (10 mcg)|
|Children 1–13 years||600 IU (15 mcg)|
|Teens 14–18 years||600 IU (15 mcg)|
|Adults 19–70 years||600 IU (15 mcg)|
|Adults 71 years and older||800 IU (20 mcg)|
|Pregnant and breastfeeding women||600 IU (15 mcg)|
Footnote: The amount of vitamin D contained in supplements is sometimes expressed in international units (IU) where 40 IU is equal to one microgram (1 mcg) of vitamin D.[Source 131) ]
Patients with vitamin D deficiency need much higher doses 132). The upper limit of safety for vitamin D is 4000 IU/day. There are currently differing recommendations regarding the optimal 25-hydroxyvitamin D (25-OHD) level for bone health with the Institute of Medicine committee recommending a 25-hydroxyvitamin D (25-OHD) level ≥20-29 ng/mL while several other societies recommend a 25-OHD level ≥30 ng/mL 133).
In the presence of vitamin D deficiency, it is safe to normalize vitamin D levels to a 25-hydroxyvitamin D (25-OHD) level of 30 ng/ml to prevent the compensatory rise in parathyroid hormone (PTH) level 134) . This may be done in a variety of ways. One approach is shown in Table 7 below. High doses of vitamin D are needed [e.g., 50,000 IU of vitamin D2 (ergocalciferol) weekly for 8 weeks or according to the 25-hydroxyvitamin D level] 135). Individuals with malabsorption often require very high doses of supplemental vitamin D.
Table 7. Vitamin D repletion to achieve a 25-hydroxy (25-OH) vitamin D level of 30 to 32 ng/ml
|25-(OH) Vitamin D||Recommended Treatment Dose|
|< 10 ng/ml||Evaluation by a bone specialist.|
|< 20 ng/ml||50,000 IU Vitamin D2 weekly for 8 weeks and then recheck level. Once sufficient level is reached, consider maintenance with 800-1000 IU of Vitamin D3 daily or 50,000 IU Vitamin D2 once or twice monthly as needed.|
|≤ 25 ng/ml||50,000 IU of Vitamin D2 every 2 weeks for 4 weeks and then consider maintenance with 800-1000 IU of Vitamin D3 daily or 50,000 IU Vitamin D2 once or twice monthly as needed. (opinion based)|
What foods provide vitamin D?
Very few foods naturally have vitamin D. The flesh of fatty fish (such as salmon, tuna, and mackerel) and fish liver oils are among the best sources 137), 138). Small amounts of vitamin D are found in beef liver, cheese, and egg yolks. Vitamin D in these foods is primarily in the form of vitamin D3 and its metabolite 25(OH)D3 139). Some mushrooms provide vitamin D2 in variable amounts 140), 141). Mushrooms with enhanced levels of vitamin D2 from being exposed to ultraviolet light under controlled conditions are also available.
The U.S. Department of Agriculture’s (USDA’s) FoodData Central (https://fdc.nal.usda.gov) lists the nutrient content of many foods and provides a comprehensive list of foods containing vitamin D arranged by nutrient content (https://ods.od.nih.gov/pubs/usdandb/VitaminD-Content.pdf) and by food name (https://ods.od.nih.gov/pubs/usdandb/VitaminD-Food.pdf). However, FoodData Central does not include the amounts of 25(OH)D in foods. A variety of foods and their vitamin D levels per serving are listed in Table 8.
Fortified foods provide most of the vitamin D in the American diet 142), 143). For example, almost all of the U.S. milk supply is voluntarily fortified with 100 IU/cup 144). (In Canada, milk is fortified by law with 35–40 IU/100 mL, as is margarine at ≥530 IU/100 g.) In the 1930s, a milk fortification program was implemented in the United States to combat rickets, then a major public health problem 145). Other dairy products made from milk, such as cheese and ice cream, are generally not fortified. Ready-to-eat breakfast cereals often contain added vitamin D, as do some brands of orange juice, yogurt, margarine and other food products.
Both the United States and Canada mandate the fortification of infant formula with vitamin D: 40–100 IU/100 kcal in the United States and 40–80 IU/100 kcal in Canada 146).
Fortified foods provide most of the vitamin D in American diets:
- Fatty fish such as salmon, tuna, and mackerel are among the best sources.
- Beef liver, cheese, and egg yolks provide small amounts.
