- What is Calcium
- Regulation of Calcium Absorption and Metabolism
- Calcium Supplements
- What are some benefits of Calcium on Health
- How much calcium do you need per day ?
- What foods provide calcium?
- Calcium Deficiency
- Calcium as Medicines
- Can too much calcium be harmful ?
What is Calcium
Calcium, the most abundant mineral in the body, is found in some foods, added to others, available as a dietary supplement, and present in some medicines (such as gastric antacids e.g. calcium phosphate 1). Calcium is a mineral that the body needs for numerous functions, including building and maintaining bones and teeth, blood clotting, the transmission of nerve impulses, and the regulation of the heart’s rhythm 2). Ninety-nine percent of the calcium in the human body is stored in the bones and teeth. Calcium is required for vascular contraction and vasodilation, muscle function, nerve transmission, intracellular signaling and hormonal secretion, though less than 1% of total body calcium is needed to support these critical metabolic functions 3). 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 4).
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 5).
The 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 6).
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 7).
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.
Regulation of Calcium Absorption and Metabolism
The metabolism of calcium and of phosphate is intimately related. 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 8).
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 9). Other factors also affect calcium absorption including the following:
- Amount consumed: the efficiency of absorption decreases as calcium intake increases 10).
- 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 11). 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 12).
- Vitamin D intake: this nutrient, obtained from food and produced by skin when exposed to sunlight of sufficient intensity, improves calcium absorption 13).
- 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 14). 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 15). In contrast, wheat products (with the exception of wheat bran) do not appear to lower calcium absorption 16). 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 17). High protein intake also increases calcium excretion and was therefore thought to negatively affect calcium status 18). 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 19).
- Caffeine intake: this stimulant in coffee and tea can modestly increase calcium excretion and reduce absorption 20). One cup of regular brewed coffee, for example, causes a loss of only 2–3 mg of calcium 21). Moderate caffeine consumption (1 cup of coffee or 2 cups of tea per day) in young women has no negative effects on bone 22).
- Alcohol intake: alcohol intake can affect calcium status by reducing its absorption 23) and by inhibiting enzymes in the liver that help convert vitamin D to its active form 24). 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 25).
- Fruit and vegetable intakes: metabolic acids produced by diets high in protein and cereal grains increase calcium excretion 26). 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.
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 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 27). 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 28). Calcium citrate is also useful for people with achlorhydria, inflammatory bowel disease, or absorption disorders 29). 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 30).
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 31). 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 32), 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 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 33), 34), 35), 36). 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 37). Nevertheless, supplementation with vitamin D3 and calcium reduces the risk of hip fractures and other nonvertebral fractures among elderly women 38). 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 39).
Calcium Citrate for Kidney Stone Treatment
Kidney stones are one of the most common disorders of the urinary tract. They typically affect people aged 40 to 60 years of age and are twice as common in men than women although recent data suggest the risks are more equal. Calcium stones are the most common type of kidney stone and occur in two major forms: calcium oxalate and calcium phosphate. Kidney stones can cause severe abdominal pain and may require urgent treatment; they are one of the main causes of unscheduled admissions in urological practice. Following treatment even first time stone formers have a risk for recurrence which increased with each subsequent stone. This increased risk of recurrence of stones is mainly attributed to altered composition of urine i.e. low citrate levels. These people have a higher incidence of calcium phosphate and calcium oxalate stones. Various prevention strategies including increased fluid intake and oral citrate supplements have been tried to modify the chemical composition of the urine. Citrate therapy is believed to stop crystals from growing into stones. Oral citrate therapy increases the urinary citrate levels, which in turn binds with calcium and inhibits the crystallisation thus reduces stone formation. Despite the widespread use of oral citrate therapy for prevention and treatment of calcium oxalate stones, the evidence to support its clinical efficacy remains uncertain.
In a Cochrane review with 477 subjects, most of whom had oxalate stones. Of these, 247 participants compared potassium citrate with placebo or no intervention; 166 participants compared potassium‐sodium citrate with no intervention; and 64 participants compared potassium‐magnesium citrate with placebo. Overall, quality of the reporting of the included studies was considered moderate to poor, and there was a high risk of attrition bias in two studies.
Compared with placebo or no intervention, citrate therapy significantly reduced the stone size (4 studies, 160 participants). New stone formation was significantly lower with citrate therapy compared to control (7 studies, 324 participants). The beneficial effect on stone size stability was also evident (4 studies, 160 participants). Adverse events were reported in four studies, with the main side effects being upper gastrointestinal disturbance and one patient reported a rash. There were more gastrointestinal adverse events in the citrate group; however this was not significant (4 studies, 271 participants). There were significantly more dropouts due to adverse events with citrate therapy compared to control (4 studies, 271 participants). The need for retreatment was significantly less with citrate therapy compared to control (2 studies, 157 participants).
Authors’ conclusions: Citrate salts prevent new stone formation and reduce further stone growth in patients with residual stones that predominantly contain oxalate. The quality of reported literature remains moderate to poor; hence a well‐designed statistically powered multi‐centre random controlled trial is needed in order to answer relevant questions concerning the efficacy of citrate salts 40).
Calcium Acetate as Phosphate binders for preventing and treating bone disease in chronic kidney disease patients
People with chronic kidney disease (CKD) develop impaired excretion of the dietary phosphorus. This results in a condition known as mineral and bone disorder in chronic kidney disease (CKD‐MBD). Mineral and bone disorder in chronic kidney disease is characterized by high bone turnover, increased musculoskeletal morbidity including bone pain and muscle weakness, and vascular calcification which may contribute to the high incidence of cardiovascular disease and associated deaths. Several agents such as phosphate binders, vitamin D compounds, and calcimimetics are widely used to slow the development and progression of mineral and bone disorder in chronic kidney disease complications.
