Zinc Supplement: Who Needs One, What the Evidence Shows, and What It Means for Athletes

Key Takeaways

A zinc supplement is mainly a tool for correcting low intake or deficiency. Zinc homeostasis is tightly regulated, which makes zinc status hard to assess, and plasma zinc has limitations as a marker.
In the United States, the recommended intake is 11 mg/day for men and 8 mg/day for women. The tolerable upper intake level is 40 mg/day in the US and 25 mg/day according to the European Food Safety Authority.
For the common cold, a 2024 Cochrane review found that zinc may make little or no difference to the risk of catching a cold, while zinc taken as treatment may shorten a cold by a mean of 2.37 days, based on low-certainty evidence and with probably more non-serious side effects than placebo.
Avoid intranasal zinc products. Intranasal zinc gluconate gel has been linked to loss of the sense of smell.
In my clinical experience, zinc is often taken pre-emptively or throughout the cold season, and some patients assume it can be megadosed in the way many people think of vitamin C. I would not recommend megadosing zinc, partly because of the risk of copper deficiency.
In my view, zinc does not need to be tested routinely. In my roughly ten years of clinical work, I have not seen zinc deficiency or zinc excess actively suspected behind a patient’s symptoms, and both may go unrecognised in practice.
Zinc citrate and zinc gluconate were absorbed similarly well in a head-to-head isotope study, and both were absorbed better than zinc oxide.
Long-term excess zinc can cause zinc-induced copper deficiency, which can present with anaemia, neutropenia and a spinal cord disorder that resembles vitamin B12 deficiency.
For athletes, one controlled trial of ZMA (zinc magnesium aspartate) found no improvement in training adaptations in resistance-trained men, and another found no statistically significant change in total or free testosterone in men whose diet already supplied enough zinc. Plant-based athletes are among those most worth checking.
In my assessment, athletic status by itself is not an additional indication for zinc. Correcting a deficiency is what may improve performance; in my view, current evidence does not justify additional zinc for performance when intake is already adequate.

Introduction: Why a Zinc Supplement Is Not a Default

Zinc is an essential trace element that takes part in over 300 enzymatic reactions, as well as in the regulation of gene expression and immune function.[1] It is also widely sold as an over-the-counter supplement.

Inadequate zinc intake is a genuine global problem. An analysis of national food supply data estimated that the global prevalence of inadequate zinc intake ranged from 12% to 66% depending on the methodological assumptions used, with the authors’ best-estimate model giving 17.3%.[2] A population-level estimate like this does not, however, mean that a healthy adult eating a varied diet needs a zinc supplement.

In practice, zinc has become something of a trend supplement. In my clinical experience, many patients take it pre-emptively, and some use it throughout the cold season. From a clinical perspective, though, a varied diet should come first: with a sufficiently varied diet, many people get enough zinc, and there is often no need for a supplement. In my view, the supplement more often worth taking for people in Finland is vitamin D; see Vitamin D Deficiency Symptoms.

This article covers how much zinc you need, who may benefit from a zinc supplement, what the evidence shows for colds and other uses, which forms are absorbed best, the safety limits, and what all of this means for athletes. For interpreting a serum zinc result in a training athlete, see Zinc in Athletes.

How Much Zinc Do You Need?

Reference values differ by authority. In the United States, the recommended dietary allowance is 11 mg/day for men and 8 mg/day for women.[1] The European Food Safety Authority (EFSA) sets its population reference intake according to dietary phytate intake, ranging from 9.4 to 16.3 mg/day for men and from 7.5 to 12.7 mg/day for women.[1]

The upper limits also differ. EFSA defines the tolerable upper intake level as 25 mg/day, whereas the US limit is 40 mg/day.[1] Excessive intake may lead to anaemia, neutropenia and zinc-induced copper deficiency.[1] The difference between the two limits matters most when zinc from several products, such as a multivitamin and a standalone zinc supplement, is combined.

Who Might Actually Need a Zinc Supplement?

Confirmed or Likely Deficiency

The basic indication is low zinc status. The difficulty is identifying it. Zinc homeostasis at the cellular, tissue and whole-body level is tightly controlled across a wide range of intakes, which makes both insufficiency and excess difficult to assess.[3] The Biomarkers of Nutrition for Development (BOND) expert panel recommends three measures for estimating zinc status: dietary zinc intake, plasma zinc concentration, and height-for-age in growing children.[3] Plasma zinc responds to severe dietary restriction and to supplementation, but the panel notes that it has limitations as a measure of zinc status.[3]

In practice, this means a single plasma zinc result is best interpreted together with diet history and the overall clinical picture.

