zinc

Zinc is an essential mineral found in cells throughout the body. According to the NIH Office of Dietary Supplements, it helps the immune system fight off bacteria and viruses, is used to make DNA and proteins, supports normal growth and development during pregnancy, infancy, childhood, and adolescence, and contributes to wound healing and a normal sense of taste. Most people in the United States get enough zinc from food (oysters, meat, poultry, seafood such as crab and lobster, fortified breakfast cereals, beans, nuts, whole grains, eggs, and dairy), so supplements are mainly relevant for groups at risk of low intake.

Evidence varies by use, and most uses are not firmly established. For the common cold, NIH says some studies suggest zinc lozenges or syrup taken at the start of a cold may speed recovery, but these products don't seem to affect symptom severity, and more study is needed to determine the best dose, form, timing, and duration. For age-related macular degeneration, large studies (AREDS/AREDS2) found that daily supplements combining zinc with copper and certain antioxidants lowered the risk of progressing to advanced AMD in older people already at high risk — this is not prevention in healthy eyes. Zinc may reduce the duration of diarrhea in children in lower-income settings, many of whom are zinc-deficient or malnourished; it is not clear it helps children who already get enough zinc. For type 2 diabetes, NIH says some research suggests zinc might help lower blood sugar and cholesterol, but more research is needed before it can be recommended. The NIH zinc fact sheets do not present zinc as a treatment for COVID-19 and refer readers to a separate NIH resource.

Recommended Dietary Allowances are about 11 mg/day for adult men and 8 mg/day for adult women (more in pregnancy and breastfeeding); these are total daily needs usually met by diet. Supplements come in forms such as zinc sulfate, zinc acetate, and zinc gluconate, and NIH notes it is not clear whether one form is better than another. The Tolerable Upper Intake Level from all sources combined (food, beverages, supplements, and medications) is 40 mg/day for adults, and lower for teens and children; this limit does not apply to people taking supplemental zinc under a doctor's care. Talk to a doctor, pharmacist, or registered dietitian before starting zinc — especially if you are pregnant, have a health condition, or take medications.

Zinc from food is generally safe and rarely reaches harmful levels. Too much supplemental zinc can be harmful: taking too much for a long time can interfere with copper absorption, lower immunity, and lower HDL ("good") cholesterol, and very high doses can also reduce magnesium absorption. Chronic, excessive use of zinc-containing denture creams (well beyond label directions) has caused copper deficiency and neurological problems such as loss of coordination, numbness, and weakness in the arms, legs, and feet. Stay within the 40 mg/day adult upper limit unless a clinician directs otherwise. Some over-the-counter products labeled as homeopathic cold remedies, plus some intranasal sprays and denture creams, contain zinc; NIH lists these among zinc-containing products to be aware of.

Signs of getting too much zinc include nausea, dizziness, headaches, upset stomach, vomiting, and loss of appetite. Taking too much for a long time can lead to lower immunity, lower HDL cholesterol, and low copper levels; very high supplemental doses can also reduce the body's absorption of magnesium.

Zinc can interact with several medications. Quinolone antibiotics (such as ciprofloxacin) and tetracycline antibiotics can have reduced absorption when taken with zinc — NIH suggests taking the antibiotic at least 2 hours before, or 4–6 hours after, a zinc supplement. Zinc can reduce absorption of penicillamine (used for rheumatoid arthritis and Wilson disease), so the two should be taken at least 1 hour apart. Long-term use of thiazide diuretics (such as hydrochlorothiazide and chlorthalidone) increases urinary zinc loss and can lower zinc levels over time. Tell all your health care providers about any supplements you take.