Several phosphate binders, including aluminium and calcium‐containing agents, have been widely used since 1970. The use of newer non‐calcium or aluminium‐based agents, such as sevelamer hydrochloride compounds and lanthanum carbonate is increasing although the cost is greater than the older phosphate binders. The avoidance of calcium‐based binding agents to lower phosphorus in chronic kidney disease theoretically reduces the risk of vascular calcification and cardiovascular disease. The balance between calcium‐free phosphate binders reducing clinical events in chronic kidney disease versus their cost remains controversial. Recently released KDIGO guidelines recommend restricting the use of calcium‐based binders in people with persistent or recurrent hypercalcaemia or arterial calcification, or both.
A review of 60 studies involving 7631 participants comparing phosphate binders to placebo or other phosphate binders. There was no significant reduction in all‐cause mortality (10 studies, 3079 participants) or serum calcium by phosphorus product with sevelamer hydrochloride compared to calcium‐based agents. There was a significant reduction in phosphorus (16 studies, 3126 participants) and parathyroid hormone (12 studies, 2551 participants) levels, but a significant increase in the risk of hypercalcaemia (12 studies, 1144 participants) with calcium salts compared to sevelamer hydrochloride. There was a significant increase in the risk of adverse gastrointestinal events with sevelamer hydrochloride compared to calcium salts (5 studies, 498 participants). Compared with calcium‐based agents, lanthanum significantly reduced serum calcium (2 studies, 122 participants) and the calcium by phosphorous product, but not serum phosphorus levels. The effects of calcium acetate on biochemical end‐points were similar to those of calcium carbonate. The phosphorus lowering effects of novel agents such as ferric citrate, colestilan and niacinamide were only reported in a few studies.
Conclusion of this review is that available phosphate‐binding agents have been shown to reduce phosphorus levels in comparison to placebo. However, there are insufficient data to establish the comparative superiority of novel non‐calcium binding agents over calcium‐containing phosphate binders for patient‐level outcomes such as all‐cause mortality and cardiovascular end‐points in chronic kidney disease 41). This finding is in agreement with another meta-analysis comparing the effects of calcium-based versus non-calcium-based phosphate binders on mortality, cardiovascular events and vascular calcification in patients with chronic kidney disease. Despite the trends observed, the study authors did not find a statistically significant difference in cardiovascular mortality and coronary artery calcification in patients receiving calcium-based phosphate binders compared to non-calcium-based phosphate binders. However, the data are limited by the small number of studies and the confidence intervals do not exclude a potentially important beneficial effect. Therefore, further randomized trials are required 42).
Calcium Supplements Side Effects
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 43). 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 44).
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 45). Although very high calcium intakes have the potential to cause hypercalcemia 46), it is most commonly associated with primary hyperparathyroidism or malignancy 47).
Consuming too much calcium—in excess of 5 grams a day, or 3 grams a day in people with existing kidney problems 48) 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 49). 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 50). Rare harmful side effects from excess calcium include kidney stones 51), hypercalcemia (too much calcium in the blood), and kidney failure 52). 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 53), 54), 55).
What are some benefits of Calcium on Health
Many claims are made about calcium’s potential benefits in health promotion and disease prevention and treatment.
Scientists are studying calcium to understand how it affects health. Here are several examples of what this research has shown:
Bone health and osteoporosis
Bones increase in size and mass during periods of growth in childhood and adolescence, reaching peak bone mass around age 30. The greater the peak bone mass, the longer one can delay serious bone loss with increasing age. Everyone should therefore consume adequate amounts of calcium and vitamin D throughout childhood, adolescence, and early adulthood. Osteoporosis, a disorder characterized by porous and fragile bones, is a serious public health problem for more than 10 million U.S. adults, 80% of whom are women. (Another 34 million have osteopenia, or low bone mass, which precedes osteoporosis.) Osteoporosis is most associated with fractures of the hip, vertebrae, wrist, pelvis, ribs, and other bones 56). An estimated 1.5 million fractures occur each year in the United States due to osteoporosis 57).
When calcium intake is low or ingested calcium is poorly absorbed, bone breakdown occurs as the body uses its stored calcium to maintain normal biological functions. Bone loss also occurs as part of the normal aging process, particularly in postmenopausal women due to decreased amounts of estrogen. Many factors increase the risk of developing osteoporosis, including being female, thin, inactive, or of advanced age; smoking cigarettes; drinking excessive amounts of alcohol; and having a family history of osteoporosis 58).
Various bone mineral density (BMD) tests are available. The T-score from these tests compares an individual’s BMD to an optimal BMD (that of a healthy 30-year old adult). A T-score of -1.0 or above indicates normal bone density, -1.0 to -2.5 indicates low bone mass (osteopenia), and lower than -2.5 indicates osteoporosis 59). Although osteoporosis affects individuals of all races, ethnicities, and both genders, women are at highest risk because their skeletons are smaller than those of men and because of the accelerated bone loss that accompanies menopause. Regular exercise and adequate intakes of calcium and vitamin D are critical to the development and maintenance of healthy bones throughout the life cycle. Both weight-bearing exercises (such as walking, running, and activities where one’s feet leave and hit the ground and work against gravity) and resistance exercises (such as calisthenics and that involve weights) support bone health.