In everyday practice, zinc rarely needs to be measured. It may appear in some broad trace-element laboratory panels, but in my view it does not need to be checked routinely, for example as part of periodic health checks. Testing may occasionally be indicated in rarer situations, such as a very broad diagnostic work-up or the investigation of rare diseases in specialist care. In my roughly ten years of clinical experience, I have not seen zinc deficiency actively looked for as the explanation behind a patient’s symptoms. Because the list of alternative diagnoses is long, a zinc deficiency, if present, could in my view easily go unrecognised in clinical practice.

Vegetarians and Vegans

A systematic review included 34 studies, 26 of which were pooled in meta-analyses. Compared with non-vegetarians, people following habitual vegetarian diets had dietary zinc intakes that were 0.88 mg/day lower and serum zinc concentrations that were 0.93 µmol/L lower.[4] The effect was greater in females, in vegetarians from developing countries and in vegans.[4] For a well-planned plant-based diet, this is primarily an argument for paying attention to zinc-rich foods; a supplement becomes relevant when intake remains low or deficiency is suspected.

Children With Diarrhoea in High-Risk Settings

Zinc may also benefit children with diarrhoea in settings where deficiency is common. A Cochrane review found that in children older than six months with acute diarrhoea, zinc may shorten the average duration of diarrhoea by around half a day (mean difference −11.46 hours; 9 trials, 2,581 children; low-certainty evidence), but it increased the risk of vomiting (RR 1.57).[5] The authors concluded that zinc may help children aged six months or more in areas where zinc deficiency or malnutrition is common, and that the evidence does not support its use in children under six months, in well-nourished children, or in settings where children are at low risk of zinc deficiency.[5]

Zinc is one component of the AREDS supplement formula for age-related macular degeneration (AMD). A 2023 Cochrane review concluded, with moderate-certainty evidence, that antioxidant vitamin and mineral supplementation using the AREDS combination of vitamins C and E, beta-carotene and zinc probably slows progression to late AMD.[6] In the AREDS trial, zinc was associated with a higher risk of genitourinary problems in men.[6] The review covered people who already had AMD, so it does not show a benefit of zinc for eye health in people without the disease.

Zinc Supplement for the Common Cold

The most recent Cochrane review identified 34 studies of zinc for preventing or treating colds. For prevention, zinc may make little or no difference to the risk of developing a cold (RR 0.93, 95% CI 0.85 to 1.01; 9 studies, 1,449 participants; low-certainty evidence).[7] For treatment, zinc may shorten the mean duration of a cold by 2.37 days (95% CI −4.21 to −0.53; 8 studies, 972 participants; low-certainty evidence), although heterogeneity between the trials was very high (I² = 97%).[7] Zinc used as treatment probably increases the risk of non-serious adverse events (RR 1.34; 16 studies, 2,084 participants; moderate-certainty evidence).[7] Half of the studies (17 of 34) tested lozenges, most often zinc gluconate, which was given at doses between 45 and 276 mg/day for between 4.5 and 21 days.[7]

A narrower analysis focused on high-dose zinc acetate lozenges. Pooling individual patient data from three placebo-controlled trials in which the lozenges provided more than 75 mg/day of elemental zinc, it estimated that colds were 2.94 days shorter (95% CI 2.1 to 3.8) in the two-stage analysis and 2.73 days shorter in the one-stage analysis.[8] The effect was not modified by allergy status, smoking, baseline cold severity, age, sex or ethnic group.[8]

Two practical points follow. First, more than 75 mg/day of elemental zinc is well above both the EFSA and US upper limits,[1][8] and in the Cochrane review, zinc gluconate was given for between 4.5 and 21 days.[7] Second, the overall certainty of the evidence remains low, and non-serious side effects are probably more common with zinc than with placebo.

Avoid intranasal zinc. In a case series of 17 patients who developed impaired smell after using intranasal zinc gluconate gel, all reported sniffing deeply when applying it, followed by an immediate burning sensation and loss of smell within 48 hours; 7 of the 17 never developed symptoms of a respiratory infection.[9] The authors attributed the syndrome to exposure of the olfactory epithelium to zinc.[9]

From a clinical perspective, zinc has become closely linked with the common cold, at least in Finland, where zinc tablets and oral zinc sprays have reached cold patients’ awareness alongside vitamin C. I encounter this most often in occupational health care and with patients who have a cold. A typical story at the clinic is that the patient has taken vitamin C together with zinc tablets or an oral zinc spray in the hope of recovering faster, and many ask whether it helps. I usually answer that it may shorten a cold, but that I cannot guarantee any effect. For context, the evidence above shows a possible shortening of a cold, with low certainty and probably more non-serious side effects than placebo, and no treatment study reported on serious adverse events.[7]

