(See also Overview of Dietary Supplements.)
Zinc, a mineral, is required in small quantities (adult RDA of 8 to 11 mg/day) for multiple metabolic processes. Dietary sources include oysters, beef, and fortified cereals.
Zinc has been claimed to reduce cold symptoms, help infants recover from infectious diseases, and slow progression of age-related macular degeneration.
Some experts believe that when taken soon after cold symptoms develop, zinc taken as zinc gluconate or acetate lozenges can shorten the course of the common cold (1). A 2013 Cochrane review of 16 therapeutic trials (1387 participants) and 2 preventive trials (394 participants) demonstrated that zinc reduced the duration (in days) but not the severity of common cold symptoms (1). Although the proportion of participants with symptoms after 7 days of treatment was significantly smaller than those in the control groups, adverse effects, such as bad taste and nausea, were higher in the zinc group and should be taken into consideration (1).
There is strong evidence that in developing countries, supplements containing zinc 20 mg and 20 mg iron taken once/wk, when given for the first 12 mo of life, reduce infant mortality due to diarrhea and respiratory infections (2). There is also strong evidence that supplements containing zinc 40 to 80 mg and antioxidants (vitamin C and E and lutein/zeaxanthin) taken once/day slow progression of moderate to severe atrophic (dry form) age-related macular degeneration (3-4).
Zinc is generally safe, but toxicity can develop if high doses are used (see Zinc Toxicity). The common adverse effects of zinc lozenges include nausea, vomiting, diarrhea, mouth irritation, mouth sores, and bad taste. Because zinc is a trace metal and can remove other necessary metals from the body, zinc lozenge dose should not exceed 75 mg day (total dose, regardless of dosing frequency) for 14 days. Zinc sprays may cause nose and throat irritation.
Singh M, Das RR. Zinc for the common cold. Cochrane Database Syst Rev 6:CD001364, 2013.
Baqui AH, Zaman K, Persson LA, et al. Simultaneous weekly supplementation of iron and zinc is associated with lower morbidity due to diarrhea and acute lower respiratory infection in Bangladeshi infants. J Nutr 133(12):4150-4157, 2003.
Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8. Arch Ophthalmol 119(10):1417-1436, 2001.
The Age-Related Eye Disease Study 2 (AREDS2) Research Group, Chew EY, Clemons TE, et al. Secondary analyses of the effects of lutein/zeaxanthin on age-related macular degeneration progression: AREDS2 report No. 3. JAMA Ophthalmol 132(2):142-149, 2014.