- Mushrooms provide some vitamin D. In some mushrooms that are newly available in stores, the vitamin D content is being boosted by exposing these mushrooms to ultraviolet light.
- Almost all of the U.S. milk supply is fortified with 400 IU of vitamin D per quart. But foods made from milk, like cheese and ice cream, are usually not fortified.
- Vitamin D is added to many breakfast cereals and to some brands of orange juice, yogurt, margarine, and soy beverages; check the labels.
Animal-based foods typically provide some vitamin D in the form of 25(OH)D in addition to vitamin D3. The impact of this form on vitamin D status is an emerging area of research. Studies show that 25(OH)D appears to be approximately five times more potent than the parent vitamin for raising serum 25(OH)D concentrations 147). One study found that when the 25(OH)D content of beef, pork, chicken, turkey, and eggs is taken into account, the total amount of vitamin D in the food is 2 to 18 times higher than the amount in the parent vitamin alone, depending on the food 148). At the present time, the U.S. Department of Agriculture, Agricultural Research Service (USDA’s) Nutrient Database does not include 25(OH)D when reporting the vitamin D content of foods. Actual vitamin D intakes in the U.S. population may be underestimated for this reason.
Table 8. Vitamin D content of selected foods
|Cod liver oil, 1 tablespoon||34||1360||170|
|Trout (rainbow), farmed, cooked, 3 ounces||16.2||645||81|
|Salmon (sockeye), cooked, 3 ounces||14.2||570||71|
|Mushrooms, white, raw, sliced, exposed to UV light, ½ cup||9.2||366||46|
|Milk, 2% milkfat, vitamin D fortified, 1 cup||2.9||120||15|
|Soy, almond, and oat milks, vitamin D fortified, various brands, 1 cup||2.5-3.6||100-144||13-18|
|Ready-to-eat cereal, fortified with 10% of the DV for vitamin D, 1 serving||2||80||10|
|Sardines (Atlantic), canned in oil, drained, 2 sardines||1.2||46||6|
|Egg, 1 large, scrambled**||1.1||44||6|
|Liver, beef, braised, 3 ounces||1||42||5|
|Tuna fish (light), canned in water, drained, 3 ounces||1||40||5|
|Cheese, cheddar, 1 ounce||0.3||12||2|
|Mushrooms, portabella, raw, diced, ½ cup||0.1||4||1|
|Chicken breast, roasted, 3 ounces||0.1||4||1|
|Beef, ground, 90% lean, broiled, 3 ounces||0||1.7||0|
|Broccoli, raw, chopped, ½ cup||0||0||0|
|Carrots, raw, chopped, ½ cup||0||0||0|
|Almonds, dry roasted, 1 ounce||0||0||0|
|Rice, brown, long-grain, cooked, 1 cup||0||0||0|
|Whole wheat bread, 1 slice||0||0||0|
|Lentils, boiled, ½ cup||0||0||0|
|Sunflower seeds, roasted, ½ cup||0||0||0|
|Edamame, shelled, cooked, ½ cup||0||0||0|
Footnotes: The amount of vitamin D contained in supplements is sometimes expressed in international units (IU) where 40 IU is equal to one microgram (1 mcg) of vitamin D.
* DV = Daily Value. The FDA developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for vitamin D is 20 mcg (800 IU) for adults and children aged 4 years and older. The labels must list vitamin D content in mcg per serving and have the option of also listing the amount in IUs in parentheses. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.
** Vitamin D is in the yolk.[Source 149) ]
What kinds of vitamin D dietary supplements are available?
Vitamin D is found in supplements (and fortified foods) in two different forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Both increase vitamin D in the blood.
In supplements and fortified foods, vitamin D is available in two forms, D2 (ergocalciferol) and D3 (cholecalciferol) that differ chemically only in their side-chain structure. Vitamin D2 is manufactured by the UV irradiation of ergosterol in yeast, and vitamin D3 is manufactured by the irradiation of 7-dehydrocholesterol from lanolin and the chemical conversion of cholesterol 150). The two forms have traditionally been regarded as equivalent based on their ability to cure rickets and, indeed, most steps involved in the metabolism and actions of vitamin D2 and vitamin D3 are identical. Both forms (as well as vitamin D in foods and from cutaneous synthesis) effectively raise serum Calcidiol [25-hydroxyvitamin D or 25(OH)D] levels 151). Firm conclusions about any different effects of these two forms of vitamin D cannot be drawn. However, it appears that at nutritional doses vitamins D2 and D3 are equivalent, but at high doses vitamin D2 is less potent. Some studies suggest that cholecalciferol (Vitamin D3) increases serum Calcidiol [25(OH) D] more efficiently than does ergocalciferol (Vitamin D2) 152).
