zinc foods

What is Zinc

Zinc is an essential mineral that is naturally present in some foods, added to others, and available as a dietary supplement. Zinc is also found in many cold lozenges and some over-the-counter drugs sold as cold remedies. Zinc is a nutrient that people need to stay healthy. A daily intake of zinc is required to maintain a steady state because the body has no specialized zinc storage system 1).

Zinc is found in cells throughout the body, found mainly in bones, teeth, hair, skin, liver, muscle, leukocytes, and testes 2). Zinc helps the immune system fight off invading bacteria and viruses. The body also needs zinc to make proteins and DNA, the genetic material in all cells. During pregnancy, infancy, and childhood, the body needs zinc to grow and develop properly. Zinc also helps wounds heal and is important for proper senses of taste and smell.

Zinc is involved in numerous aspects of cellular metabolism. It is required for the catalytic activity of approximately 100 enzymes 3) and it plays a role in immune function 4), protein synthesis 5), wound healing 6), DNA synthesis 7), and cell division 8). Zinc also supports normal growth and development during pregnancy, childhood, and adolescence 9) and is required for proper sense of taste and smell 10).

Most Americans get enough zinc from the foods they eat.

However, certain groups of people are more likely than others to have trouble getting enough zinc:

  • People who have had gastrointestinal surgery, such as weight loss surgery, or who have digestive disorders, such as ulcerative colitis or Crohn’s disease. These conditions can both decrease the amount of zinc that the body absorbs and increase the amount lost in the urine.
  • Vegetarians because they do not eat meat, which is a good source of zinc. Also, the beans and grains they typically eat have compounds that keep zinc from being fully absorbed by the body. For this reason, vegetarians might need to eat as much as 50% more zinc than the recommended amounts.
  • Older infants who are breastfed because breast milk does not have enough zinc for infants over 6 months of age. Older infants who do not take formula should be given foods that have zinc such as pureed meats. Formula-fed infants get enough zinc from infant formula.
  • Alcoholics because alcoholic beverages decrease the amount of zinc that the body absorbs and increase the amount lost in the urine. Also, many alcoholics eat a limited amount and variety of food, so they may not get enough zinc.
  • People with sickle cell disease because they might need more zinc.

Clinical zinc deficiency in humans was first described in 1961, when the consumption of diets with low zinc bioavailability due to high phytate content was associated with “adolescent nutritional dwarfism” in the Middle East 11). Since then, zinc insufficiency has been recognized by a number of experts as an important public health issue, especially in low-resource countries 12). Severe zinc deficiency is rare and caused by an inherited condition called acrodermatitis enteropathica. Acquired zinc deficiency is primarily due to malabsorption syndromes and chronic alcoholism.

Currently, there is not a sensitive and specific biomarker to detect zinc deficiency in humans. Low plasma or serum zinc concentrations are typically used as indicators of zinc status in populations and in intervention studies, but they have a number of limitations, including lack of sensitivity to detect marginal zinc deficiency, diurnal variations, and confounding by inflammation, stress, and hormones 13).

Zinc key points

  • Zinc is a nutritionally essential mineral needed for catalytic, structural, and regulatory functions in the body.
  • Severe zinc deficiency is rare and caused by an inherited condition called acrodermatitis enteropathica. Acquired zinc deficiency is primarily due to malabsorption syndromes and chronic alcoholism.
  • Dietary zinc deficiency is quite common in the developing world, affecting an estimated 2 billion people. Consumption of diets high in phytate and lacking foods from animal origin drive zinc deficiency in these populations.
  • The recommended dietary allowance (RDA) for adult men and women is 11 mg/day and 8 mg/day of zinc, respectively.
  • Long-term consumption of zinc in excess of the tolerable upper intake level (UL) is 40 mg/day for adults) can result in copper deficiency.
  • Dietary zinc deficiency has been associated with impaired growth and development in children, pregnancy complications, and immune dysfunction with increased susceptibility to infections.
  • Supplementation with doses of zinc in excess of the upper intake level (UL) is effective to reduce the duration of common cold symptoms. The use of zinc at daily doses of 50 to 180 mg for one to two weeks has not resulted in serious side effects.
  • Current evidence suggests that supplemental zinc may be useful in the management of chronic conditions, such as age-related macular degeneration, diabetes mellitus, Wilson’s disease, and HIV/AIDS.
  • Zinc bioavailability is relatively high in meat, eggs, and seafood; zinc is less bioavailable from whole grains and legumes due to their high content in phytate that inhibits zinc absorption.

What Does Zinc Do

Zinc is an essential mineral that is naturally present in some foods, added to others, and available as a dietary supplement. Zinc is also found in many cold lozenges and some over-the-counter drugs sold as cold remedies.

Zinc is involved in numerous aspects of cellular metabolism. It is required for the catalytic activity of approximately 100 enzymes, including many nicotinamide adenine dinucleotide (NADH) dehydrogenases, RNA and DNA polymerases, and DNA transcription factors as well as alkaline phosphatase, superoxide dismutase, and carbonic anhydrase 14), 15) and it plays a role in immune function 16), 17), protein synthesis 18), wound healing 19), DNA synthesis 20), 21) and cell division 22). Zinc also supports normal growth and development during pregnancy, childhood, and adolescence 23), 24), 25) and is required for proper sense of taste and smell 26). A daily intake of zinc is required to maintain a steady state because the body has no specialized zinc storage system 27).

Zinc supplements

Supplements contain several forms of zinc, including zinc gluconate, zinc sulfate, and zinc acetate 28). The percentage of elemental zinc varies by form. For example, approximately 23% of zinc sulfate consists of elemental zinc; thus, 220 mg of zinc sulfate contains 50 mg of elemental zinc. The elemental zinc content appears in the Supplement Facts panel on the supplement container. Research has not determined whether differences exist among forms of zinc in absorption, bioavailability, or tolerability 29).

In addition to standard tablets and capsules, some zinc-containing cold lozenges are labeled as dietary supplements.

Are there any interactions with zinc that I should know about?

Yes. Zinc dietary supplements can interact or interfere with medicines that you take and, in some cases, medicines can lower zinc levels in the body. Here are several examples:

  • Taking a zinc dietary supplement along with quinolone or tetracycline antibiotics (such as Cipro®, Achromycin®, and Sumycin®) reduces the amount of both zinc and the antibiotic that the body absorbs. Taking the antibiotic at least 2 hours before or 4–6 hours after taking a zinc dietary supplement helps minimize this effect.
  • Zinc dietary supplements can reduce the amount of penicillamine (a drug used to treat rheumatoid arthritis) that the body absorbs. They also make penicillamine work less well. Taking zinc dietary supplements at least 2 hours before or after taking penicillamine helps minimize this effect.
  • Thiazide diuretics, such as chlorthalidone (brand name Hygroton®) and hydrochlorothiazide (brand names Esidrix® and HydroDIURIL®) increase the amount of zinc lost in the urine. Taking thiazide diuretics for a long time could decrease the amount of zinc in the body.

Tell your doctor, pharmacist, and other healthcare providers about any dietary supplements and medicines you take. They can tell you if those dietary supplements might interact or interfere with your prescription or over-the-counter medicines or if the medicines might interfere with how your body absorbs, uses, or breaks down nutrients.