Supplementation with calcium plus vitamin D has been shown to be effective in reducing fractures and falls (which can cause fractures) in institutionalized older adults 60). However, among community-dwelling older adults over age 50, the benefits of supplementation with these nutrients on fracture resistance are much less clear. A recent systematic review of 26 randomized controlled trials found that calcium supplements, with or without vitamin D, modestly but significantly reduced the risk of total and vertebral fractures, but not fractures of the hip or forearm 61). But the four trials with the lowest risk of bias, involving a total of 44,505 individuals, showed no effect of supplementation on risk of fracture at any site. A related meta-analysis of calcium intake on bone mineral density found that calcium supplementation produced only a small, initial, and non-progressive increase in bone mineral density that was unlikely to result in a clinically significant reduction in the risk of bone fractures 62). The U.S. Preventive Services Task Force (USPSTF) concluded that the current evidence is insufficient to assess the balance of benefits and harms of combined vitamin D and calcium supplementation to prevent bone fractures in premenopausal women or in men 63). For non-institutionalized postmenopausal women, the USPSTF concluded that while current evidence was insufficient to assess the balance of benefits and harms of combined supplementation with vitamin D (at more than 400 IU/day) and calcium (at more than 1,000 mg/day) to prevent bone fractures, there was clearly no benefit in supplementing with smaller doses of these nutrients for this purpose.
In 1993, the U.S. Food and Drug Administration authorized a health claim related to calcium and osteoporosis for foods and supplements 64). In January 2010, this health claim was expanded to include vitamin D. Model health claims include the following: “Adequate calcium throughout life, as part of a well-balanced diet, may reduce the risk of osteoporosis” and “Adequate calcium and vitamin D as part of a healthful diet, along with physical activity, may reduce the risk of osteoporosis in later life” 65).
Cancer of the colon and rectum
The results of epidemiologic studies regarding the relationship between calcium intake and colorectal cancer risk have not always been consistent 66).
In the American Cancer Society’s Cancer Prevention Study II Nutrition Cohort, the diet, medical history, and lifestyle of more than 120,000 men and women were analyzed 67). Men and women who had the highest intakes of calcium through both their diet and supplement use had a modestly reduced risk of colorectal cancer compared with those who had the lowest calcium intakes. However, the benefit from calcium appeared to plateau, or level off, at an intake of approximately 1200 mg per day. When calcium from the diet was analyzed by itself, no reduction in colorectal cancer risk was found. However, the use of calcium supplements in any amount was associated with reduced risk. This association was strongest (a 31 percent reduction in risk) for people who took calcium supplements of 500 mg per day or more.
A stronger relationship between calcium intake and colorectal cancer risk was found when participants of the Nurses’ Health Study and the Health Professionals Follow-up Study were combined in an analysis that included more than 135,000 men and women 68). Individuals who had a calcium intake of more than 700 mg per day had a 35 percent to 45 percent reduced risk of cancer of the distal (lower) part of the colon than those who had a calcium intake of 500 mg or less per day. No association was found between calcium intake and risk of cancer of the proximal (middle and upper) part of the colon 69). Another large study of Finnish men showed a similar relationship between higher calcium intake and reduced risk of colorectal cancer 70). This study, however, did not evaluate proximal and distal colorectal cancers separately.
In a study that included more than 61,000 Swedish women, colorectal cancer risk was approximately 28 percent lower among individuals who had the highest calcium intakes (approximately 800–1000 mg per day) compared with those with the lowest calcium intakes (approximately 400–500 mg per day) 71). Data from this study also suggested that the benefit associated with calcium was limited to the distal colon 72). In a study that involved more than 34,000 postmenopausal Iowa women, high intakes of calcium (approximately 1280 mg per day or more) compared with lower calcium intakes (approximately 800 mg per day or less) from both the diet and supplements were associated with a 41 percent reduction in risk of rectal cancer 73). Reduced risks of rectal cancer were also observed for dietary calcium alone and supplemental calcium alone, but these associations were not statistically significant 74).
In an analysis involving more than 293,000 men and 198,000 women in the National Institutes of Health-American Association of Retired Persons (NIH-AARP) Diet and Health Study, high intakes of total calcium, dietary calcium, and supplemental calcium were associated with an approximately 20 percent lower risk of colorectal cancer among men and an approximately 30 percent lower risk of colorectal cancer among women 75).
Findings from two large randomized, placebo-controlled clinical trials, the Calcium Polyp Prevention Study 76), 77) and the European Cancer Prevention Organisation Intervention Study 78) showed that daily supplementation with 1200 to 2000 mg elemental calcium was associated with a reduced risk of recurrence of colorectal polyps known as adenomas in both men and women. Adenomas are thought to be the precursors of most colorectal cancers. In these trials, individuals who previously had one or more large adenomas removed during colonoscopy were randomly assigned to receive calcium supplementation or a placebo, and the rates of polyp recurrence and other factors were compared between the groups.
The Calcium Polyp Prevention Study involved 930 participants who were randomly assigned to receive 3 grams of calcium carbonate (1200 mg elemental calcium) daily for 4 years or a placebo and then receive follow-up colonoscopies approximately 9 months later and again 3 years after that. Compared with those in the placebo group, the individuals assigned to take calcium had about a 20 percent lower risk of adenoma recurrence 79), 80).