- Vitamin D3 (cholecalciferol) is available in 400, 800, 1000, 2000, 5000, 10,000, and 60,000 IU capsules. It is available in some countries as an intramuscular injection (Arachital 600,000 IU, which maintains vitamin D levels for 1 year). However, it can be extremely painful 153).
- Vitamin D2 (ergocalciferol) is available for oral use in 400 and 50,000 unit capsules or in a liquid form (8000 IU/mL) 154).
The American Academy of Pediatrics (AAP) recommends that exclusively and partially breastfed infants receive supplements of 400 IU/day of vitamin D shortly after birth and continue to receive these supplements until they are weaned and consume ≥1,000 mL/day of vitamin D-fortified formula or whole milk 155). Similarly, all non-breastfed infants ingesting <1,000 mL/day of vitamin D-fortified formula or milk should receive a vitamin D supplement of 400 IU/day 156). The American Academy of Pediatrics also recommends that older children and adolescents who do not obtain 400 IU/day through vitamin D-fortified milk and foods should take a 400 IU vitamin D supplement daily. However, this latter recommendation (issued November 2008) needs to be reevaluated in light of the Food and Nutrition Board’s vitamin D RDA of 600 IU/day for children and adolescents (issued November 2010 and which previously was an AI of 200 IU/day).
Am I getting enough vitamin D?
Because you get vitamin D from food, sunshine, and dietary supplements, one way to know if you’re getting enough is a blood test that measures the amount of vitamin D in your blood. In the blood, a form of vitamin D known as 25-hydroxyvitamin D is measured in either nanomoles per liter (nmol/L) or nanograms per milliliter (ng/mL). One nmol/L is the same as 0.4 ng/mL.
- Levels of 50 nmol/L (20 ng/mL) or above are adequate for most people for bone and overall health.
- Levels below 30 nmol/L (12 ng/mL) are too low and might weaken your bones and affect your health.
- Levels above 125 nmol/L (50 ng/mL) are too high and might cause health problems.
In the United States, most people have adequate blood levels of vitamin D. However, almost one out of four people have vitamin D blood levels that are too low or inadequate for bone and overall health.
Some people are more likely than others to have trouble getting enough vitamin D:
- Breastfed infants. Breast milk alone does not provide infants with an adequate amount of vitamin D. Breastfed infants should be given a supplement of 10 mcg (400 IU) of vitamin D each day.
- Older adults. As you age, your skin’s ability to make vitamin D when exposed to sunlight declines.
- People who seldom expose their skin to sunshine because they do not go outside or because they keep their body and head covered. Sunscreen also limits the amount of vitamin D your skin produces.
- People with dark skin. The darker your skin, the less vitamin D you make from sunlight exposure.
- People with conditions that limit fat absorption, such as Crohn’s disease, celiac disease, or ulcerative colitis. This is because the vitamin D you consume is absorbed in the gut along with fat, so if your body has trouble absorbing fat, it will also have trouble absorbing vitamin D.
- People who are obese or have undergone gastric bypass surgery. They may need more vitamin D than other people.
Can you get vitamin D from the sun?
Most people meet at least some of their vitamin D needs through exposure to sunlight 157), 158). Ultraviolet (UV) B radiation with a wavelength of 290–320 nanometers penetrates uncovered skin and converts cutaneous 7-dehydrocholesterol to previtamin D3, which in turn becomes vitamin D3 159). Season, time of day, length of day, cloud cover, smog, skin melanin content, and sunscreen are among the factors that affect UV radiation exposure and vitamin D synthesis 160). Perhaps surprisingly, geographic latitude does not consistently predict average serum 25(OH)D levels in a population. Ample opportunities exist to form vitamin D (and store it in the liver and fat) from exposure to sunlight during the spring, summer, and fall months even in the far north latitudes 161).