Interactions with iron and copper

Iron-deficiency anemia is a serious world-wide public health problem. Iron fortification programs have been credited with improving the iron status of millions of women, infants, and children. Fortification of foods with iron does not significantly affect zinc absorption. However, large amounts of supplemental iron (greater than 25 mg) might decrease zinc absorption 30). Taking iron supplements between meals helps decrease its effect on zinc absorption 31).

High zinc intakes can inhibit copper absorption, sometimes producing copper deficiency and associated anemia 32), 33). For this reason, dietary supplement formulations containing high levels of zinc, such as the one used in the Age-Related Eye Disease Study Research Group (AREDS) study 34), sometimes contain copper.

Other Sources of Zinc

Zinc is present in several products, including some labeled as homeopathic medications, sold over the counter for the treatment and prevention of colds. Numerous case reports of anosmia (loss of the sense of smell), in some cases long-lasting or permanent, have been associated with the use of zinc-containing nasal gels or sprays 35), 36). In June 2009, the FDA warned consumers to stop using three zinc-containing intranasal products because they might cause anosmia 37). The manufacturer recalled these products from the marketplace. Currently, these safety concerns have not been found to be associated with cold lozenges containing zinc.

Zinc is also present in some denture adhesive creams at levels ranging from 17–34 mg/g 38). While use of these products as directed (0.5–1.5 g/day) is not of concern, chronic, excessive use can lead to zinc toxicity, resulting in copper deficiency and neurologic disease. Such toxicity has been reported in individuals who used 2 or more standard 2.4 oz tubes of denture cream per week 39), 40). Many denture creams have now been reformulated to eliminate zinc.

zinc foods

Benefits of Zinc on Health 

Age-related macular degeneration (AMD)

Researchers have suggested that both zinc and antioxidants delay the progression of age-related macular degeneration (AMD) and vision loss, possibly by preventing cellular damage in the retina 41), 42). In a population-based cohort study in the Netherlands, high dietary intake of zinc as well as beta carotene, vitamin C, and vitamin E was associated with reduced risk of AMD in elderly subjects 43). However, the authors of a systematic review and meta-analysis published in 2007 concluded that zinc is not effective for the primary prevention of early AMD 44), although zinc might reduce the risk of progression to advanced AMD.

The Age-Related Eye Disease Study (AREDS), a large, randomized, placebo-controlled, clinical trial (n = 3,597), evaluated the effect of high doses of selected antioxidants (500 mg vitamin C, 400 IU vitamin E, and 15 mg beta-carotene) with or without zinc (80 mg as zinc oxide) on the development of advanced AMD in older individuals with varying degrees of AMD 45). Participants also received 2 mg copper to prevent the copper deficiency associated with high zinc intakes. After an average follow-up period of 6.3 years, supplementation with antioxidants plus zinc (but not antioxidants alone) significantly reduced the risk of developing advanced AMD and reduced visual acuity loss. Zinc supplementation alone significantly reduced the risk of developing advanced AMD in subjects at higher risk but not in the total study population. Visual acuity loss was not significantly affected by zinc supplementation alone. A follow-up AREDS2 study confirmed the value of this supplement in reducing the progression of AMD over a median follow-up period of 5 years 46). Importantly, AREDS2 revealed that a formulation providing 25 mg zinc (about one-third the amount in the original AREDS formulation) provided the same protective effect against developing advanced AMD.

Two other small clinical trials evaluated the effects of supplementation with 200 mg zinc sulfate (providing 45 mg zinc) for 2 years in subjects with drusen or macular degeneration. Zinc supplementation significantly reduced visual acuity loss in one of the studies 47) but had no effect in the other 48).

A Cochrane review concluded that the evidence supporting the use of antioxidant vitamins and zinc for AMD comes primarily from the AREDS study 49). Individuals who have or are developing AMD should talk to their health care provider about taking a zinc-containing AREDS supplement.

Common cold

The common cold is often caused by the rhinovirus. It is one of the most widespread illnesses and is a leading cause of visits to the doctor and absenteeism from school and work. Complications of the common cold include otitis media (middle ear infection), sinusitis and exacerbations of reactive airway diseases 50). There is no proven treatment for the common cold 51). However, a medication that is even partially effective in the treatment and prevention of the common cold could markedly reduce morbidity and economic losses due to this illness.

Zinc, which can inhibit rhinovirus replication in test tube studies and has activity against other respiratory viruses such as respiratory syncytial virus 52). The exact mechanism of zinc’s activity on viruses remains uncertain. Zinc may also reduce the severity of cold symptoms by acting as an astringent on the trigeminal nerve 53).

There’s been a lot of talk about taking zinc for colds ever since a 1984 study 54) showed that zinc supplements kept people from getting as sick. Since then, research has turned up mixed results about zinc and colds – failure of zinc gluconate in treatment of acute upper respiratory tract infections 55), 56), 57) and a positive result for zinc in the treatment for common colds 58), 59), 60), 61).

In a randomized, double-blind, placebo-controlled clinical trial, 50 subjects (within 24 hours of developing the common cold) took a zinc acetate lozenge (13.3 mg zinc) or placebo every 2–3 wakeful hours. Compared with placebo, the zinc lozenges significantly reduced the duration of cold symptoms (cough, nasal discharge, and muscle aches) 62).

A meta-analysis of seven trials recently reported a 33% reduction in the duration of cold symptoms with the intake of zinc lozenges (>75 mg/day of elemental zinc) 63). However, many supplemental zinc formulations available over-the-counter have been found to release zero zinc ions (i.e., the biologically active form of zinc) or to contain additives (e.g., magnesium, certain amino acids, citric acid) that either cancel out the benefit of zinc or worsen cold symptoms 64).

In addition, although taking zinc lozenges for a cold every two to three hours while awake will result in daily zinc intakes well above the tolerable upper intake level (UL) of 40 mg/day for adults, the use of zinc at daily doses of 50 to 180 mg for one to two weeks has not resulted in serious side effects 65). Bad taste and nausea were the most frequent adverse effects reported in therapeutic trials 66). Use of zinc lozenges for prolonged periods (e.g., 6-8 weeks) is likely to result in copper deficiency.

In another clinical trial involving 273 participants with experimentally induced colds, zinc gluconate lozenges (providing 13.3 mg zinc) significantly reduced the duration of illness compared with placebo but had no effect on symptom severity 67). However, treatment with zinc acetate lozenges (providing 5 or 11.5 mg zinc) had no effect on either cold duration or severity. Neither zinc gluconate nor zinc acetate lozenges affected the duration or severity of cold symptoms in 281 subjects with natural (not experimentally induced) colds in another trial 68).

In 77 participants with natural colds, a combination of zinc gluconate nasal spray and zinc orotate lozenges (37 mg zinc every 2–3 wakeful hours) was also found to have no effect on the number of asymptomatic patients after 7 days of treatment 69).

In September of 2007, Caruso and colleagues published a structured review of the effects of zinc lozenges, nasal sprays, and nasal gels on the common cold 70). Of the 14 randomized, placebo-controlled studies included, 7 (5 using zinc lozenges, 2 using a nasal gel) showed that the zinc treatment had a beneficial effect and 7 (5 using zinc lozenges, 1 using a nasal spray, and 1 using lozenges and a nasal spray) showed no effect.

As previously noted, the safety of intranasal zinc has been called into question because of numerous reports of anosmia (loss of smell), in some cases long-lasting or permanent, from the use of zinc-containing nasal gels or sprays 71), 72), 73).