The European Cancer Prevention Organisation Intervention Study involved 665 participants who were randomly assigned to one of three treatment groups: 2 grams of elemental calcium daily (from calcium gluconolactate and calcium carbonate), 3 grams of fiber supplementation daily, or a placebo 81). The results showed that calcium supplementation was associated with a modest reduction in the risk of adenoma recurrence, but this finding was not statistically significant.
The results of another clinical trial conducted as part of the Women’s Health Initiative showed that supplementation with 1000 mg elemental calcium (from calcium carbonate) per day for an average duration of 7 years was not associated with a reduced risk of colorectal cancer 82). The calcium supplements in this trial also contained vitamin D (400 international units [IU]). During the trial, 128 cases of invasive colorectal cancer were diagnosed in the supplementation group and 126 cases were diagnosed in the placebo group.
In 2007, the World Cancer Research Fund/American Institute for Cancer Research published the most authoritative review of existing evidence relating food, nutrition, and physical activity to cancer risk. The report concluded that calcium probably has a protective effect against colorectal cancer 83).
The results of some studies suggest that a high calcium intake may decrease the risk of one or more types of cancer, whereas other studies suggest that a high calcium intake may actually increase the risk of prostate cancer.
In a randomized trial that included nearly 1,200 healthy, postmenopausal Nebraska women, individuals were randomly assigned to receive daily calcium supplementation alone (300–600 mg elemental calcium), calcium supplementation (300–600 mg elemental calcium) combined with vitamin D supplementation (1000 IU), or a placebo for 4 years 84). The incidence of all cancers combined was approximately 60 percent lower for women who took the calcium plus vitamin D supplements compared with women who took the placebo. A lower risk of all cancers combined was also observed for women who took calcium supplements alone, but this finding was not statistically significant. The numbers of individual types of cancer diagnosed during this study were too low to be able to draw reliable conclusions about cancer-specific protective effects.
The results of some but not all studies suggest that a high intake of calcium may increase the risk of prostate cancer. For example, the European Prospective Investigation into Cancer and Nutrition analyzed the intakes of animal foods (meat, poultry, fish, dairy products, etc.), protein, and calcium in relation to prostate cancer risk among more than 142,000 men and found that a high intake of protein or calcium from dairy products was associated with an increased risk of prostate cancer 85). Calcium from nondairy sources, however, was not associated with increased risk 86). In addition, a prospective analysis of dairy product and calcium intakes among more than 29,000 men participating in the National Cancer Institute’s Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial showed increased risks for prostate cancer associated with high dietary intakes of calcium and dairy products, particularly low-fat dairy products 87). Calcium from supplements was not associated with increased prostate cancer risk 88). In contrast, results from the NIH-AARP Diet and Health Study showed no increased risk of prostate cancer associated with total calcium, dietary calcium, or supplemental calcium intakes 89), 90).
Other studies have suggested that intakes of low-fat milk, lactose, and calcium from dairy products may reduce the risk of ovarian cancer, but this risk reduction has not been found in all studies 91), 92).
An analysis from the Nurses’ Health Study that included more than 3,000 women found that higher calcium intakes (more than 800 mg per day) from dairy products—particularly low-fat or nonfat milk, yogurt, and cheese—compared with lower calcium intakes (200 mg or less per day) from dairy products was associated with a reduced risk of breast cancer among premenopausal but not postmenopausal women 93). Calcium from nondairy sources was not associated with a reduction in risk 94). Another analysis that involved more than 30,000 women in the Women’s Health Study found a reduced risk of breast cancer associated with higher (1366 mg per day or more) versus lower (less than 617 mg per day) total intakes of calcium among premenopausal but not postmenopausal women 95). In this study, higher versus lower calcium intakes from the diet, from supplements, and from total dairy products were not associated with reduced risk 96).
Calcium has been proposed to help reduce cardiovascular disease (CVD) risk by decreasing intestinal absorption of lipids, increasing lipid excretion, lowering cholesterol levels in the blood, and promoting calcium influx into cells 97). However, data from prospective studies of calcium’s effects on CVD risk are inconsistent, and whether dietary calcium has different effects on the cardiovascular system than supplemental calcium is not clear. In the Iowa Women’s Health Study, higher calcium intake from diet and/or supplements was associated with reduced ischemic heart disease mortality in postmenopausal women 98). Conversely, in a cohort of older Swedish women, both total and dietary calcium intakes of 1,400 mg/day and higher were associated with higher rates of death from CVD and ischemic heart disease than intakes of 600–1,000 mg/day 99). Other prospective studies have shown no significant associations between calcium intake and cardiac events or cardiovascular mortality 100). Data for stroke are mixed, with some studies linking higher calcium intakes to lower risk of stroke, and others finding no associations or trends in the opposite direction 101), 102).
Several studies have raised concerns that calcium from supplements might increase the risk of CVD, including myocardial infarction and coronary heart disease 103), 104), 105), 106). For example, Xiao and colleagues reported that men who took more than 1,000 mg/day supplemental calcium had a 20% higher risk of total CVD death than men who did not take supplemental calcium, but supplemental calcium intake in women was unrelated to CVD mortality 107). A reanalysis of data from the Women’s Health Initiative found that calcium supplements (1,000 mg/day) taken with or without vitamin D (400 IU/day) increased the risk of cardiovascular events in women who were not taking calcium supplements when they entered the study 108). While there is no established biological mechanism to support an association between calcium and CVD, some scientists hypothesize that excessively high calcium intakes from supplements might override normal homeostatic controls of serum calcium levels and produce a temporary hypercalcemia 109), 110), 111). Hypercalcemia is associated with increased blood coagulation, vascular calcification, and arterial stiffness, all of which raise CVD risk 112), 113), 114), 115).
