Verdict: Fix a real deficiency, otherwise extra zinc does not raise testosterone, strength or VO2max
Safety: Upper limit 40 mg a day; long-term high doses cause copper deficiency; may cause nausea
Key takeaways
Severe zinc restriction cut testosterone sharply in a small study, and supplementing marginally deficient older men raised it
In regularly exercising men with enough zinc in their diet, a high-dose zinc supplement (ZMA) did not change testosterone
The adult upper limit is 40 mg a day, and long-term high doses can cause copper deficiency with anaemia and nerve damage
Zinc is the most common ingredient in "testosterone booster" formulas, often sold as ZMA (zinc, magnesium aspartate and vitamin B6). The link between zinc and testosterone is real, but it works in one direction only: a deficiency lowers testosterone and fixing it restores levels. Adding more zinc to an adequate diet does not push testosterone higher.
What it is
Zinc is an essential mineral involved in hundreds of enzymes, immune function, wound healing, taste and sperm production. The recommended intake for adult men is about 11 mg a day (NIH Office of Dietary Supplements). Meat, shellfish (especially oysters), dairy, legumes, nuts and whole grains are good sources. People at higher risk of low zinc include vegetarians and vegans, people with gut disorders or heavy alcohol use, and older adults with poor diets. Athletes lose some zinc in sweat, but most who eat enough food meet their needs.
Does it raise VO2max?
Not in people with normal zinc status. VO2max is limited mainly by the heart and the oxygen-carrying capacity of the blood (see what limits VO2max), and no trial shows zinc supplements raise it in healthy, well-fed people. Testosterone does affect haemoglobin, but only a real deficiency would lower testosterone enough for zinc to matter (see testosterone, endurance training and VO2max).
Does it improve endurance performance?
There is no good evidence that it does in people who are not deficient. The interesting data are on hormones.
Prasad et al., 1996 — deficiency versus repletion
This study (Nutrition, 1996) had three parts:
- In 40 healthy men aged 20–80, testosterone correlated with zinc levels in blood cells.
- In four young men put on a zinc-restricted diet, serum testosterone fell from 39.9 to 10.6 nmol/L after 20 weeks.
- In nine marginally zinc-deficient older men, 3–6 months of zinc gluconate (459 µmol, about 30 mg of zinc a day) raised testosterone from 8.3 to 16.0 nmol/L.
The groups were tiny and there was no placebo arm, but the pattern is clear: zinc deficiency lowers testosterone, and correcting it brings levels back up.
Koehler et al., 2009 — ZMA in men with enough zinc
In 14 healthy, regularly exercising men whose diets already supplied about 12–23 mg of zinc a day, a high-dose ZMA supplement raised blood zinc but caused no significant change in total or free testosterone (Eur J Clin Nutr, 2009). If your diet already covers your needs, extra zinc is unlikely to change your hormones.
Immune function
Zinc is essential for immune cells, and deficiency increases infection risk. A meta-analysis by Hemilä (JRSM Open, 2017) of seven randomised trials found that zinc lozenges at more than 75 mg a day, taken from the start of a cold, shortened colds by about 33% on average. That is a short course of lozenges, not a reason to take high doses every day. For athletes who train hard and travel, enough sleep and energy intake matter more for staying healthy.
How it is used in studies
Deficiency trials used about 30 mg of zinc a day for months. Cold trials used lozenges for a few days. Common supplement forms are gluconate, citrate, picolinate and bisglycinate. Higher doses commonly cause nausea and stomach upset.
Side effects, safety and anti-doping
The tolerable upper intake level for adults is 40 mg a day from all sources. Long-term intake above it can interfere with copper absorption and cause copper deficiency, which leads to anaemia, low white blood cell counts and nerve damage (numbness, weakness and poor coordination). Long-term high doses can also lower HDL cholesterol and impair immune function. Zinc reduces absorption of quinolone and tetracycline antibiotics and penicillamine, so doses should be spaced apart.
Zinc is not banned in sport, but the products it comes in can be a problem. In an international study of 634 supplements, 14.8% contained anabolic steroids not listed on the label (Geyer et al., 2004), and FDA warnings link most adulterated muscle-building products to hidden steroids (Tucker et al., 2018). Under WADA's strict liability rule, an athlete is responsible for whatever is in their sample. Competitive athletes should use products certified by Informed Sport or NSF Certified for Sport.
This page is not medical advice. Men with symptoms of low testosterone, such as low libido, erectile problems, fatigue or loss of muscle, should see a doctor and get tested rather than self-treat.
Who might benefit
People with a diagnosed or likely zinc deficiency: those with very restricted diets, gut conditions affecting absorption, or heavy alcohol use. A doctor can check zinc status along with testosterone if symptoms suggest a problem. For healthy men eating a varied diet, food is enough. For training goals, creatine and adequate protein have much better evidence, and magnesium and vitamin D are other nutrients worth checking only if intake is low.
Bottom line
Zinc is a classic case of "only if you are deficient". Deficiency lowers testosterone and correcting it restores levels, but extra zinc does nothing for men with adequate intake and can cause copper deficiency at high doses. It will not raise VO2max. Compare other testosterone boosters such as boron and fenugreek, and see how to improve VO2max for what actually works.
Frequently asked questions
Does zinc increase testosterone?
Only if you are deficient. Prasad and colleagues found testosterone fell when young men's zinc intake was restricted and rose when marginally deficient older men took zinc. In men with adequate zinc, supplements have not raised testosterone.
How much zinc should a man take?
Adult men need about 11 mg a day, which most mixed diets provide. The upper limit from all sources is 40 mg a day, and higher doses should only be taken under medical supervision.
Does zinc help your immune system?
Zinc is essential for immune cells, and a meta-analysis found high-dose zinc lozenges started early shortened common colds by about a third. That is a short-term treatment, not a reason for daily high doses.
Can too much zinc be harmful?
Yes. Long-term intake above the upper limit can block copper absorption and cause copper deficiency, which leads to anaemia, low white cells and nerve damage. Weeks of high doses can also lower HDL cholesterol.
Sources
- Prasad AS, Mantzoros CS, Beck FW, Hess JW, Brewer GJ. Zinc status and serum testosterone levels of healthy adults. Nutrition. 1996;12(5):344–348.
- Koehler K, Parr MK, Geyer H, Mester J, Schänzer W. Serum testosterone and urinary excretion of steroid hormone metabolites after administration of a high-dose zinc supplement. Eur J Clin Nutr. 2009;63(1):65–70.
- 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. 2017;8(5):2054270417694291.
- NIH Office of Dietary Supplements. Zinc: Fact Sheet for Health Professionals.
- Geyer H, Parr MK, Mareck U, Reinhart U, Schrader Y, Schänzer W. Analysis of non-hormonal nutritional supplements for anabolic-androgenic steroids: results of an international study. Int J Sports Med. 2004;25(2):124–129.
- Tucker J, Fischer T, Upjohn L, Mazzera D, Kumar M. Unapproved pharmaceutical ingredients included in dietary supplements associated with US Food and Drug Administration warnings. JAMA Netw Open. 2018;1(6):e183337.