- What is Zinc
- What Does Zinc Do
- Zinc supplements
- Other Sources of Zinc
- Benefits of Zinc on Health
- How much zinc do you need ?
- What foods provide zinc ?
- What happens if you don’t get enough zinc ?
- Can too much zinc be harmful ?
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.
Zinc is found in cells throughout the body, found mainly in bones, teeth, hair, skin, liver, muscle, leukocytes, and testes 1). 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.
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 2), 3) and it plays a role in immune function 4), 5), protein synthesis 6), wound healing 7), DNA synthesis 8), 9) and cell division 10). Zinc also supports normal growth and development during pregnancy, childhood, and adolescence 11), 12), 13) and is required for proper sense of taste and smell 14). A daily intake of zinc is required to maintain a steady state because the body has no specialized zinc storage system 15).
Supplements contain several forms of zinc, including zinc gluconate, zinc sulfate, and zinc acetate 16). 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 17).
In addition to standard tablets and capsules, some zinc-containing cold lozenges are labeled as dietary supplements.
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 18). Taking iron supplements between meals helps decrease its effect on zinc absorption 19).
High zinc intakes can inhibit copper absorption, sometimes producing copper deficiency and associated anemia 20), 21). 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 22), 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 23), 24). In June 2009, the FDA warned consumers to stop using three zinc-containing intranasal products because they might cause anosmia 25). 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 26). 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 27), 28). Many denture creams have now been reformulated to eliminate zinc.
Benefits of Zinc on Health
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 29), 30). 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 31). 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 32), 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 33). 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 34). 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 35) but had no effect in the other 36).
A Cochrane review concluded that the evidence supporting the use of antioxidant vitamins and zinc for AMD comes primarily from the AREDS study 37). Individuals who have or are developing AMD should talk to their health care provider about taking a zinc-containing AREDS supplement.
The 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 38). There is no proven treatment for the common cold 39). 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 40). 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 41).
There’s been a lot of talk about taking zinc for colds ever since a 1984 study 42) 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 43), 44), 45) and a positive result for zinc in the treatment for common colds 46), 47), 48), 49).
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) 50).
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 51). 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 52).
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 53).
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 54). 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 55), 56), 57).
Recently analyses of several studies 58), 59), 60) 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 61) 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 62). 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 63). 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 64). 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 65). 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 66).
In the USA, the recommended dietary zinc intake is 11 mg/day for men and 8 mg/day for women 67). 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 68). 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 69), 70), 71), 72). 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 73).
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 74). Zinc deficiency causes alterations in immune response that probably contribute to increased susceptibility to infections, such as those that cause diarrhea, especially in children 75).
Studies show that poor, malnourished children in India, Africa, South America, and Southeast Asia experience shorter courses of infectious diarrhea after taking zinc supplements 76). The children in these studies received 4–40 mg of zinc a day in the form of zinc acetate, zinc gluconate, or zinc sulfate 77).
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 78). Similar findings were reported in a meta-analysis published in 2008 and a 2007 review of zinc supplementation for preventing and treating diarrhea 79), 80). 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 81).
In a 2016 Cochrane Review 82) 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 83). 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 84).
Zinc helps maintain the integrity of skin and mucosal membranes 85). Patients with chronic leg ulcers have abnormal zinc metabolism and low serum zinc levels , and clinicians frequently treat skin ulcers with zinc supplements 86). 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 87), 88). 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 89).
Severe zinc deficiency depresses immune function 90), and even mild to moderate degrees of zinc deficiency can impair macrophage and neutrophil functions, natural killer cell activity, and complement activity 91). The body requires zinc to develop and activate T-lymphocytes 92), 93). 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 94), 95). 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 96), 97), 98), 99).
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 100). 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 101), 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 102).
The current RDAs for zinc are listed in Table 1 103). 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 Stage||Recommended Amount|
|Birth to 6 months||2 mg|
|Infants 7–12 months||3 mg|
|Children 1–3 years||3 mg|
|Children 4–8 years||5 mg|
|Children 9–13 years||8 mg|
|Teens 14–18 years (boys)||11 mg|
|Teens 14–18 years (girls)||9 mg|
|Adults (men)||11 mg|
|Adults (women)||8 mg|
|Pregnant teens||12 mg|
|Pregnant women||11 mg|
|Breastfeeding teens||13 mg|
|Breastfeeding women||12 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 104) and the 1994 Continuing Survey of Food Intakes of Individuals 105).