Many scientists question the strength of the available evidence linking supplemental calcium intake with CVD risk, noting that no clinical trials were designed primarily to evaluate this potential relationship, so researchers have only considered CVD outcomes in secondary analyses of trial data 116), 117), 118). Based on a 2016 systematic review and meta-analysis of 4 randomized trials and 27 observational studies 119), the American Society for Preventive Cardiology and the National Osteoporosis Foundation concluded that there is “moderate-quality evidence” that calcium with or without vitamin D (from supplements or foods) “has no relationship (beneficial or harmful) with the risk for cardiovascular and cerebrovascular disease, mortality, or all-cause mortality in generally healthy adults” 120). They added that based on the evidence to date, “calcium intake from food and supplements that does not exceed the [UL] should be considered safe from a cardiovascular standpoint.”
High blood pressure
Some studies have found that getting recommended intakes of calcium can reduce the risk of developing high blood pressure (hypertension). One large study in particular found that eating a diet high in fat-free and low-fat dairy products, vegetables, and fruits lowered blood pressure.
Several clinical trials have demonstrated a relationship between increased calcium intakes and both lower blood pressure and risk of hypertension 121), 122), 123), although the reductions are inconsistent. In the Women’s Health Study, calcium intake was inversely associated with risk of hypertension in middle-aged and older women 124). However, other studies have found no association between calcium intake and incidence of hypertension 125). The authors of a systematic review of the effects of calcium supplements for hypertension found any link to be weak at best, largely due to the poor quality of most studies and differences in methodologies 126).
Calcium’s effects on blood pressure might depend upon the population being studied. In hypertensive subjects, calcium supplementation appears to lower systolic blood pressure by 2–4 mmHg, whereas in normotensive subjects, calcium appears to have no significant effect on systolic or diastolic blood pressure.
Other observational and experimental studies suggest that individuals who eat a vegetarian diet high in minerals (such as calcium, magnesium, and potassium) and fiber and low in fat tend to have lower blood pressure 127), 128), 129), 130), 131). The Dietary Approaches to Stop Hypertension (DASH) study was conducted to test the effects of three different eating patterns on blood pressure: a control “typical” American diet; one high in fruits and vegetables; and a third diet high in fruits, vegetables, and low-fat dairy products. The diet containing dairy products resulted in the greatest decrease in blood pressure 132), although the contribution of calcium to this effect was not evaluated. Additional information and sample DASH menu plans are available on the National Heart, Lung, and Blood Institute Web site 133).
Preeclampsia is a serious medical condition in which a pregnant woman develops high blood pressure and kidney problems that cause protein to spill into the urine. It is a leading cause of sickness and death in pregnant women and their newborn babies. For women who get less than about 900 mg of calcium a day, taking calcium supplements during pregnancy (1,000 mg a day or more) reduces the risk of preeclampsia. But most women in the United States who become pregnant get enough calcium from their diets.
Preeclampsia is a serious medical condition in which a pregnant woman develops hypertension and proteinuria, usually after 20 weeks’ gestation 134). It is a leading cause of maternal and neonatal morbidity and mortality, affecting about 5–8% of pregnancies in the United States and up to 14% of pregnancies worldwide 135), 136).
Studies suggest that calcium supplementation during pregnancy reduces the risk of preeclampsia, but the benefits may apply only to populations with inadequate calcium intakes 137), 138). For example, in a randomized clinical trial among 524 healthy women in India with mean baseline calcium intakes of only 314 mg/day, daily supplementation with 2,000 mg calcium starting between 12 and 25 weeks’ gestation and continuing until delivery significantly reduced the risk of preeclampsia, as well as preterm birth, compared to placebo 139). Conversely, in a randomized trial of 4,589 healthy women in the United States, daily supplementation with 2,000 mg calcium from 13–21 weeks’ gestation through the remainder of pregnancy did not reduce the incidence of preeclampsia, pregnancy-induced hypertension, or other adverse perinatal outcomes compared to placebo 140). The mean baseline calcium intake among these women, however, was about 1,100 mg/day. The authors of a 2014 Cochrane review of 13 clinical trials concluded that daily supplementation with 1,000 mg or more of calcium during pregnancy reduced the risk of preeclampsia by 55% 141). The reduction in risk was greatest for women at high risk of preeclampsia and those with low baseline calcium intakes (less than about 900 mg/day). For women with higher dietary calcium intakes, however, the reduction in preeclampsia risk was not statistically significant.
Several professional organizations recommend calcium supplements during pregnancy for women with low calcium intakes to reduce the risk of preeclampsia. For example, the American College of Obstetrics and Gynecology (ACOG) states that daily supplementation with 1,500–2,000 mg calcium may reduce the severity of preeclampsia in pregnant women who have calcium intakes less than 600 mg/day 142). Similarly, the World Health Organization (WHO) recommends 1,500–2,000 mg calcium for pregnant women with low dietary calcium intakes, particularly those at higher risk of gestational hypertension 143). The WHO recommends dividing the total daily dose into three doses, preferably to be taken at mealtimes, and taking the supplements from 20 weeks’ gestation until delivery. The WHO also recommends separating calcium and prenatal iron supplements by several hours to minimize the inhibitory effects of calcium on iron absorption. But some researchers argue that this interaction has minimal clinical significance and suggest that providers not counsel patients to separate the supplements to simplify the supplement regimen and facilitate adherence 144). The Canadian Hypertensive Disorders of Pregnancy Working Group 145), the International Society for the Study of Hypertension in Pregnancy 146), and the Society of Obstetric Medicine of Australia and New Zealand 147) have all issued similar recommendations to ACOG and the WHO.
