Zinc: Immune Function, Recovery and Hormones

Zinc is an essential trace mineral involved in immune defence, tissue repair, protein synthesis and hormone metabolism. It is frequently marketed to athletes with claims about boosting testosterone and immunity. Some of these claims have a kernel of truth, but they mainly apply when zinc status is low. This article reviews what zinc genuinely does and how to meet your needs safely.

Why zinc matters for athletes

Zinc is a cofactor for hundreds of enzymes and is required for cell growth, DNA synthesis and the normal functioning of the immune system. For athletes, adequate zinc supports recovery from training through its role in protein synthesis and tissue repair. It also contributes to normal metabolism of carbohydrates, fats and protein, and to the maintenance of normal skin, hair and bones.

Zinc and immune function

Zinc plays a well-established role in immune health, and deficiency impairs the body's defences against infection. Some evidence suggests that zinc lozenges taken at the very onset of a cold may modestly shorten its duration, though results vary with dose and formulation. Importantly, this does not mean high-dose zinc supplements prevent illness in people who already have adequate intake. Maintaining sufficiency is the sensible goal, especially during heavy training when immune stress can increase.

Zinc and hormones

Zinc is involved in testosterone metabolism, and severe zinc deficiency can lower testosterone levels. This is the basis for claims that zinc supplements boost the hormone. However, in men who are not deficient, adding more zinc has not been convincingly shown to raise testosterone or improve strength. The hormonal benefit is essentially about correcting a shortfall, not exceeding normal levels. Products combining zinc with magnesium and vitamin B6, often marketed for hormones and sleep, rest on the same logic and are unlikely to help athletes whose intake of these nutrients is already sufficient.

Recovery and wound healing

Because zinc supports protein synthesis and cell division, it is important for wound healing and tissue repair. Athletes recovering from injury or surgery benefit from adequate zinc, but again, this reflects meeting requirements rather than megadosing. Prolonged heavy sweating and very high training volumes can nudge requirements upward, which is one reason endurance and combat-sport athletes on tight diets should pay attention to intake.

Who is at risk of deficiency?

Zinc deficiency is more likely in certain groups, including:

• Vegetarians and vegans, because plant sources contain phytates that reduce zinc absorption.
• Athletes on restricted or low-energy diets.
• Those with high sweat losses from prolonged training, which can increase zinc excretion.
• People with digestive disorders that impair absorption.

How much do you need?

Recommended intakes are approximately 8 mg per day for women and 11 mg per day for men, with higher needs during pregnancy and breastfeeding. The NIH sets a tolerable upper intake level of 40 mg per day for adults. Chronic intake above this can cause problems, most notably copper deficiency, because zinc and copper compete for absorption. High-dose zinc can also cause nausea and, over time, impair immune function, the opposite of the intended effect.

Food sources of zinc

• Oysters, by far the richest source, and other shellfish.
• Red meat and poultry, which provide well-absorbed zinc.
• Beans, lentils and chickpeas, useful plant sources.
• Nuts, seeds and wholegrains, though absorption is lower due to phytates.
• Dairy products such as cheese and yoghurt.

Practical guidance

Most omnivorous athletes who eat enough total food will meet their zinc needs without supplements. Plant-based athletes should pay attention to zinc-rich foods and preparation methods such as soaking, sprouting and fermenting, which reduce phytate content and improve absorption. If supplementing, stay well within the upper limit and avoid prolonged high doses to protect copper status. As with other micronutrients, zinc supplements deliver benefits mainly by correcting a genuine shortfall.

Key takeaways

• Zinc supports immunity, tissue repair, protein synthesis and hormone metabolism.
• Zinc lozenges may modestly shorten colds, but supplements do not prevent illness in people with adequate intake.
• Only deficiency lowers testosterone; extra zinc does not raise it in well-nourished men.
• Vegetarians, vegans and those on restricted diets are most at risk of low intake.
• Adults need about 8 to 11 mg daily; the upper limit is 40 mg per day.
• Excess zinc can cause copper deficiency, so avoid prolonged high doses.

References

1. Zinc — Health Professional Fact Sheet — NIH Office of Dietary Supplements
2. Scientific Opinion on Dietary Reference Values for zinc (2014) — EFSA Panel on Dietetic Products, Nutrition and Allergies
3. Hemilä H, Zinc Lozenges and the Common Cold: A Meta-Analysis, JRSM Open, 2017 — JRSM Open
4. Nutrition and Athletic Performance — Joint Position Statement (2016) — Academy of Nutrition and Dietetics, Dietitians of Canada, ACSM