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.
(See also Overview of Dietary Supplements.)
Zinc has been claimed to reduce cold symptoms, help infants recover from infectious diseases, slow progression of age-related macular degeneration, and help wound healing.
Mild zinc deficiency impairs growth in children and can be corrected with zinc supplementation (1, 2). Zinc has been suggested to increase insulin sensitivity.
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 (3). 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 (3). 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 (3).
There is strong evidence that, in developing countries, supplements containing zinc 20 mg and 20 mg iron taken once/week, when given for the first 12 months of life, reduce infant mortality due to diarrhea and respiratory infections (4). A 2016 Cochrane review found that zinc supplementation may be beneficial to treat diarrhea in zinc-deficient or malnourished children who are over 6 months old (5). 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 (6-7). Clinical data on zinc for treatment of diabetes are emerging. A 2019 systematic review and meta-analysis of 32 randomized placebo controlled trials (1700 subjects) in patients with prediabetes or diabetes, obesity or overweight, and pregnant women with prediabetes or diabetes, found a significant decrease in fasting glucose of 14 mg/dL (0.8 mmol/L) and HbA1C of 0.55% (8).
Zinc is generally safe, but toxicity can develop if high doses are used (see page 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.
Mayo-Wilson E, Junior JA, Imdad A, et al: Zinc supplementation for preventing mortality, morbidity, and growth failure in children aged 6 months to 12 years of age. Cochrane Database Syst Rev, 5:CD009384, 2014. doi: 10.1002/14651858.
Lassi ZS, Kurji J, Oliveira CS: Zinc supplementation for the promotion of growth and prevention of infections in infants less than six months of age. Cochrane Database Syst Rev 4:CD010205, 2020. doi: 10.1002/14651858.CD010205.pub2.
Singh M, Das RR: Zinc for the common cold. Cochrane Database Syst Rev 6:CD001364, 2013. doi: 10.1002/14651858.CD001364.pub4.
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. doi: 10.1093/jn/133.12.4150.
Lazzerini M, Wanzira H: Oral zinc for treating diarrhoea in children. Cochrane Database Syst Rev 12:CD005436, 2016. doi: 10.1002/14651858.CD005436.pub5.
Chew EY, Clemons TE, Agron E, et al: Long-term effects of vitamins C and E, beta-carotene, and zinc on age-related macular degeneration: AREDS report no. 35. [published correction appears in Ophthalmology 123(12 ):2634, 2016]. Ophthalmology 120(8):1604-11.e4, 2013. doi:10.1016/j.ophtha.2013.01.021.
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. doi: 10.1001/jamaophthalmol.2013.7376.
Wang X, Wu W, Zheng W, et al: Zinc supplementation improves glycemic control for diabetes prevention and management: a systematic review and meta-analysis of randomized controlled trials. Am J Clin Nutr 110(1):76-90, 2019. doi: 10.1093/ajcn/nqz041.
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
National Institutes of Health (NIH), National Center for Complementary and Integrative Health: Information on some complementary health approaches for the common cold, including zinc, vitamin C, echinacea, probiotics, nasal saline irrigation, buckwheat honey, geranium extract, and garlic
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