Most kidney stones are rich in calcium oxalate. Some studies have found that higher intakes of calcium from dietary supplements are linked to a greater risk of kidney stones, especially among older adults. But calcium from foods does not appear to cause kidney stones. For most people, other factors (such as not drinking enough fluids) probably have a larger effect on the risk of kidney stones than calcium intake.
Kidney stones in the urinary tract are most commonly composed of calcium oxalate. Some, but not all, studies suggest a positive association between supplemental calcium intake and the risk of kidney stones, and these findings were used as the basis for setting the calcium UL in adults. In the Women’s Health Initiative, postmenopausal women who consumed 1,000 mg of supplemental calcium and 400 IU of vitamin D per day for 7 years had a 17% higher risk of kidney stones than subjects taking a placebo 148). The Nurses’ Health Study also showed a positive association between supplemental calcium intake and kidney stone formation 149). High intakes of dietary calcium, on the other hand, do not appear to cause kidney stones and may actually protect against developing them 150), 151), 152), 153), 154). For most individuals, other risk factors for kidney stones, such as high intakes of oxalates from food and low intakes of fluid, probably play a bigger role than calcium intake 155).
Although several studies have shown that getting more calcium helps lower body weight or reduce weight gain over time, most studies have found that calcium—from foods or dietary supplements—has little if any effect on body weight and amount of body fat.
Several studies have linked higher calcium intakes to lower body weight or less weight gain over time 156), 157), 158), 159). Two explanations have been proposed. First, high calcium intakes might reduce calcium concentrations in fat cells by decreasing the production of parathyroid hormone and the active form of vitamin D. Decreased intracellular calcium concentrations in turn increase fat breakdown and discourage fat accumulation in these cells 160). Secondly, calcium from food or supplements might bind to small amounts of dietary fat in the digestive tract and prevent its absorption 161), 162), 163). Dairy products, in particular, might contain additional components that have even greater effects on body weight than their calcium content alone would suggest 164), 165), 166), 167), 168), 169).
Despite these findings, the results from clinical trials have been largely negative. For example, dietary supplementation with 1,500 mg/day of calcium (from calcium carbonate) for 2 years was found to have no clinically significant effects on weight in 340 overweight and obese adults as compared with placebo 170). Three reviews of published studies on calcium from supplements or dairy products on weight management came to similar conclusions 171), 172), 173). A meta-analysis of 13 randomized controlled trials published in 2006 concluded that neither calcium supplementation nor increased dairy product consumption had a statistically significant effect on weight reduction 174). More recently, a 2009 evidence report from the Agency for Healthcare Research and Quality concluded that, overall, clinical trial results do not support an effect of calcium supplementation on weight loss 175). Also, a 2012 meta-analysis of 29 randomized controlled trials found no benefit of an increased consumption of dairy products on body weight and fat loss in long-term studies 176). Overall, the results from clinical trials do not support a link between higher calcium intakes and lower body weight or weight loss.
How much calcium do you need per day ?
Intake recommendations for calcium and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board at the Institute of Medicine of the National Academies 177). Dietary Reference Intake (DRI) is the general term for a set of reference values used for planning and assessing the 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 individuals.
- Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
- Estimated Average Requirement (EAR): average daily level of intake estimated to meet the requirements of 50% of healthy individuals. It is usually used to assess the adequacy of nutrient intakes in populations but not individuals.
- Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects.
The Food and Nutrition Board at the Institute of Medicine of the National Academies established 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 1 in milligrams (mg) per day.
The amount of calcium you need each day depends on your age.
Many people don’t get recommended amounts of calcium from the foods they eat. When total intakes from both food and supplements are considered, many people—particularly adolescent girls—still fall short of getting enough calcium, while some older women likely get more than the upper limit.
People should get most of their nutrients from food, advises the federal government’s Dietary Guidelines for Americans. Foods contain vitamins, minerals, dietary fiber and other substances that benefit health. In some cases, fortified foods and dietary supplements may provide nutrients that otherwise may be consumed in less-than-recommended amounts. For more information about building a healthy diet, refer to the Dietary Guidelines for Americans 178) and the U.S. Department of Agriculture’s MyPlate 179).
Table 1. Average calcium daily recommended amounts are listed below in milligrams (mg)
|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 180) ]
What foods provide calcium?
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).
Calcium Rich Foods
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 181). 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 2.
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 182). 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 2. 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 183)]
Inadequate intakes of dietary calcium from food and supplements produce no obvious symptoms in the short term. Circulating blood levels of calcium are tightly regulated. Hypocalcemia results primarily from medical problems or treatments, including renal failure, surgical removal of the stomach, and use of certain medications (such as diuretics). Symptoms of hypocalcemia include numbness and tingling in the fingers, muscle cramps, convulsions, lethargy, poor appetite, and abnormal heart rhythms 184). If left untreated, calcium deficiency leads to death.
Over the long term, inadequate calcium intake causes osteopenia which if untreated can lead to osteoporosis. The risk of bone fractures also increases, especially in older individuals. Calcium deficiency can also cause rickets, though it is more commonly associated with vitamin D deficiency.
