Zinc benefits

How is a role in the body separated from the benefit of a supplement?

Zinc takes part in the working of hundreds of enzymes, in immune function, wound healing, and DNA and protein synthesis. These roles show that zinc is necessary; they do not show that someone with adequate levels will carry out these functions better by taking more. Under each of the headings below, who was studied, which outcome was measured and what the limit is are stated together. ^[1]

When does a supplement help if there is a deficiency?

In people with zinc deficiency, outcomes are clearly affected: diarrhea and growth delay in children, taste and smell changes in adults, and delayed wound healing in older adults can occur. In these situations, correcting the deficiency is a treatment directed at the cause. ^[1]

In acute childhood diarrhea, the World Health Organization and UNICEF recommend short-term zinc support; however, most of these studies were done in low-income countries where deficiency is common, and the effect may be limited in well-nourished children. ^[1] This example shows that who benefits from the same intervention depends on the population.

Does zinc shorten a cold?

This is the most studied question. The 2024 Cochrane review evaluated 34 studies comparing zinc with placebo (15 on prevention, 19 on treatment; 8,526 participants). Half of the studies used lozenges; the most commonly used form was gluconate; zinc gluconate was given at 45–276 mg per day for 4.5–21 days. ^[2]

Prevention: Zinc was reported to reduce the risk of catching a cold very little or perhaps not at all (RR 0.93 in 9 studies; 95% CI 0.85–1.01; low certainty).

Treatment: When used after a cold had started, the mean duration may be shortened by 2.37 days (95% CI −4.21 to −0.53; 8 studies, 972 participants). The certainty of the evidence is low, and the heterogeneity between studies is very high (I² 97%). There is no firm result that symptom severity differs. In treatment studies, non-serious side effects probably increase in those using zinc (RR 1.34; 95% CI 1.15–1.55; 16 studies; moderate certainty). ^[2]

NIH also describes the results as inconsistent: zinc in lozenge or syrup form appears to shorten duration, but not reduce severity, if taken shortly after symptoms begin. No firm recommendation can be given for the most suitable amount, form and timing. ^[1]

These results were obtained in children and adults, in lozenge, syrup or similar forms, under specific study conditions. The answer to “how much, how often” is not given on this page; the frequencies used in the studies are not a usage instruction.

Does zinc work in age-related macular degeneration?

The AREDS study followed 3,640 participants aged 55–80 for a mean of 6.3 years. Participants were given daily antioxidants (vitamin C, vitamin E, beta carotene), zinc (80 mg, zinc oxide) and copper (2 mg), both, or placebo. When antioxidants and zinc were given together, progression to advanced macular degeneration decreased compared with placebo (OR 0.72; 99% CI 0.52–0.98). For zinc alone, the OR was 0.75 and did not pass the significance level set by the study (99% CI 0.55–1.03). ^[3]

The AREDS2 study (4,203 participants, aged 50–85) reported that adding lutein and zeaxanthin and omega-3 fatty acids did not further reduce the risk of advanced macular degeneration; removing beta carotene or lowering the amount of zinc also had no marked effect on progression. ^[4] NIH interprets the lower-zinc-amount result as a preliminary finding because of the number of participants. ^[1]

These results apply to people with a diagnosis of macular degeneration or at risk of progression. They are not evidence supporting zinc for eye protection in healthy people. Use for this purpose is done under an eye physician’s monitoring; the amount of zinc used in AREDS was above the upper limit and was given together with copper.

Is zinc good for acne?

The systematic review and meta-analysis by Yee and colleagues looked at two questions: was the serum zinc level of people with acne lower than that of controls, and was zinc treatment effective in acne? Serum zinc was found to be significantly lower in people with acne; in those receiving zinc treatment, a significant improvement was seen in the number of inflammatory papules, and the frequency of side effects did not differ from the comparison groups. ^[5]

There are two limits here. Low serum zinc does not prove that zinc deficiency causes acne; the association is observational. The effect of zinc has also been shown with specific measures such as papule count; it does not mean it replaces standard treatments for every type of acne and every person. The decision on amount and form in acne treatment belongs to the dermatologist.

Does zinc work for COVID-19?

In the COVID A to Z study, 214 adult outpatients with SARS-CoV-2 were divided into four groups: 50 mg of zinc gluconate for 10 days, a high amount of vitamin C, both, or usual care. The time to reach a 50% reduction in symptoms was a mean of 6.7 days in the usual care group and 5.9 days in the zinc gluconate group; the difference was not significant (overall P = 0.45). The study was stopped early because of the low probability of showing benefit. ^[6]

The study also has limits: an open-label design (participants and investigators knew who received what), an outpatient group, and conduct within a single health system. This result does not mean “zinc can have no effect at all in COVID-19”; however, no benefit has been shown in outpatients.

Does zinc increase testosterone?

The systematic review by Te and colleagues examined 38 articles (8 clinical, 30 animal studies). The result was: zinc deficiency lowers testosterone level and supplements can raise it; however, the degree of the effect can vary with baseline zinc and testosterone level, zinc form, amount and duration. ^[7]

Most of the studies in the review (30) are animal studies; the number of clinical studies is eight. That supplements would raise testosterone in a man with adequate zinc status is not supported by these data. If there are symptoms of low testosterone, diagnosis and investigation of the cause are a physician’s job; zinc alone is not a testosterone treatment.

Summary of the evidence

What to know before supplementing

None of these results means “everyone should take zinc.” Zinc at 50 mg and above taken for weeks can impair copper absorption and reduce immune function; NIH gives the adult upper limit as 40 mg/day. ^[1] Safety and drug interactions are detailed on the hub page.

This guide does not recommend a personal dose; the use of zinc for a specific disease is the physician’s responsibility.