Complete cloud cover reduces UV energy by 50%; shade (including that produced by severe pollution) reduces it by 60% 162). UVB radiation does not penetrate glass, so exposure to sunshine indoors through a window does not produce vitamin D 163). Sunscreens with a sun protection factor (SPF) of 8 or more appear to block vitamin D-producing UV rays, although in practice people generally do not apply sufficient amounts, cover all sun-exposed skin, or reapply sunscreen regularly 164), 165). Therefore, skin likely synthesizes some vitamin D even when it is protected by sunscreen as typically applied.
The factors that affect UV radiation exposure and research to date on the amount of sun exposure needed to maintain adequate vitamin D levels make it difficult to provide general guidelines. It has been suggested by some vitamin D researchers, for example, that approximately 5–30 minutes of sun exposure between 10 AM and 3 PM at least twice a week to the face, arms, legs, or back without sunscreen usually lead to sufficient vitamin D synthesis and that the moderate use of commercial tanning beds that emit 2%–6% UVB radiation is also effective 166), 167). Individuals with limited sun exposure need to include good sources of vitamin D in their diet or take a supplement to achieve recommended levels of intake.
Despite the importance of the sun for vitamin D synthesis, it is prudent to limit exposure of skin to sunlight 168) and UV radiation from tanning beds 169). UV radiation is a carcinogen responsible for most of the estimated 1.5 million skin cancers and the 8,000 deaths due to metastatic melanoma that occur annually in the United States 170). Lifetime cumulative UV damage to skin is also largely responsible for some age-associated dryness and other cosmetic changes. The American Academy of Dermatology advises that photoprotective measures be taken, including the use of sunscreen, whenever one is exposed to the sun 171). Assessment of vitamin D requirements cannot address the level of sun exposure because of these public health concerns about skin cancer, and there are no studies to determine whether UVB-induced synthesis of vitamin D can occur without increased risk of skin cancer 172).
The body makes vitamin D when skin is directly exposed to the sun, and most people meet at least some of their vitamin D needs this way. Skin exposed to sunshine indoors through a window will not produce vitamin D. Cloudy days, shade, and having dark-colored skin also cut down on the amount of vitamin D the skin makes.
However, despite the importance of the sun to vitamin D synthesis, it is prudent to limit exposure of skin to sunlight in order to lower the risk for skin cancer. When out in the sun for more than a few minutes, wear protective clothing and apply sunscreen with an SPF (sun protection factor) of 15 or more. Tanning beds also cause the skin to make vitamin D, but pose similar risks for skin cancer.
People who avoid the sun or who cover their bodies with sunscreen or clothing should include good sources of vitamin D in their diets or take a supplement. Recommended intakes of vitamin D are set on the assumption of little sun exposure.
How long should you spend in the sun?
Most people can make enough vitamin D from being out in the sun daily for short periods with their forearms, hands or lower legs uncovered and without sunscreen from late March or early April to the end of September, especially from 11am to 3pm.
It’s not known exactly how much time is needed in the sun to make enough vitamin D to meet your body’s requirements. This is because there are a number of factors that can affect how vitamin D is made, such as your skin color or how much skin you have exposed. But you should be careful not to burn in the sun, so take care to cover up, or protect your skin with sunscreen, before your skin starts to turn red or burn.
Your risk of sunburn depends on 2 things. How sun-sensitive your skin is, and how strong the UV rays are you’re exposed to. Different people will have a different risk of sunburn on the same day, so it’s a good idea to know when your risk is high, so you can protect your skin.
In general people who have one or more of the following are at more risk:
- skin that burns easily
- light or fair colored skin, hair, or eyes
- lots of moles or freckles
- a history of sunburn
- a personal or family history of skin cancer
People with dark skin, such as those of African, African-Caribbean or south Asian origin, will need to spend longer in the sun to produce the same amount of vitamin D as someone with lighter skin.
- Children aged under six months should be kept out of direct strong sunlight. To ensure they get enough vitamin D, babies and children aged under five years should be given vitamin D supplements even if they do get out in the sun.
How long it takes for your skin to go red or burn varies from person to person. You’re the best person to know how your skin reacts in the sun. The more easily you get sunburnt, the more careful you need to be. Remember, you don’t need to peel – if your skin’s gone red or pink in the sun, that’s sunburn, and it’s dangerous. For people with darker skin it may feel irritated, tender or itchy. The longer you stay in the sun, especially for prolonged periods without sun protection, the greater your risk of skin cancer. Using sunbeds is not a recommended way of making vitamin D.