Certain groups of people are more likely than others to have trouble getting enough calcium:
- Postmenopausal women because they experience greater bone loss and do not absorb calcium as well. Sufficient calcium intake from food, and supplements if needed, can slow the rate of bone loss.
Menopause leads to bone loss because decreases in estrogen production both increase bone resorption and decrease calcium absorption. Annual decreases in bone mass of 3%–5% per year frequently occur in the first years of menopause, but the decreases are typically less than 1% per year after age 65 185). Increased calcium intakes during menopause do not completely offset this bone loss 186), 187). Hormone replacement therapy (HRT) with estrogen and progesterone helps increase calcium levels and prevent osteoporosis and fractures. Estrogen therapy restores postmenopausal bone remodeling to the same levels as at premenopause, leading to lower rates of bone loss 188), perhaps in part by increasing calcium absorption in the gut. Several medical groups and professional societies support the use of HRT as an option for women who are at increased risk of osteoporosis or fractures 189), 190), 191). Such women should discuss this matter with their health care providers. In addition, consuming adequate amounts of calcium in the diet might help slow the rate of bone loss in all women.
- Women of childbearing age whose menstrual periods stop (amenorrhea) because they exercise heavily, eat too little, or both. They need sufficient calcium to cope with the resulting decreased calcium absorption, increased calcium losses in the urine, and slowdown in the formation of new bone.
Amenorrhea, the condition in which menstrual periods stop or fail to initiate in women of childbearing age, results from reduced circulating estrogen levels that, in turn, have a negative effect on calcium balance. Amenorrheic women with anorexia nervosa have decreased calcium absorption and higher urinary calcium excretion rates, as well as a lower rate of bone formation than healthy women 192). The “female athlete triad” refers to the combination of disordered eating, amenorrhea, and osteoporosis. Exercise-induced amenorrhea generally results in decreased bone mass 193), 194). In female athletes and active women in the military, low bone-mineral density, menstrual irregularities, certain dietary patterns, and a history of prior stress fractures are associated with an increased risk of future stress fractures 195). Such women should be advised to consume adequate amounts of calcium and vitamin D. Supplements of these nutrients have been shown to reduce the risk of stress fractures in female Navy recruits during basic training 196).
- People with lactose intolerance cannot digest this natural sugar found in milk and experience symptoms like bloating, gas, and diarrhea when they drink more than small amounts at a time. They usually can eat other calcium-rich dairy products that are low in lactose, such as yogurt and many cheeses, and drink lactose-reduced or lactose-free milk.
Lactose intolerance refers to symptoms (such as bloating, flatulence, and diarrhea) that occur when one consumes more lactose, the naturally occurring sugar in milk, than the enzyme lactase produced by the small intestine can hydrolyze into its component monosaccharides, glucose and galactose 197). The symptoms vary, depending on the amount of lactose consumed, history of consumption of lactose-containing foods, and type of meal. Although the prevalence of lactose intolerance is difficult to discern 198), some reports suggest that approximately 25% of U.S. adults have a limited ability to digest lactose, including 85% of Asians, 50% of African Americans, and 10% of Caucasians 199), 200), 201).
Lactose-intolerant individuals are at risk of calcium inadequacy if they avoid dairy products. Research suggests that most people with lactose intolerance can consume up to 12 grams of lactose, such as that present in 8 ounces of milk, with minimal or no symptoms, especially if consumed with other foods; larger amounts can frequently be consumed if spread over the day and eaten with other foods. Other options to reduce symptoms include eating low-lactose dairy products including aged cheeses (such as Cheddar and Swiss), yogurt, or lactose-reduced or lactose-free milk. Some studies have examined whether it is possible to induce adaptation by consuming incremental lactose loads over a period of time 202), 203), but the evidence in support of this strategy is inconsistent 204).
Cow’s milk allergy is less common than lactose intolerance, affecting 0.6% to 0.9% of the population 205). People with this condition are unable to consume any products containing cow’s milk proteins and are therefore at higher risk of obtaining insufficient calcium.
To ensure adequate calcium intakes, lactose-intolerant individuals and those with cow’s milk allergy can choose nondairy food sources of the nutrient (such as kale, bok choy, Chinese cabbage, broccoli, collards and fortified foods) or take a calcium supplement.
- Vegans (vegetarians who eat no animal products) and ovo-vegetarians (vegetarians who eat eggs but no dairy products), because they avoid the dairy products that are a major source of calcium in other people’s diets.
Vegetarians might absorb less calcium than omnivores because they consume more plant products containing oxalic and phytic acids. Lacto-ovo vegetarians (who consume eggs and dairy) and nonvegetarians have similar calcium intakes 206), 207). However, vegans, who eat no animal products and ovo-vegetarians (who eat eggs but no dairy products), might not obtain sufficient calcium because of their avoidance of dairy foods 208), 209). In the Oxford cohort of the European Prospective Investigation into Cancer and Nutrition, bone fracture risk was similar in meat eaters, fish eaters and vegetarians, but higher in vegans, likely due to their lower mean calcium intake 210). It is difficult to assess the impact of vegetarian diets on calcium status because of the wide variety of eating practices and thus should be considered on a case by case basis.
What happens if you don’t get enough calcium ?
Insufficient intakes of calcium do not produce obvious symptoms in the short term because the body maintains calcium levels in the blood by taking it from bone. Over the long term, intakes of calcium below recommended levels have health consequences, such as causing low bone mass (osteopenia) and increasing the risks of osteoporosis and bone fractures.