Recently analyses of several studies 74), 75), 76) showed that zinc lozenges or syrup reduced the length of a cold by one day, especially when taken within 24 hours of the first signs and symptoms of a cold. In a 2015 meta-analysis by Hemilä and Chalker 77) showed that zinc acetate lozenges shortened the duration of nasal discharge by 34%, nasal congestion by 37% , sneezing by 22%, scratchy throat by 33%, sore throat by 18%, hoarseness by 43% and cough by 46%. Zinc lozenges shortened the duration of muscle ache by 54%, but there was no difference in the duration of headache and fever 78). The same authors concluded that the effect of zinc acetate lozenges on cold symptoms may be associated with the local availability of zinc from the lozenges, with the levels being highest in the pharyngeal region 79). However their findings indicate that the effects of zinc ions are not limited to the pharyngeal region. There is no indication that the effect of zinc lozenges on nasal symptoms is less than the effect on the symptoms of the pharyngeal region, which is more exposed to released zinc ions. In some zinc lozenge trials the lozenges caused short-term adverse effects, such as bad taste, nausea, constipation, diarrhea, abdominal pain, dry mouth and oral irritation, but the bad taste can be explained by the specific lozenge composition and does not necessarily reflect the effects of zinc ions themselves 80). None of the high dose zinc acetate lozenge trials reported bad taste to be a problem and there was no substantial difference between the zinc and placebo groups in the recorded adverse effects, and only a few drop-outs occurred 81). Furthermore, if a common cold patient suffers from acute adverse effects such as bad taste, the patient can simply stop taking the zinc acetate lozenges. Given that the adverse effects of zinc in the 3 trials were minor, zinc acetate lozenges releasing zinc ions at doses of about 80 mg/day may be a useful treatment for the common cold, started within 24 hours, for a time period of less than two weeks 82).

In the USA, the recommended dietary zinc intake is 11 mg/day for men and 8 mg/day for women 83). Thus, the 80 to 92 mg/day doses used in the zinc acetate lozenge trials are substantially higher than the recommended daily intakes. However, in several clinical trials zinc has been administered to patients at a dose of 150 mg/day for months 84). A decrease in copper levels and hematological changes have been reported as adverse effects of long-term high dose zinc administration, but those changes were completely reversed with the cessation of zinc intake 85), 86), 87), 88). Thus, given that 150 mg/day of zinc administration for months does not cause permanent harm, it seems plausible that the use of about 80 mg/day of zinc for up to two weeks in the form of zinc acetate lozenges is unlikely to cause serious adverse effects.

But the recent analysis stopped short of recommending zinc. None of the studies analyzed had enough participants to meet a high standard of proof. Also, the studies used different zinc dosages and preparations (lozenges or syrup) for different lengths of time. As a result, it’s not clear what the effective dose and treatment schedule would be.

Most colds are caused by a type of virus called rhinovirus, which thrives and multiplies in the nasal passages and throat (upper respiratory system). Zinc may work by preventing the rhinovirus from multiplying. It may also stop the rhinovirus from lodging in the mucous membranes of the throat and nose.

Zinc may be more effective when taken in lozenge or syrup form, which allows the substance to stay in the throat and come in contact with the rhinovirus.

Zinc — especially in lozenge form — also has side effects, including nausea or a bad taste in the mouth. Many people who used zinc nasal sprays suffered a permanent loss of smell. For this reason, Mayo Clinic doctors caution against using such sprays.

In addition, large amounts of zinc are toxic and can cause copper deficiency, anemia and damage to the nervous system.

For now, the safest course is to talk to your doctor before considering the use of zinc to prevent or reduce the length of colds.

Zinc supplementation for the prevention of pneumonia in children aged two to 59 months

Recent Cochrane Review published 4th December 2016, showed that zinc supplementation was significantly associated with reducing the incidence and prevalence of pneumonia among children aged from two to 59 months 89).

Diarrhea in children

Children in developing countries often die from diarrhea. Studies show that zinc dietary supplements help reduce the symptoms and duration of diarrhea in these children, many of whom are zinc deficient or otherwise malnourished. The World Health Organization and UNICEF recommend that children with diarrhea take zinc for 10–14 days (20 mg/day, or 10 mg/day for infants under 6 months). It is not clear whether zinc dietary supplements can help treat diarrhea in children who get enough zinc, such as most children in the United States.

Acute diarrhea is associated with high rates of mortality among children in developing countries 90). Zinc deficiency causes alterations in immune response that probably contribute to increased susceptibility to infections, such as those that cause diarrhea, especially in children 91).

Studies show that poor, malnourished children in India, Africa, South America, and Southeast Asia experience shorter courses of infectious diarrhea after taking zinc supplements 92). The children in these studies received 4–40 mg of zinc a day in the form of zinc acetate, zinc gluconate, or zinc sulfate 93).

In addition, results from a pooled analysis of randomized controlled trials of zinc supplementation in developing countries suggest that zinc helps reduce the duration and severity of diarrhea in zinc-deficient or otherwise malnourished children 94). Similar findings were reported in a meta-analysis published in 2008 and a 2007 review of zinc supplementation for preventing and treating diarrhea 95), 96). The effects of zinc supplementation on diarrhea in children with adequate zinc status, such as most children in the United States, are not clear.

The World Health Organization and UNICEF now recommend short-term zinc supplementation (20 mg of zinc per day, or 10 mg for infants under 6 months, for 10–14 days) to treat acute childhood diarrhea 97).

In a 2016 Cochrane Review 98) involving thirty-three trials that included 10,841 children, among children with acute diarrhoea, the authors don’t know if treating children with zinc has an effect on death or number of children hospitalized (very low certainty evidence). In children older than six months, zinc supplementation may shorten the average duration of diarrhoea by around half a day (low certainty evidence), and probably reduces the number of children whose diarrhoea persists until day seven (moderate certainty evidence). In children with signs of malnutrition the effect appears greater, reducing the duration of diarrhoea by around a day (high certainty evidence). Conversely, in children younger than six months, the available evidence suggests zinc supplementation may have no effect on the mean duration of diarrhoea (low certainty evidence), or the number of children who still have diarrhoea on day seven (low certainty evidence). Zinc supplementation increased the risk of vomiting in both age groups (moderate certainty evidence). Among children with persistent diarrhoea, zinc supplementation probably shortens the average duration of diarrhoea by around 16 hours (moderate certainty) but it probably increases the risk of vomiting (moderate certainty evidence). The review authors concluded that zinc supplementation may be of benefit in children aged six months or more, in areas where the prevalenceof zinc deficiency or the prevalence of malnutrition is high 99). In addition, the current evidence does not support the use of zinc supplementation in children less six months of age, in well-nourished children, and in settings where children are at low risk of zinc deficiency 100).

Wound healing

Zinc helps maintain the integrity of skin and mucosal membranes 101). Patients with chronic leg ulcers have abnormal zinc metabolism and low serum zinc levels [56], and clinicians frequently treat skin ulcers with zinc supplements 102). The authors of a systematic review concluded that zinc sulfate might be effective for treating leg ulcers in some patients who have low serum zinc levels 103), 104). However, research has not shown that the general use of zinc sulfate in patients with chronic leg ulcers or arterial or venous ulcers is effective 105).