Other things that affect the strength of UV rays are the:
- Time of year – the highest risk months in the US are April to September. Near the equator, there are strong UV rays all year round.
- Altitude – UV rays are stronger the higher you go. So skiers and mountaineers can easily get caught out.
- Cloud cover – over 90% of UV can pass through light cloud.
- Reflection – up to 80% of UV rays are reflected back from snow, 15% from sand, 10% from concrete and up to 30% from water (depending on how choppy it is).
Is magnesium good for your bones?
Magnesium is an abundant mineral in your body, is naturally present in many foods, added to other food products, available as a dietary supplement, and present in some medicines (such as antacids and laxatives) 173). Approximately 30% to 40% of the dietary magnesium consumed is typically absorbed by the body 174). Magnesium is a cofactor in more than 300 enzyme systems that regulate diverse biochemical reactions in your body, including protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation 175). Magnesium is required for energy production, oxidative phosphorylation, and glycolysis. Magnesium is involved in bone formation and influences the activities of osteoblasts and osteoclasts 176). Magnesium also affects the concentrations of both parathyroid hormone (PTH) and the active form of vitamin D, which are major regulators of bone homeostasis. Several population-based studies have found positive associations between magnesium intake and bone mineral density in both men and women 177). Other research has found that women with osteoporosis have lower serum magnesium levels than women with osteopenia and those who do not have osteoporosis or osteopenia 178). These and other findings indicate that magnesium deficiency might be a risk factor for osteoporosis 179).
Magnesium is also required for the synthesis of DNA, RNA, and the antioxidant glutathione. Magnesium also plays a role in the active transport of calcium and potassium ions across cell membranes, a process that is important to nerve impulse conduction, muscle contraction, and normal heart rhythm 180).
Although limited in number, studies suggest that increasing magnesium intakes from food or supplements might increase bone mineral density in postmenopausal and elderly women 181). For example, one short-term study found that 290 mg/day elemental magnesium (as magnesium citrate) for 30 days in 20 postmenopausal women with osteoporosis suppressed bone turnover compared with placebo, suggesting that bone loss decreased 182).
Diets that provide recommended levels of magnesium enhance bone health, but further research is needed to elucidate the role of magnesium in the prevention and management of osteoporosis.
An adult body contains approximately 25 g magnesium, with 50% to 60% present in the bones and most of the rest in soft tissues 183). Less than 1% of total magnesium is in blood serum, and these levels are kept under tight control. Normal serum magnesium concentrations range between 0.75 and 0.95 millimoles (mmol)/L 184). Hypomagnesemia is defined as a serum magnesium level less than 0.75 mmol/L 185). Magnesium homeostasis is largely controlled by the kidney, which typically excretes about 120 mg magnesium into the urine each day 186). Urinary excretion is reduced when magnesium status is low 187).
Assessing magnesium status is difficult because most magnesium is inside cells or in bone 188). The most commonly used and readily available method for assessing magnesium status is measurement of serum magnesium concentration, even though serum levels have little correlation with total body magnesium levels or concentrations in specific tissues 189). Other methods for assessing magnesium status include measuring magnesium concentrations in red blood cells, saliva, and urine; measuring ionized magnesium concentrations in blood, plasma, or serum; and conducting a magnesium-loading (or “tolerance”) test. No single method is considered satisfactory 190). Some experts 191) but not others 192) consider the tolerance test (in which urinary magnesium is measured after parenteral infusion of a dose of magnesium) to be the best method to assess magnesium status in adults. To comprehensively evaluate magnesium status, both laboratory tests and a clinical assessment might be required 193).
How much magnesium do I need?
The amount of magnesium you need depends on your age and sex. Average daily recommended amounts are listed below in milligrams (mg). Table 9 lists the current Recommended Dietary Allowances (RDAs) for magnesium 194). For infants from birth to 12 months, the Food and Nutrition Board at the Institute of Medicine of the National Academies established an Adequate Intake (AI) for magnesium that is equivalent to the mean intake of magnesium in healthy, breastfed infants, with added solid foods for ages 7–12 months.
- Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy people.
- Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
- Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects 195).