Part of this may stem from the idea of vitamin C megadosing. In 1970, Linus Pauling, a Nobel laureate in chemistry who also received the Nobel Peace Prize, wrote a book on vitamin C and concluded that gram doses would be beneficial against colds; his work went on to greatly increase public interest in vitamin C.[10] In my clinical experience, many patients have been left with the idea that vitamin C can be taken in very large doses during a cold, and some seem to assume that the same applies to zinc. As a result, some patients take excessive amounts of zinc in the hope of recovering faster. Some may even be aware that an overdose is possible but reason that a cold lasts only a short time, so a brief period of high doses would not matter. In my view, this is not advisable, and I would not recommend megadosing zinc, partly because of the risk of copper deficiency described below. Copper deficiency can also easily be missed in clinical practice, but the possibility is known, and high-dose zinc is not entirely neutral. I may therefore tell patients that zinc cannot be megadosed in the way many people think of vitamin C.

Which Form of Zinc Supplement Is Best?

Zinc supplements are sold as several different zinc salts, and human data comparing their absorption are limited.[11] In a randomised, double-masked crossover study in 15 healthy adults given 10 mg of zinc without food, median fractional absorption was 61.3% from zinc citrate, 60.9% from zinc gluconate and 49.9% from zinc oxide; absorption from oxide was significantly lower than from the other two (P < 0.01), and three participants absorbed little or no zinc from the oxide form.[11]

The practical message is that zinc gluconate or zinc citrate is a reasonable default, while zinc oxide is the least reliable of the three. When comparing products, check the label for the amount of elemental zinc rather than the weight of the zinc salt.

Safety: Stomach Upset and Zinc-Induced Copper Deficiency

Gastrointestinal Side Effects

High-dose zinc supplements can cause nausea and abdominal discomfort. In a double-blind crossover trial, 47 healthy volunteers took 50 mg of elemental zinc as zinc sulphate three times a day for six weeks. Symptoms including headache, abdominal cramps, nausea, loss of appetite and vomiting were reported by 84% of the women and 18% of the men, and the authors suggested that the gastric discomfort may be related to body weight, because symptoms were reported by the lower-weight volunteers.[12] Plasma copper did not change significantly during the six weeks of supplementation.[12]

Copper Deficiency

The more serious risk of long-term excess is zinc-induced copper deficiency.[1] The haematological features of copper deficiency include anaemia and neutropenia, and its most common neurological form is a myelopathy that presents with a spastic gait and prominent sensory ataxia.[13] Known causes of acquired copper deficiency include previous gastric surgery, excessive zinc ingestion and malabsorption.[13] The clinical and imaging findings resemble the subacute combined degeneration of vitamin B12 deficiency, and the two deficiencies can coexist.[13] Copper supplementation resolves the anaemia and neutropenia promptly and completely and may prevent further neurological deterioration, but neurological improvement, when it occurs, is often subjective.[13] In someone with prolonged excessive zinc intake, a full blood count and assessment of copper status may be appropriate when the history or symptoms raise concern about copper deficiency, bearing in mind that the neurological syndrome may be present without the blood-count changes;[13] see CBC Blood Test for what it covers.

In my roughly ten years of clinical work, I have not seen a situation in which a patient’s symptoms were suspected to be caused by excessive zinc intake. From a clinical perspective, the clinical picture is recognised, but it is not part of a clinician’s everyday work, and in practice the symptoms can be difficult to connect to zinc. In my view, such cases may therefore be underdiagnosed, and many may go unrecognised.

What It Means for Athletes: Do You Need a Zinc Supplement?

Lower Serum Zinc Is Not the Same as Deficiency

A meta-analysis of cross-sectional studies found that athletes had serum zinc concentrations 0.93 µmol/L lower than control populations, despite dietary zinc intakes 2.57 mg/day higher, which the authors interpreted as suggesting that athletes have a higher zinc requirement than physically inactive people.[14] Plasma or serum zinc, however, has limitations as a marker of zinc status,[3] so a low-normal value in an athlete is not automatically a deficiency. The full interpretation framework, including test timing, is covered in Zinc in Athletes and Preparing for a Blood Test.