Immune system

Severe zinc deficiency depresses immune function 106), and even mild to moderate degrees of zinc deficiency can impair macrophage and neutrophil functions, natural killer cell activity, and complement activity 107). The body requires zinc to develop and activate T-lymphocytes 108), 109). Individuals with low zinc levels have shown reduced lymphocyte proliferation response to mitogens and other adverse alterations in immunity that can be corrected by zinc supplementation 110), 111). These alterations in immune function might explain why low zinc status has been associated with increased susceptibility to pneumonia and other infections in children in developing countries and the elderly 112), 113), 114), 115).

How much zinc do you need?

Intake recommendations for zinc 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 116). Dietary Reference Intake is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and gender 117), include the following:

  • 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.
  • Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects 118).

The current RDAs for zinc are listed in Table 1 119). For infants aged 0 to 6 months, the FNB established an AI for zinc that is equivalent to the mean intake of zinc in healthy, breastfed infants.

Table 1. The amount of zinc you need each day depends on your age. Average daily recommended amounts for different ages are listed below in milligrams (mg):

Life StageRecommended Amount
Birth to 6 months2 mg
Infants 7–12 months3 mg
Children 1–3 years3 mg
Children 4–8 years5 mg
Children 9–13 years8 mg
Teens 14–18 years (boys)11 mg
Teens 14–18 years (girls)9 mg
Adults (men)11 mg
Adults (women)8 mg
Pregnant teens12 mg
Pregnant women11 mg
Breastfeeding teens13 mg
Breastfeeding women12 mg

Most infants (especially those who are formula fed), children, and adults in the United States consume recommended amounts of zinc according to two national surveys, the 1988–1991 National Health and Nutrition Examination Survey 120) and the 1994 Continuing Survey of Food Intakes of Individuals 121).

However, some evidence suggests that zinc intakes among older adults might be marginal. An analysis of National Health and Nutrition Examination Survey data found that 35%–45% of adults aged 60 years or older had zinc intakes below the estimated average requirement of 6.8 mg/day for elderly females and 9.4 mg/day for elderly males. When the investigators considered intakes from both food and dietary supplements, they found that 20%–25% of older adults still had inadequate zinc intakes 122).

Zinc intakes might also be low in older adults from the 2%–4% of U.S. households that are food insufficient (sometimes or often not having enough food) 123). Data from National Health and Nutrition Examination Survey indicate that adults aged 60 years or older from food-insufficient families had lower intakes of zinc and several other nutrients and were more likely to have zinc intakes below 50% of the RDA on a given day than those from food-sufficient families 124).

foods high in zinc

What foods provide zinc?

Zinc is found in a wide variety of foods. You can get recommended amounts of zinc by eating a variety of foods including the following:

  • Oysters, which are the best source of zinc. Oysters contain more zinc per serving than any other food.
  • Red meat, poultry, seafood such as crab and lobsters, and fortified breakfast cereals, which are also good sources of zinc. They provide the majority of zinc in the American diet.
  • Beans, nuts, whole grains, and dairy products, which provide some zinc.

Phytates (is the principal storage form of phosphorus in many plant tissues, especially bran and seeds), which are present in whole-grain breads, cereals, legumes, and other foods—bind zinc and inhibit its absorption 125), 126), 127). Thus, the bioavailability of zinc from grains and plant foods is lower than that from animal foods, although many grain- and plant-based foods are still good sources of zinc 128).

The U.S. Department of Agriculture’s (USDA’s) Nutrient Database website (https://fdc.nal.usda.gov) lists the nutrient content of many foods and provides a comprehensive list of foods containing zinc arranged by nutrient content (https://ods.od.nih.gov/pubs/usdandb/Zinc-Content.pdf) and by food name (https://ods.od.nih.gov/pubs/usdandb/Zinc-Food.pdf).

Table 2: Selected Food Sources of Zinc

FoodMilligrams (mg)
per serving
Percent DV*
Oysters, cooked, breaded and fried, 3 ounces74.0493
Beef chuck roast, braised, 3 ounces7.047
Crab, Alaska king, cooked, 3 ounces6.543
Beef patty, broiled, 3 ounces5.335
Breakfast cereal, fortified with 25% of the DV for zinc, ¾ cup serving3.825
Lobster, cooked, 3 ounces3.423
Pork chop, loin, cooked, 3 ounces2.919
Baked beans, canned, plain or vegetarian, ½ cup2.919
Chicken, dark meat, cooked, 3 ounces2.416
Yogurt, fruit, low fat, 8 ounces1.711
Cashews, dry roasted, 1 ounce1.611
Chickpeas, cooked, ½ cup1.39
Cheese, Swiss, 1 ounce1.28
Oatmeal, instant, plain, prepared with water, 1 packet1.17
Milk, low-fat or non fat, 1 cup1.07
Almonds, dry roasted, 1 ounce0.96
Kidney beans, cooked, ½ cup0.96
Chicken breast, roasted, skin removed, ½ breast0.96
Cheese, cheddar or mozzarella, 1 ounce0.96
Peas, green, frozen, cooked, ½ cup0.53
Flounder or sole, cooked, 3 ounces0.32

Footnote: * DV = Daily Value. DVs were developed by the U.S. Food and Drug Administration to help consumers compare the nutrient contents of products within the context of a total diet. The DV for zinc is 15 mg for adults and children age 4 and older. Food labels, however, are not required to list zinc content unless a food has been fortified with this nutrient. Foods providing 20% or more of the DV are considered to be high sources of a nutrient.

[Source 129)]

Most Americans get enough zinc from the foods they eat.

However, certain groups of people are more likely than others to have trouble getting enough zinc:

  • People who have had gastrointestinal surgery, such as weight loss surgery, or who have digestive disorders, such as ulcerative colitis or Crohn’s disease. These conditions can both decrease the amount of zinc that the body absorbs and increase the amount lost in the urine.
  • Vegetarians because they do not eat meat, which is a good source of zinc. Also, the beans and grains they typically eat have compounds that keep zinc from being fully absorbed by the body. For this reason, vegetarians might need to eat as much as 50% more zinc than the recommended amounts.
  • Older infants who are breastfed because breast milk does not have enough zinc for infants over 6 months of age. Older infants who do not take formula should be given foods that have zinc such as pureed meats. Formula-fed infants get enough zinc from infant formula.
  • Alcoholics because alcoholic beverages decrease the amount of zinc that the body absorbs and increase the amount lost in the urine. Also, many alcoholics eat a limited amount and variety of food, so they may not get enough zinc.
  • People with sickle cell disease because they might need more zinc.

Zinc and healthy eating

People should get most of their nutrients from food because 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.

Groups at Risk of Zinc Inadequacy

In North America, overt zinc deficiency is uncommon 130). When zinc deficiency does occur, it is usually due to inadequate zinc intake or absorption, increased losses of zinc from the body, or increased requirements for zinc 131), 132), 133). People at risk of zinc deficiency or inadequacy need to include good sources of zinc in their daily diets. Supplemental zinc might also be appropriate in certain situations.

  • People with gastrointestinal and other diseases

Gastrointestinal surgery and digestive disorders (such as ulcerative colitis, Crohn’s disease, and short bowel syndrome) can decrease zinc absorption and increase endogenous zinc losses primarily from the gastrointestinal tract and, to a lesser extent, from the kidney 134), 135), 136), 137). Other diseases associated with zinc deficiency include malabsorption syndrome, chronic liver disease, chronic renal disease, sickle cell disease, diabetes, malignancy, and other chronic illnesses 138). Chronic diarrhea also leads to excessive loss of zinc 139).