Table 9. Recommended Dietary Allowances (RDAs) for Magnesium
|Birth to 6 months||30 mg*||30 mg*|
|7–12 months||75 mg*||75 mg*|
|1–3 years||80 mg||80 mg|
|4–8 years||130 mg||130 mg|
|9–13 years||240 mg||240 mg|
|14–18 years||410 mg||360 mg||400 mg||360 mg|
|19–30 years||400 mg||310 mg||350 mg||310 mg|
|31–50 years||420 mg||320 mg||360 mg||320 mg|
|51+ years||420 mg||320 mg|
Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.
Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an Recommended Dietary Allowance (RDA).[Source 196) ]
What foods provide magnesium?
Magnesium is found naturally in many foods and is added to some fortified foods. Green leafy vegetables, such as spinach, legumes, nuts, seeds, and whole grains, are good sources 197). You can get recommended amounts of magnesium by eating a variety of foods, including the following:
- Legumes, nuts, seeds, whole grains, and green leafy vegetables (such as spinach)
- Fortified breakfast cereals and other fortified foods
- Milk, yogurt, and some other milk products
In general, foods containing dietary fiber provide magnesium. Magnesium is also added to some breakfast cereals and other fortified foods. Some types of food processing, such as refining grains in ways that remove the nutrient-rich germ and bran, lower magnesium content substantially 198). Selected food sources of magnesium are listed in Table 10.
Tap, mineral, and bottled waters can also be sources of magnesium, but the amount of magnesium in water varies by source and brand (ranging from 1 mg/L to more than 120 mg/L) 199).
The U.S. Department of Agriculture’s (USDA’s) FoodData Central (https://fdc.nal.usda.gov) lists the nutrient content of many foods and provides comprehensive list of foods containing magnesium arranged by nutrient content (https://ods.od.nih.gov/pubs/usdandb/Magnesium-Content.pdf) and by food name (https://ods.od.nih.gov/pubs/usdandb/Magnesium-Food.pdf).
Table 10. Magnesium content of selected foods
|Pumpkin seeds, roasted, 1 ounce||156||37|
|Chia seeds, 1 ounce||111||26|
|Almonds, dry roasted, 1 ounce||80||19|
|Spinach, boiled, ½ cup||78||19|
|Cashews, dry roasted, 1 ounce||74||18|
|Peanuts, oil roasted, ¼ cup||63||15|
|Cereal, shredded wheat, 2 large biscuits||61||15|
|Soymilk, plain or vanilla, 1 cup||61||15|
|Black beans, cooked, ½ cup||60||14|
|Edamame, shelled, cooked, ½ cup||50||12|
|Peanut butter, smooth, 2 tablespoons||49||12|
|Potato, baked with skin, 3.5 ounces||43||10|
|Rice, brown, cooked, ½ cup||42||10|
|Yogurt, plain, low fat, 8 ounces||42||10|
|Breakfast cereals, fortified with 10% of the DV for magnesium, 1 serving||42||10|
|Oatmeal, instant, 1 packet||36||9|
|Kidney beans, canned, ½ cup||35||8|
|Banana, 1 medium||32||8|
|Salmon, Atlantic, farmed, cooked, 3 ounces||26||6|
|Milk, 1 cup||24–27||6|
|Halibut, cooked, 3 ounces||24||6|
|Raisins, ½ cup||23||5|
|Bread, whole wheat, 1 slice||23||5|
|Avocado, cubed, ½ cup||22||5|
|Chicken breast, roasted, 3 ounces||22||5|
|Beef, ground, 90% lean, pan broiled, 3 ounces||20||5|
|Broccoli, chopped and cooked, ½ cup||12||3|
|Rice, white, cooked, ½ cup||10||2|
|Apple, 1 medium||9||2|
|Carrot, raw, 1 medium||7||2|
Footnote: *DV = Daily Value. The U.S. Food and Drug Administration (FDA) developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. The DV for magnesium is 420 mg for adults and children aged 4 years and older. FDA does not require food labels to list magnesium content unless magnesium has been added to the food. Foods providing 20% or more of the DV are considered to be high sources of a nutrient, but foods providing lower percentages of the DV also contribute to a healthful diet.[Source 200) ]
Magnesium supplements are available in a variety of forms, including magnesium oxide, citrate, and chloride 201). The Supplement Facts panel on a dietary supplement label declares the amount of elemental magnesium in the product, not the weight of the entire magnesium-containing compound.