Symptoms of serious calcium deficiency include numbness and tingling in the fingers, convulsions, and abnormal heart rhythms that can lead to death if not corrected. These symptoms occur almost always in people with serious health problems or who are undergoing certain medical treatments.
Calcium as Medicines
Because of its ability to neutralize stomach acid, calcium carbonate is found in some over-the-counter antacid products, such as Tums® and Rolaids®. Depending on its strength, each chewable pill or softchew provides 200 to 400 mg of elemental calcium. As noted above, calcium carbonate is an acceptable form of supplemental calcium, especially for individuals who have normal levels of stomach acid 211).
Can too much calcium be harmful ?
Getting too much calcium can cause constipation. It might also interfere with the body’s ability to absorb iron and zinc, but this effect is not well established. In adults, too much calcium (from dietary supplements but not food) might increase the risk of kidney stones. Some studies show that people who consume high amounts of calcium might have increased risks of prostate cancer and heart disease, but more research is needed to understand these possible links.
Most people do not get amounts above the upper limits from food alone; excess intakes usually come from the use of calcium supplements. Surveys show that some older women in the United States probably get amounts somewhat above the upper limit since the use of calcium supplements is common among these women.
Health Risks from Excessive Calcium
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 212). Although very high calcium intakes have the potential to cause hypercalcemia 213), it is most commonly associated with primary hyperparathyroidism or malignancy 214).
High calcium intake can cause constipation. It might also interfere with the absorption of iron and zinc, though this effect is not well established 215). High intake of calcium from supplements, but not foods, has been associated with increased risk of kidney stones 216), 217), 218). 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 219). Some studies also link high calcium intake, particularly from supplements, with increased risk of cardiovascular disease 220), 221), 222), 223), 224), 225).
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 226). Some studies also link high calcium intake, particularly from supplements, with increased risk of cardiovascular disease 227), 228).
The Tolerable Upper Intake Levels (ULs) for calcium established by the Food and Nutrition Board are listed in Table 3 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. 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 229).
Table 3. 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|
What causes high blood calcium ?
The most common cause of high blood calcium is a condition called primary hyperparathyroidism. In this condition, one or more of the parathyroid glands produces too much PTH. This, in turn, causes the bones to release too much calcium into the blood. Women over the age of 50 are more likely than others to have primary hyperparathyroidism.
Certain types of cancer, most often breast cancer, lung cancer, or multiple myeloma (a type of blood cancer), can also cause high blood calcium. This usually occurs late in the course of cancer.
Less common causes of hypercalcemia include these health problems:
- Some types of infectious diseases, such as tuberculosis (TB)
- Some types of autoimmune disease, such as sarcoidosis
- Hormone disorders, such as overactive thyroid (hyperthyroidism)
- A genetic condition called familial hypocalciuric hypercalcemia
- Kidney failure
Other infrequent causes of high blood calcium include:
- Some medicines, such as lithium (to treat psychiatric illness) or rarely, thiazide diuretics
- Intake of very large amounts of calcium or large amounts of milk plus antacids
- Intake of too much vitamin D or vitamin A
- Immobility–being confined to bed for at least several weeks– combined with some bone diseases, such as Paget’s disease
- Tube feeding or being fed through a vein
- Severe dehydration
How is high blood calcium treated ?
Talk with your health care provider about the best treatment for your condition. Your treatment will depend on the cause of your high blood
calcium. In general, the best treatment is to take care of the condition that is causing the high blood calcium. For instance, people with primary hyperparathyroidism who have symptoms usually have surgery to remove the problem-causing parathyroid gland.
Until the underlying problem is resolved, treatment may include medicines to improve blood calcium levels. When blood calcium is dangerously high, people may need treatment in a hospital to return their blood calcium to a safe level.
You might not need any treatment if your blood calcium is only slightly high or you have not developed any health problems. Instead, your health care provider will continue to check your condition over time.
Other Forms of Calcium
- Calcium Gluconate
Calcium Gluconate injection treats too little calcium in the blood. Also treats black widow spider bites, lead colic, overdose of magnesium or certain heart medicines, and rickets. This medicine is also used for life support and life-threatening heart conditions 231).
- Calcium Oxide
Materials used in the production of dental bases, restorations, impressions, prostheses, etc. Nano-thick calcium oxide armed titanium: boosts bone cells against methicillin-resistant Staphylococcus aureus (MRSA) in rabbits 232).
- Calcium Phosphate
Synthetic bio-inert materials are currently used as an alternative to autogenous bone graft. Calcium hydroxyapatite (HA) and Beta tri-calcium phosphate (β-TCP), which belong to the calcium phosphate ceramics group, are biocompatible and osteo-conductive. Calcium hydroxyapatite and β-TCP are excellent bone graft substitutes for autogenous bone graft in filling voids after curettage of benign bone tumors 233). Calcium phosphate is also used as gastric antacid 234).
- Calcium Sulfate
The use of calcium sulfate (plaster of Paris) has been advocated to repair bony defects because of its unique capability of stimulating osteoneogenesis. Plaster of Paris can be used as a bony alloplast, and it can be analyzed histologically. Sinus roentgenograms and technetium Tc 99m medronate bone scanning further support the use of plaster of Paris as an alloplast and assess its osteoneogenic capacity when implanted in the frontal sinus of dogs; complete bone regeneration was demonstrated in six dogs within four to six months. The use of plaster of Paris for bone reconstruction in the head and neck can be applied in surgery. The experience with plaster of Paris to date, although limited, shows it to be safe and highly encouraging as an effective bone allograft 235)).
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