  • Vegetarians

The bioavailability of zinc from vegetarian diets is lower than from non-vegetarian diets because vegetarians do not eat meat, which is high in bioavailable zinc and may enhance zinc absorption. In addition, vegetarians typically eat high levels of legumes and whole grains, which contain phytates that bind zinc and inhibit its absorption 140), 141).

Vegetarians sometimes require as much as 50% more of the RDA for zinc than non-vegetarians 142). In addition, they might benefit from using certain food preparation techniques that reduce the binding of zinc by phytates and increase its bioavailability. Techniques to increase zinc bioavailability include soaking beans, grains, and seeds in water for several hours before cooking them and allowing them to sit after soaking until sprouts form 143). Vegetarians can also increase their zinc intake by consuming more leavened grain products (such as bread) than unleavened products (such as crackers) because leavening partially breaks down the phytate; thus, the body absorbs more zinc from leavened grains than unleavened grains.

  • Pregnant and lactating women

Pregnant women, particularly those starting their pregnancy with marginal zinc status, are at increased risk of becoming zinc insufficient due, in part, to high fetal requirements for zinc 144). Lactation can also deplete maternal zinc stores 145). For these reasons, the RDA for zinc is higher for pregnant and lactating women than for other women (see Table 1) 146).

  • Older infants who are exclusively breastfed

Breast milk provides sufficient zinc (2 mg/day) for the first 4–6 months of life but does not provide recommended amounts of zinc for infants aged 7–12 months, who need 3 mg/day147), 148). In addition to breast milk, infants aged 7–12 months should consume age-appropriate foods or formula containing zinc 149). Zinc supplementation has improved the growth rate in some children who demonstrate mild-to-moderate growth failure and who have a zinc deficiency 150), 151).

  • People with sickle cell disease

Results from a large cross-sectional survey suggest that 44% of children with sickle cell disease have a low plasma zinc concentration 152), possibly due to increased nutrient requirements and/or poor nutritional status 153). Zinc deficiency also affects approximately 60%–70% of adults with sickle cell disease 154). Zinc supplementation has been shown to improve growth in children with sickle cell disease 155).

  • Alcoholics

Approximately 30%–50% of alcoholics have low zinc status because ethanol consumption decreases intestinal absorption of zinc and increases urinary zinc excretion 156). In addition, the variety and amount of food consumed by many alcoholics is limited, leading to inadequate zinc intake 157), 158), 159).

What happens if you don’t get enough zinc?

Zinc deficiency is rare in North America. It causes slow growth in infants and children, delayed sexual development in adolescents and impotence in men. Zinc deficiency also causes hair loss, diarrhea, eye and skin sores and loss of appetite. Weight loss, problems with wound healing, decreased ability to taste food, and lower alertness levels can also occur.

Many of these symptoms can be signs of problems other than zinc deficiency. If you have these symptoms, your doctor can help determine whether you might have a zinc deficiency.

Zinc Deficiency

Dietary deficiency is unlikely in healthy persons. Secondary zinc deficiency can develop in the following 160):

  • Patients taking diuretics
  • Patients with diabetes mellitus, sickle cell disease, chronic kidney disease, liver disease, chronic alcoholism, or malabsorption
  • Patients with stressful conditions (eg, sepsis, burns, head injury)
  • Older adults (65 years and older)
  • Elderly institutionalized and homebound patients (common).
  • Premature and low-birth-weight infants
  • Older breast-fed infants and toddlers with inadequate intake of zinc-rich complementary foods
  • Children and adolescents
  • Pregnant and lactating (breast-feeding) women, especially adolescents
  • Patients receiving total parenteral nutrition (intravenous feedings)
  • Malnourished individuals, including those with protein-energy malnutrition and anorexia nervosa
  • Individuals with severe or persistent diarrhea
  • Individuals with malabsorption syndromes, including celiac disease and short bowel syndrome
  • Individuals with inflammatory bowel disease, including Crohn’s disease and ulcerative colitis
  • Alcoholics and those with alcoholic liver disease who have increased urinary zinc excretion and low liver zinc levels
  • Individuals with chronic renal disease
  • Individuals with sickle cell anemia
  • Individuals who use medications that decrease intestinal zinc absorption, increase zinc excretion, or impair zinc utilization (see Drug interactions)
  • Vegetarians: The requirement for dietary zinc may be as much as 50% greater for vegetarians whose major food staples are grains and legumes, because high levels of phytate in these foods reduce zinc absorption 161).

Maternal zinc deficiency may cause fetal malformations and low birth weight 162).

Zinc deficiency in children causes impaired growth, impaired taste (hypogeusia), delayed sexual maturation, and hypogonadism. In children or adults, manifestations also include alopecia, impaired immunity, anorexia, dermatitis, night blindness, anemia, lethargy, and impaired wound healing 163).

Zinc deficiency should be suspected in undernourished patients with typical symptoms or signs. However, because many of the symptoms and signs are nonspecific, clinical diagnosis of mild zinc deficiency is difficult. Laboratory diagnosis is also difficult. Low albumin levels, common in zinc deficiency, make serum zinc levels difficult to interpret; diagnosis usually requires the combination of low levels of zinc in serum and increased urinary zinc excretion. If available, isotope studies can measure zinc status more accurately.

Zinc deficiency is characterized by growth retardation, loss of appetite, and impaired immune function. In more severe cases, zinc deficiency causes hair loss, diarrhea, delayed sexual maturation, impotence, hypogonadism in males, and eye and skin lesions 164), 165), 166), 167). Weight loss, delayed healing of wounds, taste abnormalities, and mental lethargy can also occur 168), 169), 170), 171), 172), 173), 174). Many of these symptoms are non-specific and often associated with other health conditions; therefore, a medical examination is necessary to ascertain whether a zinc deficiency is present.

Zinc nutritional status is difficult to measure adequately using laboratory tests 175), 176), 177) due to its distribution throughout the body as a component of various proteins and nucleic acids 178). Plasma or serum zinc levels are the most commonly used indices for evaluating zinc deficiency, but these levels do not necessarily reflect cellular zinc status due to tight homeostatic control mechanisms 179). Clinical effects of zinc deficiency can be present in the absence of abnormal laboratory indices [8]. Clinicians consider risk factors (such as inadequate caloric intake, alcoholism, and digestive diseases) and symptoms of zinc deficiency (such as impaired growth in infants and children) when determining the need for zinc supplementation 180).

Treatment of zinc deficiency consists of elemental zinc 15 to 120 mg po once/day until symptoms and signs resolve 181).

Inherited zinc deficiency

Much of what is known about severe zinc deficiency was derived from the study of individuals born with acrodermatitis enteropathica, a genetic disorder resulting from the impaired uptake and transport of zinc 182). The symptoms of severe zinc deficiency include the slowing or cessation of growth and development, delayed sexual maturation, characteristic skin rashes, chronic and severe diarrhea, immune system deficiencies, impaired wound healing, diminished appetite, impaired taste sensation, night blindness, swelling and clouding of the cornea, and behavioral disturbances. Before the cause of acrodermatitis enteropathica was known, patients typically died in infancy. Oral zinc therapy results in the complete remission of symptoms, though it must be maintained indefinitely in individuals with the genetic disorder 183).

