The bottom line:
- Zinc is an essential micronutrient which plays a role in the regulation of immune function.
- Zinc deficiency is common. The World Health Organisation (WHO) estimates that up to one third of the world’s population is deficient in zinc(5).
- In Australia, zinc deficiency is more common in older men(6).
- Several studies suggest that zinc may assist with fighting respiratory tract infection such as common cold and flu (read on to learn more).
Zinc is an essential micronutrient which plays a role in the regulation of immune function. A substantial amount of scientific literature has documented the beneficial role of zinc in fighting respiratory tract infections such as common cold and flu. This review is intended to summarise available research on the role of zinc in immunity and respiratory infection.
In 2017, a large meta-analysis was conducted reviewing seven randomised, double-blind, placebo-controlled clinical trials of robust methodological quality including 575 participants with naturally acquired common cold. The seven clinical trials were conducted by six different research groups over three decades and all seven clinical trials concluded that supplementation with oral zinc lozenges decreased common cold duration by at least 33%(1).
In 2012, a systematic review and meta-analysis of 17 trials involving a total of 2121 participants found moderate quality evidence to suggest that orally administered zinc reduced the duration of symptoms of the common cold compared to placebo(2).
A similar systematic review conducted by Singh & Das in 2013 included 16 therapeutic trials (randomised, double-blind and placebo controlled trials) and found that zinc administered within 24 hours of symptom onset reduced the duration of common cold symptoms in healthy people, regardless of the type of preparation used (lozenges, syrup or tablets), and concluded that tablet forms of zinc were better tolerated than lozenges. It should be noted that the majority of research to date has been conducted using high dose zinc lozenges (greater than 75mg elemental zinc per day) and further clinical trials are needed to further evaluate the benefits of zinc tablets(3). In 2009, a clinical trial to assess the efficacy of zinc tablets in the treatment and prevention of common cold in 200 primary school children showed that regular supplementation with zinc tablets (equivalent to 10mg elemental zinc) reduced the frequency and severity of common colds and resulted in less missed school days and less antibiotic use when compared to children taking placebo(4).
Furthermore, zinc deficiency is common. The World Health Organisation (WHO) estimates that up to one third of the world’s population is deficient in zinc and an Australian study of 497 Tasmanian adults showed that zinc deficiency was present in 18% of men over the age of 50 and 30% of men over the age of 70(5).
A number of clinical trials have documented effects of zinc supplementation in improving cell-mediated immunity and reducing respiratory infection in elderly populations. A clinical trial conducted in 2015 involving more than a hundred nursing home residents in Italy demonstrated that 25mg elemental zinc (as zinc sulfate) improved cell-mediated immune response by increasing the number of T helper cells and cytotoxic T cells(6). Another study showed that supplementation with 45mg elemental zinc per day (as zinc gluconate) significantly reduced the occurrence of infections in older people, including respiratory infection, over a 12 month period(7).
Given the prevalence of zinc deficiency in the general community; the clear association between zinc deficiency and the incidence of respiratory infection; and the benefits of zinc supplementation in reducing infectious disease, assessment of zinc status and appropriate supplementation with zinc should be considered an issue of public health concern.
- Hemilä H. Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. JRSM Open [Internet]. 2017;8(5):205427041769429. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5418896/
- Science M, Johnstone J, Roth D, Guyatt G, Loeb M. Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials. Canadian Medical Association Journal [Internet]. 2012;184(10):E551-E561. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3394849/
- Singh M, Das R. Zinc for the common cold. Cochrane Database of Systematic Reviews [Internet]. 2013;. Available from: https://pubmed.ncbi.nlm.nih.gov/23775705/
- Vakili R, Vahedian M, Khodaei G, Mahmoudi M. Effects of zinc supplementation in occurrence and duration of common cold in school aged children during cold season: a double-blind placebo-controlled trial. Iranian Journal of Paediatrics [Internet]. 2009;19(4):376-380. Available from: https://www.sid.ir/en/journal/ViewPaper.aspx?ID=164643
- Beckett J, Ball M. Zinc status of northern Tasmanian adults. Journal of Nutritional Science [Internet]. 2015;4. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4463943/
- Fortes C, Forastiere F, Agabiti N, Fano V, Pacifici R, Virgili F et al. The Effect of Zinc and Vitamin A Supplementation on Immune Response in an Older Population. Journal of the American Geriatrics Society [Internet]. 1998;46(1):19-26. Available from: https://onlinelibrary.wiley.com/doi/full/10.1111/j.1532-5415.1998.tb01008.x
- Prasad A, Beck F, Bao B, Fitzgerald J, Snell D, Steinberg J et al. Zinc supplementation decreases incidence of infections in the elderly: effect of zinc on generation of cytokines and oxidative stress. The American Journal of Clinical Nutrition [Internet]. 2007;85(3):837-844. Available from: https://pubmed.ncbi.nlm.nih.gov/17344507/