Absorption of magnesium from different kinds of magnesium supplements varies. Forms of magnesium that dissolve well in liquid are more completely absorbed in the gut than less soluble forms 202). Small studies have found that magnesium in the aspartate, citrate, lactate, and chloride forms is absorbed more completely and is more bioavailable than magnesium oxide and magnesium sulfate 203). One study found that very high doses of zinc from supplements (142 mg/day) can interfere with magnesium absorption and disrupt the magnesium balance in the body 204).
Several types of medications have the potential to interact with magnesium supplements or affect magnesium status. A few examples are provided below. People taking these and other medications on a regular basis should discuss their magnesium intakes with their healthcare providers.
- Bisphosphonates: Magnesium-rich supplements or medications can decrease the absorption of oral bisphosphonates, such as alendronate (Fosamax®), used to treat osteoporosis 205). Use of magnesium-rich supplements or medications and oral bisphosphonates should be separated by at least 2 hours.
- Antibiotics: Magnesium can form insoluble complexes with tetracyclines, such as demeclocycline (Declomycin®) and doxycycline (Vibramycin®), as well as quinolone antibiotics, such as ciprofloxacin (Cipro®) and levofloxacin (Levaquin®). These antibiotics should be taken at least 2 hours before or 4–6 hours after a magnesium-containing supplement 206).
- Diuretics: Chronic treatment with loop diuretics, such as furosemide (Lasix®) and bumetanide (Bumex®), and thiazide diuretics, such as hydrochlorothiazide (Aquazide H®) and ethacrynic acid (Edecrin®), can increase the loss of magnesium in urine and lead to magnesium depletion 207). In contrast, potassium-sparing diuretics, such as amiloride (Midamor®) and spironolactone (Aldactone®), reduce magnesium excretion 208).
- Proton pump inhibitors: Prescription proton pump inhibitor (PPI) drugs, such as esomeprazole magnesium (Nexium®) and lansoprazole (Prevacid®), when taken for prolonged periods (typically more than a year) can cause hypomagnesemia 209). In cases that FDA reviewed, magnesium supplements often raised the low serum magnesium levels caused by PPIs. However, in 25% of the cases, supplements did not raise magnesium levels and the patients had to discontinue the PPI. FDA advises healthcare professionals to consider measuring patients’ serum magnesium levels prior to initiating long-term PPI treatment and to check magnesium levels in these patients periodically 210).
Health risks from excessive magnesium
Too much magnesium from food does not pose a health risk in healthy individuals because the kidneys eliminate excess amounts in the urine 211). However, high doses of magnesium from dietary supplements or medications often result in diarrhea that can be accompanied by nausea and abdominal cramping 212). Forms of magnesium most commonly reported to cause diarrhea include magnesium carbonate, chloride, gluconate, and oxide 213). The diarrhea and laxative effects of magnesium salts are due to the osmotic activity of unabsorbed salts in the intestine and colon and the stimulation of gastric motility.
Very large doses of magnesium-containing laxatives and antacids (typically providing more than 5,000 mg/day magnesium) have been associated with magnesium toxicity 214), including fatal hypermagnesemia in a 28-month-old boy 215) and an elderly man 216). Symptoms of magnesium toxicity, which usually develop after serum concentrations exceed 1.74–2.61 mmol/L, can include hypotension, nausea, vomiting, facial flushing, retention of urine, ileus, depression, and lethargy before progressing to muscle weakness, difficulty breathing, extreme hypotension, irregular heartbeat, and cardiac arrest 217). The risk of magnesium toxicity increases with impaired renal function or kidney failure because the ability to remove excess magnesium is reduced or lost 218).
The Food and Nutrition Board at the Institute of Medicine of the National Academies has established Tolerable Upper Intake Levels (ULs) for magnesium that apply only to supplemental magnesium for healthy infants, children, and adults (see Table 11) 219).
Table 11. Tolerable Upper Intake Levels (ULs) for Supplemental Magnesium
|Birth to 12 months||None established||None established|
|1–3 years||65 mg||65 mg|
|4–8 years||110 mg||110 mg|
|9–18 years||350 mg||350 mg||350 mg||350 mg|
|19+ years||350 mg||350 mg||350 mg||350 mg|
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