Acquired zinc deficiency

It is now recognized that milder zinc deficiency contributes to a number of health problems, especially common in children who live in low-resource countries. An estimated 2 billion people worldwide are affected by dietary zinc deficiency 184). The lack of a sensitive and specific indicator of marginal zinc deficiency hinders the scientific study of its health implications 185). However, controlled trials of moderate zinc supplementation have demonstrated that marginal zinc deficiency contributes to impaired physical and neuropsychological development and increased susceptibility to life-threatening infections in young children 186). In fact, zinc deficiency has been estimated to cause more than 450,000 deaths annually in children under five years of age, comprising 4.4% of global childhood deaths 187).

In industrialized countries, dietary zinc deficiency is unlikely to cause severe zinc deficiency in individuals without a genetic disorder, zinc malabsorption or conditions of increased zinc loss, such as severe burns or prolonged diarrhea. Severe zinc deficiency has also been reported in individuals undergoing total parenteral nutrition without zinc, in those who abuse alcohol, and in those who are taking certain medications like penicillamine 188).

Diseases or conditions related to zinc deficiency

Pregnancy complications and adverse pregnancy outcomes

Estimates based on national food supply indicate that dietary zinc intake is likely inadequate in most low- and middle-income countries, especially those in Sub-Saharan Africa and South Asia 189). Inadequate zinc status during pregnancy interferes with fetal development, and preterm neonates from zinc-deficient mothers suffer from growth retardation and dermatitis and are at risk of infections, necrotizing enterocolitis, chronic lung disease, and retinopathy of prematurity 190). Maternal zinc deficiency has also been associated with a number of pregnancy complications and poor outcomes. A recent case-control study conducted in an Iranian hospital reported higher odds of congenital malformations in newborns of mothers with low serum zinc concentrations during the last month of pregnancy 191). A 2016 review of 64 observational studies 192) found an inverse relationship between maternal zinc status and the severity of preeclampsia, as well as between maternal zinc intake and the risk of low-birth-weight newborns. There were no apparent associations between maternal zinc status and the risk of gestational diabetes mellitus and preterm birth. However, the conclusions of this analysis were limited by the fact that most observational studies were conducted in women from populations not at risk for zinc deficiency 193).

To date, available evidence from maternal zinc intervention trials conducted worldwide does not support the recommendation of routine zinc supplementation during pregnancy. A 2015 systematic review and meta-analysis of 21 randomized controlled trials in over 17,000 women and their babies found a 14% reduction in premature deliveries with zinc supplementation during pregnancy, mainly in low-income women 194). This analysis, however, did not find zinc supplementation to benefit other indicators of maternal or infant health, including stillbirth or neonatal death, low birth weight, small-for-gestational age, and pregnancy-induced hypertension. There was also no effect of supplemental zinc on postpartum hemorrhage, maternal infections, congenital malformations, and child development outcomes 195). A recent review of 17 trials (of which 15 were conducted in low- and middle-income countries) found that maternal supplementation with multiple micronutrients (including, among others, zinc, iron, and folic acid) reduced the risk of low-birth-weight newborns and small-for-gestational age infants when compared to supplemental iron with or without folic acid 196). While multiple micronutrient supplementation would likely benefit pregnant women with coexisting micronutrient deficiencies in low- and middle-income countries, there is no evidence to recommend zinc supplementation in isolation in pregnant women from any settings 197).

Impaired growth, growth retardation and development

Significant delays in linear growth and weight gain, known as growth retardation or failure to thrive, are common features of mild zinc deficiency in children. In the 1970s and 1980s, several randomized, placebo-controlled studies of zinc supplementation in young children with significant growth delays were conducted in Denver, Colorado. Modest zinc supplementation (5.7 mg/day) resulted in increased growth rates compared to placebo 198). Several meta-analyses of growth data from zinc intervention trials have confirmed the widespread occurrence of growth-limiting zinc deficiency in young children, especially in low- and middle-income countries 199). A 2018 systematic review and meta-analysis identified 54 trials 200) that examined the impact of zinc supplementation during infancy (on average, 7.6 mg/day for 30.9 weeks) or childhood (on average, 8.5 mg/day for 38.9 weeks) on child anthropometric measurements. There was evidence of a positive effect of supplemental zinc on children’s height, weight, and weight-for-age Z score (WAZ), but neither on height-for-age Z score (HAZ) or weight-for-height Z score (WHZ). In addition, zinc supplementation did not reduce the risks of underweight (WAZ<-2 standard deviation [SD]), wasting (WHZ<-2 SD), or stunting (HAZ<-2 SD) in children 201). Although the exact mechanisms for the growth-limiting effect of zinc deficiency are not known, research indicates that zinc availability affects cell-signaling systems that coordinate the response to the growth-regulating hormone, insulin-like growth factor-1 (IGF-1) 202).

Delayed mental and psychomotor development in young children

Adequate nutrition in essential for brain growth and development, especially during the first 1,000 days of life — a critical period of development for all organs and systems spanning from conception to 24 months of age 203). Animal studies 204) have established that zinc deficiency in early life interferes with normal brain development and cognitive functions. Data on the effect of zinc supplementation during pregnancy on infants’ neurologic and psychomotor outcomes is very limited. In a randomized, placebo-controlled trial in African-American women, daily maternal supplementation with 25 mg of zinc from about 19 weeks’ gestation had no effect on neurologic development test scores in their children at five years of age 205).

Several studies have reported on the effect of postnatal zinc supplementation on mental and motor development. Two early randomized controlled trials, one conducted in India and the other in Guatemala, suggested that postnatal supplementation with 10 mg/day of zinc resulted in toddlers being more vigorous 206) and functionally active 207). In one trial conducted in Brazilian newborns from low-income families and weighing between 1,500 g and 2,499 g at birth 208), neither zinc supplementation for eight weeks with 1 mg/day or 5 mg/day improved mental and psychomotor development at 6 or 12 months of age compared to a placebo and assessed using the Bayley Scales of Infant Development (BSID) for Mental Development Index (MDI) and Psychomotor Development Index (PDI). Additionally, a randomized, placebo-controlled, double-blind trial in Chilean newborns (birth weights >2,300 g) from low-income families reported no effect of zinc supplementation (5 mg/day) on mental and psychomotor development indices at 6 and 12 months 209). Two other trials found that supplemental zinc failed to improve MDI or PDI at 12 months of age when zinc (10 mg/day) was given to six-month-old infants for six months 210) or at the end of the intervention in toddlers aged 12-18 months when zinc (30 mg/day) was given for four months 211). A 2012 Cochrane review of eight clinical trials found no evidence that postnatal zinc supplementation improves mental or motor development of infants and children from populations with presumably inadequate zinc status 212).

Impaired immune system function

Adequate zinc intake is essential in maintaining the integrity of the immune system 213), specifically for normal development and function of cells that mediate both innate (neutrophils, macrophages, and natural killer cells) and adaptive (B-lymphocytes and T-lymphocytes) immune responses 214). Because pathogens also require zinc to thrive and invade, a well-established antimicrobial defense mechanism in the body sequesters free zinc away from microbes 215). Another opposite mechanism consists in intoxicating intracellular microbes within macrophages with excess zinc 216). Through weakening innate and adaptive immune responses, zinc deficiency diminishes the capacity of the body to combat pathogens 217). As a consequence, zinc-deficient individuals experience an increased susceptibility to a variety of infectious agents 218).