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 106).
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) 107). 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 108).
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 109), 110), 111). 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 112).
The U.S. Department of Agriculture’s (USDA’s) Nutrient Database website 113) lists the nutrient content of many foods and provides a comprehensive list of foods containing zinc arranged by nutrient content 114) and by food name 115).
Table 2: Selected Food Sources of Zinc
|Oysters, cooked, breaded and fried, 3 ounces||74.0||493|
|Beef chuck roast, braised, 3 ounces||7.0||47|
|Crab, Alaska king, cooked, 3 ounces||6.5||43|
|Beef patty, broiled, 3 ounces||5.3||35|
|Breakfast cereal, fortified with 25% of the DV for zinc, ¾ cup serving||3.8||25|
|Lobster, cooked, 3 ounces||3.4||23|
|Pork chop, loin, cooked, 3 ounces||2.9||19|
|Baked beans, canned, plain or vegetarian, ½ cup||2.9||19|
|Chicken, dark meat, cooked, 3 ounces||2.4||16|
|Yogurt, fruit, low fat, 8 ounces||1.7||11|
|Cashews, dry roasted, 1 ounce||1.6||11|
|Chickpeas, cooked, ½ cup||1.3||9|
|Cheese, Swiss, 1 ounce||1.2||8|
|Oatmeal, instant, plain, prepared with water, 1 packet||1.1||7|
|Milk, low-fat or non fat, 1 cup||1.0||7|
|Almonds, dry roasted, 1 ounce||0.9||6|
|Kidney beans, cooked, ½ cup||0.9||6|
|Chicken breast, roasted, skin removed, ½ breast||0.9||6|
|Cheese, cheddar or mozzarella, 1 ounce||0.9||6|
|Peas, green, frozen, cooked, ½ cup||0.5||3|
|Flounder or sole, cooked, 3 ounces||0.3||2|
* 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 116)]
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 117). 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 118), 119), 120). 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 121), 122), 123), 124). Other diseases associated with zinc deficiency include malabsorption syndrome, chronic liver disease, chronic renal disease, sickle cell disease, diabetes, malignancy, and other chronic illnesses 125). Chronic diarrhea also leads to excessive loss of zinc 126).
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 127), 128).
Vegetarians sometimes require as much as 50% more of the RDA for zinc than non-vegetarians 129). 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 130). 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 131). Lactation can also deplete maternal zinc stores 132). For these reasons, the RDA for zinc is higher for pregnant and lactating women than for other women (see Table 1) 133).
- 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/day134), 135). In addition to breast milk, infants aged 7–12 months should consume age-appropriate foods or formula containing zinc 136). Zinc supplementation has improved the growth rate in some children who demonstrate mild-to-moderate growth failure and who have a zinc deficiency 137), 138).
- 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 139), possibly due to increased nutrient requirements and/or poor nutritional status 140). Zinc deficiency also affects approximately 60%–70% of adults with sickle cell disease 141). Zinc supplementation has been shown to improve growth in children with sickle cell disease 142).
Approximately 30%–50% of alcoholics have low zinc status because ethanol consumption decreases intestinal absorption of zinc and increases urinary zinc excretion 143). In addition, the variety and amount of food consumed by many alcoholics is limited, leading to inadequate zinc intake 144), 145), 146).
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.
Dietary deficiency is unlikely in healthy persons. Secondary zinc deficiency can develop in the following 147):
- 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)
- Elderly institutionalized and homebound patients (common).
Maternal zinc deficiency may cause fetal malformations and low birth weight 148).
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 149).
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 150), 151), 152), 153). Weight loss, delayed healing of wounds, taste abnormalities, and mental lethargy can also occur 154), 155), 156), 157), 158), 159), 160). 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 161), 162), 163) due to its distribution throughout the body as a component of various proteins and nucleic acids 164). 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 165). Clinical effects of zinc deficiency can be present in the absence of abnormal laboratory indices . 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 166).
Treatment of zinc deficiency consists of elemental zinc 15 to 120 mg po once/day until symptoms and signs resolve 167).
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).
The recommended upper limit in adults for zinc intake is 40 mg/day; the upper limit is lower for younger people. Toxicity is rare 168).
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, RBC 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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