ZMA and Testosterone

Products containing ZMA are often advertised as raising testosterone.[15] In a double-blind trial, 42 resistance-trained men took ZMA or a placebo 30–60 minutes before sleep during 8 weeks of standardised resistance training. Serum zinc rose by a non-significant 11–17%, and the authors concluded that ZMA did not appear to enhance training adaptations.[16] A second study in 14 healthy, regularly exercising men with a baseline zinc intake of 11.9–23.2 mg/day found that ZMA increased serum zinc and urinary zinc excretion but produced no significant change in serum total or free testosterone.[15] The authors concluded that ZMA has no significant effect on serum testosterone in people who consume a zinc-sufficient diet.[15]

Zinc deficiency itself is a different matter, as discussed in Testosterone in Athletes. The distinction is the same as for iron: correcting a deficiency is not the same as boosting a normal level. For the magnesium side of ZMA, see Magnesium in Athletes.

Performance Claims

The International Olympic Committee (IOC) consensus statement on dietary supplements notes that products described as supplements serve several purposes, one of which is managing micronutrient deficiencies, but that among supplements marketed to enhance performance, only a few — including caffeine, creatine, specific buffering agents and nitrate — have good evidence of benefit.[17] Zinc is not among the supplements the statement names. The same statement stresses that some supplements can harm an athlete’s health, performance, livelihood or reputation if an anti-doping rule violation results, and strongly advises expert professional input before an athlete starts using supplements.[17] For a broader overview, see Which Supplements May Help Athletes.

In my experience, supplements are quite common in combat sports, and many athletes also take zinc. Most combat athletes I have known seem to rely on various multivitamins, but some take it to the next level and buy individual supplements to take separately, straight from the container, in the belief that this gives them an extra performance boost. I remember doing this myself when I was younger, long before I studied medicine; the idea was to make sure I was getting every trace element. In part this was understandable, because I was often dieting, and during very large calorie deficits my intake of every micronutrient was not necessarily adequate.

Colds During Heavy Training

Respiratory infections can interrupt training and competition, which makes zinc lozenges tempting. The evidence summarised above comes from common cold trials: zinc may shorten a cold when used as treatment, but it may make little or no difference to the risk of catching one.[7] For athletes, this evidence offers no clear justification for continuous high-dose zinc through the season; short-term treatment may shorten a cold, but the evidence is uncertain and not specific to athletes. Decisions about training while ill are covered in Exercise When Sick, and post-race infection risk in Immune Suppression After a Marathon.

Who Is Worth Checking?

In the general population, vegetarian diets, and especially vegan diets, have been associated with lower dietary zinc intake and serum zinc concentrations,[4] so athletes following these diets are one group worth assessing for zinc intake. Other dietary and clinical risk situations are discussed in the companion article on zinc in athletes linked above. For these athletes, a dietary review comes first; a zinc supplement is a targeted correction, not a performance aid.

In my view, athletes do not generally have a special reason to take a zinc supplement. In my assessment, athletic status alone does not create an indication for routine zinc supplementation, although athletes’ exact zinc requirements have not been established.[14] Many multivitamins already contain zinc, which is fine, but I would not recommend doubling up on multivitamins as an athlete either. It is understandable that athletes often want extra trace elements just in case, because they want to make sure their performance is not held back by a missing micronutrient. From a clinical perspective, however, it is correcting a deficiency that may improve performance; in my view, current evidence does not justify additional zinc supplementation for performance when zinc intake is already adequate.

Conclusion: A Zinc Supplement Is a Targeted Tool

The evidence for a zinc supplement is real but narrow. It corrects deficiency, it may benefit children with diarrhoea in high-risk settings, it is one component of the AREDS combination supplement that probably slows progression to late AMD, and it may shorten a common cold by a mean of 2.37 days when taken as treatment, although that evidence is of low certainty. It may make little or no difference to the risk of catching a cold, and in men who already eat enough zinc, ZMA did not significantly change testosterone.

The risks are equally specific: gastrointestinal symptoms at high doses, loss of smell with intranasal zinc, and copper deficiency with long-term excess. For most healthy adults and athletes eating a varied diet, food is the better starting point. A zinc supplement makes the most sense when intake is genuinely low, deficiency is confirmed or strongly suspected, or for short-term use during a cold, with total intake kept in view. In my own practice, a varied diet comes first, I would not recommend megadosing zinc, and I do not see athletic status alone as a reason to supplement it; for people in Finland, vitamin D is in my view the supplement more often worth taking.

Zinc Supplement: Who Needs One, What the Evidence Shows, and What It Means for Athletes

Table of Contents

Key Takeaways

Introduction: Why a Zinc Supplement Is Not a Default

How Much Zinc Do You Need?