Increased susceptibility to infectious disease in children

Diarrhea

Zinc promotes mucosal resistance to infections by supporting the activity of immune cells and the production of antibodies against invading pathogens 219). Therefore, a deficiency in zinc increases the susceptibility to intestinal infections and constitutes a major contributor to diarrheal diseases in children 220). In turn, persistent diarrhea contributes to zinc deficiency and malnutrition 221). Research indicates that zinc deficiency may also potentiate the effects of toxins produced by diarrhea-causing bacteria like E. coli 222). It is estimated that diarrheal diseases are responsible for the deaths of about 500,000 children under five years of age annually in low- and middle-income countries 223). Zinc supplementation in combination with oral rehydration therapy has been shown to significantly reduce the duration and severity of acute and persistent childhood diarrhea and to increase survival in a number of randomized controlled trials 224). A 2016 meta-analysis of randomized controlled trials found that zinc supplementation reduced the duration of acute diarrhea by one day in children aged >6 months who presented signs of malnutrition (5 trials; 419 children) 225). However, there was little evidence to suggest that zinc could be as efficacious to reduce the duration of acute diarrheal episodes in children aged <6 months and in well-nourished children aged >6 months. Zinc supplementation also reduced the duration of persistent diarrhea in children by more than half a day (5 trials; 529 children) 226).

The World Health Organization (WHO) and the United Nations Children’s Fund (UNICEF) currently recommend supplementing young children with 10 to 20 mg/day of zinc as part of the treatment for acute diarrheal episodes and to prevent further episodes in the two to three months following zinc supplementation 227).

Pneumonia

Pneumonia — caused by lower respiratory tract viral or bacterial infections (LRTIs) — accounts for nearly 1 million deaths among children annually, primarily in low-and middle-income countries 228). Vaccinations against Haemophilus influenzae type B, pneumococcus, pertussis (whooping cough), and measles can help prevent pneumonia 229). According to a 2009 WHO report on disease risk factors, zinc deficiency may be responsible for 13% of all LRTI cases, primarily pneumonia and flu cases, in children younger than 5 years 230). Accordingly, a 2016 meta-analysis of six trials found that zinc supplementation in children under 5 years old reduced the risk of pneumonia by 13% 231). However, it remains unclear whether supplemental zinc, in conjunction with antibiotic therapy, is beneficial in the treatment of pneumonia. A recent randomized, placebo-controlled trial conducted in Gambian children who were not zinc deficient failed to show any benefit of zinc supplementation (10 mg/day or 20 mg/day [depending on child’s age] for 7 days) given alongside antibiotics in the treatment of severe pneumonia 232). A 2018 meta-analysis of five trials (1,822 participants) found no improvement when zinc was used as an adjunct to antibiotic treatment in children with pneumonia 233). There was, however, evidence that supplemental zinc reduced the risk of pneumonia-related mortality (3 trials; 1,318 participants) 234).

Malaria

Early studies have indicated that zinc supplementation may reduce the incidence of clinical attacks of malaria in children 235). A placebo-controlled trial in preschool-aged children in Papua New Guinea found that zinc supplementation reduced the frequency of health center attendance due to Plasmodium falciparum malaria by 38% 236). Additionally, the number of malaria episodes accompanied by high circulating parasite concentrations was reduced by 68%, suggesting that zinc supplementation may be of benefit in preventing more severe episodes of malaria. However, a six-month trial in more than 700 West African children did not find any difference in the frequency or severity of malaria episodes between children supplemented with zinc and those given a placebo 237). Another randomized controlled trial reported that zinc supplementation did not benefit preschool-aged children with acute, uncomplicated malaria 238). There is also little evidence to suggest that zinc supplementation could reduce the risk of malaria-related mortality in children 239). At present, there is not enough evidence to suggest a prophylactic and/or therapeutic role for supplemental zinc in the management of childhood malaria 240). A recent randomized, placebo-controlled trial did not provide clear-cut evidence of a protective effect of zinc (25 mg/day) administered to Tanzanian women during their first gestational trimester until delivery on the risk of placental malaria infection 241).

Age-related decline in immune function

Inadequate zinc status in elderly subjects is not uncommon and is thought to exacerbate the age-related decline in immune function 242). In one study, low serum zinc concentrations in nursing home residents were associated with higher risks of pneumonia and pneumonia-related and all-cause mortality 243). Trials examining the effects of zinc supplementation on immune function in middle-aged and elderly adults have given mixed results 244). Some studies showed mixed or no effects of zinc supplementation on parameters of immune function 245). However, zinc supplementation was found to have a positive impact on certain aspects of immune function that are affected by zinc deficiency, such as the decline in T-cell (a type of lymphocyte) function 246). For example, a randomized, placebo-controlled study in adults over 65 years of age found that zinc supplementation (25 mg/day) for three months increased blood concentrations of helper T-cells and cytotoxic T-cells 247). Additionally, a randomized, double-blind, placebo-controlled trial in 101 older adults (aged 50-70 years) with normal blood zinc concentrations showed that zinc supplementation at 15 mg/day for six months improved the helper T-cells/cytotoxic T-cells ratio, which tends to decline with age and is a predictor of survival 248). However, the study also suggested that a dose of 30 mg/day of zinc might reduce the number of B-lymphocytes, which play a central role in humoral immunity. Further, zinc supplementation had no effect on various immune parameters, including markers of inflammation, measures of granulocyte and monocyte phagocytic capacity, or cytokine production by activated monocytes 249).

A more recent trial examined the effect of daily supplementation with a multiple micronutrients, including 5 mg or 30 mg of zinc for three months, on zinc status and markers of immune function in institutionalized elderly participants (mean age, >80 years) with low serum zinc concentrations 250). Zinc status was improved with the 30 mg/day dose — but not with 5 mg/day — yet the most zinc-deficient individuals failed to achieve normal serum zinc concentrations within the intervention period. The number of circulating T-cells was also significantly increased in those who took the micronutrient supplement with the higher versus low dose of zinc 251).

More research is warranted before zinc supplementation could be recommended to older adults, especially those with no symptoms of declining immunity. Nonetheless, the high prevalence of zinc deficiency among institutionalized elderly adults should be addressed and would likely improve the performance of their immune systems 252).

