Micronutrients: Zinc

Baked beans in a small serving dish
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Determined to be an essential nutrient for humans in 1963, zinc is an antioxidant and trace mineral that we need to consume daily, since our bodies cannot store it. Zinc primarily is involved in supporting the immune system and hundreds of enzymes needed for regulatory and metabolic functions. It also is essential for healthy growth and development from in utero through puberty.

Most Americans consume adequate amounts of zinc. Only 8 percent of people age 2 and older fall short of the estimated average requirement.

Roles in health
Zinc activates lymphocytes, or T-cells, and is crucial in mounting an immune response to resist disease and promote wound healing. Protein and DNA synthesis, cell division, proper taste and smell also rely on zinc.

Zinc lozenges or syrup frequently are used to treat the common cold in adults. If taken within 48 hours of symptoms, zinc may help reduce the duration and severity of symptoms by up to 40 percent. According to a 2011 meta-analysis, daily elemental zinc dosage must be at least 75 milligrams to be effective. However, despite numerous trials, zinc supplementation remains questionable for treating colds. Further, zinc lozenges have been known to cause adverse effects such as a bad mouth taste and constipation, but there is no evidence of long-term harm.

Fertility and low sperm quality in men may be linked to lack of zinc. In one small study, a dietary supplement that included zinc, folate, beta carotene, and vitamins C and E was associated with improved semen quality in men, but it’s not clear if zinc was responsible for these results.

Research suggests zinc and antioxidant vitamins may prevent or slow age-related macular degeneration by preventing cellular retina damage.

Emerging research is evaluating the role of zinc in treating acne, ADHD, osteoporosis and helping to prevent pneumonia.

Current recommendations
Children up to 6 months old have an Adequate Intake of 2 milligrams for both sexes and a Tolerable Upper Intake Level, or UL, of 4 milligrams. For Recommended Dietary Allowances for ages 7 months
and older, see the chart below.

Recommended Dietary Allowances
Age Male Female Pregnancy Lactation UL
7–12 months 3mg 3mg 5mg
1–3 years 3mg 3mg 7mg
4–8 years 5mg 5mg 12mg
9–13 years 8mg 8mg 23mg
14–18 years 11mg 9mg 12mg 13mg 34mg
19+ years 11mg 8mg 11mg 12mg 40mg

Signs of deficiency
Zinc deficiency can impair immune function, wound healing, normal growth and appetite. In a zinc- deficient state, excess oxidation may lead to increased DNA damage.

While most Americans’ zinc intake is adequate, deficiencies could be due to malabsorption, chronic disease, sickle cell disease and poor intake. Excess iron and gastrointestinal conditions can decrease zinc absorption in the body.

In children, zinc deficiency can result in growth retardation and increased risk of infection, diarrhea and respiratory disease. The World Health Organization recommends zinc to help reduce childhood deaths from diarrhea. Deficiency can be difficult to assess because there is not a definitive biomarker of zinc status.

Sources of zinc
In addition to multivitamins, mineral supplements and cold remedies, zinc is found in a variety of foods.

Food sources mg/serving rating
3 ounces cooked oysters (Pacific) 28.3mg Excellent
3 ounces cooked King Alaskan crab 6.5mg Excellent
3 ounces broiled 95% lean beef patty 5.3mg Excellent
3 ounces cooked lean pork loin 2.9mg Excellent
½ cup canned plain or vegetarian baked beans 2.9mg Excellent
1 ounce dry roasted cashews 1.6mg Good

There is not enough evidence to conclude differences in absorption between forms of zinc supplements, including zinc acetate, zinc gluconate, zinc picolinate and zinc sulfate.

Toxicity
Most Americans do not exceed the UL for consumption of zinc with food alone. It is estimated that less than 4 percent of zinc supplement users exceed the UL. Excess zinc can result in toxicity with adverse effects including nausea, vomiting, loss of appetite, stomach cramps, headaches and diarrhea. Long-term overuse (more than 40 milligrams daily) can lead to copper deficiency, which manifests as weakness and numbness in the arms and legs. Persistent use of nasal sprays and gels containing zinc can result in loss of the sense of smell.

Populations at risk
Pregnant women and young children are the highest-risk groups for zinc deficiency. An estimated 17 percent of the global population and 82 percent of pregnant women worldwide have inadequate zinc intakes. Other groups at risk include people with alcoholism, gastrointestinal disorders or chronic renal disease.

Bioavailability of zinc in some plant- based foods may be lower due to phytates that inhibit absorption, requiring up to 50 percent additional zinc for strict vegetarians.

Older adults are likely to consume inadequate amounts of zinc as they contribute to immune dysfunction and chronic inflammation during aging.

It is common for people with diabetes to be moderately zinc-deficient, potentially due to zinc loss through excess urination.

People who are infected with HIV are particularly susceptible to low-serum levels of zinc.

Zinc supplements have the potential to interact with medications and inhibit absorption of both zinc and the medication. Consult a health professional before taking a zinc supplement, especially if you also are taking tetracycline antibiotics, penicillamine or thiazide diuretics.

Bottom line
Zinc is a powerful antioxidant that can help fight infections, repair the body and produce healthy, new cells, but probably not prevent the common cold. A healthy, balanced eating plan can provide an adequate amount of zinc. Vegetarians should be mindful of dietary sources, since some food preparation techniques and food pairings may affect zinc bioavailability or absorption. Older adults with limited intake may benefit from a multivitamin or mineral supplement containing zinc to boost their immune system but should consult a health care provider first.

References

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Kathleen Zelman
Kathleen Zelman, MPH, RDN, is the nutrition director of WebMD.