Type 2 diabetes mellitus

There is a close relationship between zinc and insulin action. Specifically, in pancreatic beta-cells, zinc is involved in insulin synthesis and storage in secretory vesicles. Zinc is released with the hormone when blood glucose concentrations increase 253). Zinc is also understood to stimulate glucose uptake and metabolism by insulin-sensitive tissues through triggering the intracellular insulin signaling pathway 254). Single-nucleotide polymorphisms (SNPs) in the SLC30A8 (solute carrier family 30 member 8) gene, coding for a zinc transporter that co-localizes with insulin in β-cells, have been associated with higher risks of type 1 and type 2 diabetes mellitus 255), though the risk for type 2 diabetes mellitus was found to be reduced with rare protein-truncating variants of the gene 256). The first prospective cohort study to examine the risk of type 2 diabetes in relation to zinc intakes — the Nurses’ Health Study 257) followed 82,297 US registered female nurses for 24 years. The data analysis showed an 8% lower risk of type 2 diabetes with the highest versus lowest intake of dietary zinc (median values, 11.8 mg/day versus 4.9 mg/day). This finding was consistent with the result of the Australian Longitudinal Study on Women’s Health (ALSWH) that enrolled 8,921 women for six years and showed a 50% lower risk of diabetes with the highest versus lowest intake of energy-adjusted dietary zinc 258). Both Nurses’ Health Study and ALSWH studies also reported a reduced risk of diabetes with higher versus lower zinc-to-heme iron ratios in the diet, although the significance is unclear as nonheme iron, rather than heme iron, is known to interfere with dietary zinc absorption. Heme iron may be an indicator of red meat consumption, which has been positively associated with the risk of type 2 diabetes 259). However, two other prospective cohort studies — the Multi-Ethnic Study of Atherosclerosis (MESA; 4,982 participants) and the National Institutes of Health-American Association of Retired Persons (NIH-AARP) Diet and Health Study (232,007 participants) — failed to find evidence for an association between zinc intake and risk of type 2 diabetes 260). Another recent prospective cohort study, the Malmo Diet and Cancer Study in 26,132 middle-aged Swedish participants followed for 19 years, found an increased risk of diabetes with higher dietary zinc intakes yet a lower risk of diabetes in zinc supplement users (versus non-users) and in those with a higher zinc-to-iron intake ratio 261). The authors reported a stronger inverse association between zinc-to-iron intake ratio and risk of diabetes among obese participants carrying a specific SLC30A8 genotype 262).

The results of a few short-term intervention studies suggest that zinc supplementation may improve glucose handling in subjects with prediabetes. A 2015 systematic review 263) identified three short trials (4 to 12 weeks) conducted in adults with prediabetes and found little evidence of an improvement in insulin resistance with zinc supplementation. However, a 2016 randomized, placebo-controlled trial 264) in 55 Bangladeshi with prediabetes showed that daily supplementation with zinc sulfate (30 mg/day for 6 months) improved fasting blood glucose, as well as measures of β-cell function and insulin sensitivity. Similar observations were made in another recent trial in 100 Sri Lankan randomized to receive daily supplementation with zinc (20 mg of elemental zinc) or a placebo for one year 265). Supplemental zinc improved zinc status and measures of glycemic control 266). Large-scale, long-term studies are necessary to provide definite conclusions regarding the potential benefit of zinc supplementation in subjects at risk of type 2 diabetes.

Can too much zinc be harmful?

Yes, if you get too much. Signs of too much zinc include nausea, vomiting, loss of appetite, stomach cramps, diarrhea, and headaches. When people take too much zinc for a long time, they sometimes have problems such as low copper levels, lower immunity, and low levels of HDL cholesterol (the “good” cholesterol). One case report cited severe nausea and vomiting within 30 minutes of ingesting 4 g of zinc gluconate (570 mg elemental zinc) 267). Intakes of 150–450 mg of zinc per day have been associated with such chronic effects as low copper status, altered iron function, reduced immune function, and reduced levels of high-density lipoproteins 268). Reductions in a copper-containing enzyme, a marker of copper status, have been reported with even moderately high zinc intakes of approximately 60 mg/day for up to 10 weeks 269). The doses of zinc used in the AREDS study (80 mg per day of zinc in the form of zinc oxide for 6.3 years, on average) have been associated with a significant increase in hospitalizations for genitourinary causes, raising the possibility that chronically high intakes of zinc adversely affect some aspects of urinary physiology 270).

Zinc and copper interactions

Taking large quantities of zinc (50 mg/day or more) over a period of weeks can interfere with copper bioavailability. High intake of zinc induces the intestinal synthesis of a copper-binding protein called metallothionein. Metallothionein traps copper within intestinal cells and prevents its systemic absorption (see Wilson’s disease). More typical intakes of zinc do not affect copper absorption, and high copper intakes do not affect zinc absorption 271).

Zinc and iron interactions

Iron and zinc compete for absorptive pathways 272). Supplemental (38-65 mg/day of elemental iron) but not dietary levels of iron may decrease zinc absorption 273). This interaction is of concern in the management of iron supplementation during pregnancy and lactation and has led some experts to recommend zinc supplementation for pregnant and lactating women taking iron supplements 274). Food fortification with iron has not been shown to negatively affect zinc absorption 275). In a placebo-controlled study, supplementation with zinc (10 mg/day) for three months in children aged eight to nine years significantly decreased serum iron concentrations, yet not to the extent of causing anemia 276). Additional randomized controlled studies have reported a worsening of nutritional iron status with chronic zinc supplementation 277).

Zinc and calcium interactions

High levels of dietary calcium impair zinc absorption in animals, but it is uncertain whether this occur in humans 278). One study showed that increasing the calcium intake of postmenopausal women by 890 mg/day in the form of milk or calcium phosphate (total calcium intake, 1,360 mg/day) reduced zinc absorption and zinc balance in postmenopausal women 279). However, another study found that increasing the calcium intake of adolescent girls by 1,000 mg/day in the form of calcium citrate malate (total calcium intake, 1,667 mg/day) did not affect zinc absorption or balance 280). Calcium in combination with phytate might affect zinc absorption, which would be particularly relevant to individuals who very frequently consume tortillas made with lime (i.e., calcium oxide). A study in 10 healthy women (age range, 21-47 years) found that high intake of dietary calcium (~1,800 mg/day) did not impair zinc absorption regardless of the phytate content of the diet 281).

Zinc and folate interactions

The bioavailability of dietary folate (vitamin B9) is increased by the action of a zinc-dependent enzyme. Accordingly, some studies found low zinc intake decreased folate absorption. It was also suggested that supplementation with folic acid — the synthetic form of folate — might impair zinc utilization in individuals with marginal zinc status 282). However, one study reported that supplementation with a relatively high dose of folic acid (800 µg/day) for 25 days did not alter zinc absorption or status in a group of students being fed a low-zinc diet (3.5 mg/day) 283).

Zinc and vitamin A interactions

Zinc and vitamin A interact in several ways. Zinc is a component of retinol-binding protein, a protein necessary for transporting vitamin A in the blood. Zinc is also required for the enzyme that converts retinol (vitamin A) to retinal. This latter form of vitamin A is necessary for the synthesis of rhodopsin, a protein in the eye that absorbs light and thus is involved in dark adaptation. Zinc deficiency has been associated with a decreased release of vitamin A from the liver, which may contribute to symptoms of night blindness that are seen with zinc deficiency 284).

Zinc Toxicity

The recommended upper limit in adults for zinc intake is 40 mg/day; the upper limit is lower for younger people. Toxicity is rare 285).

Ingesting doses of elemental zinc ranging from 100 to 150 mg/day for prolonged periods interferes with copper metabolism and causes low blood copper levels, red blood cell microcytosis, neutropenia, and impaired immunity; higher doses should be given only for short periods of time and the patient followed closely.

Ingesting larger amounts (200 to 800 mg/day), usually by consuming acidic food or drinking from a galvanized (zinc-coated) container, can cause anorexia, vomiting, and diarrhea. Chronic toxicity may result in copper deficiency and may cause nerve damage.

Metal fume fever, also called brass-founders’ ague or zinc shakes, is caused by inhaling industrial zinc oxide fumes; it results in fever, dyspnea, nausea, fatigue, and myalgias. Symptom onset is usually 4 to 12 h after exposure. Symptoms usually resolve after 12 to 24 h in a zinc-free environment.

Diagnosis of zinc toxicity is usually based on the time course and a history of exposure.

Treatment of zinc toxicity consists of eliminating exposure to zinc; no antidotes are available.

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