Zinc Deficiency: Who is at Risk and Why Athletes Need More

Zinc: A Trace Element with Major Physiological Consequences

Zinc is classified as a trace element, meaning the body requires it in relatively small quantities, but "trace" belies its importance. Over 300 enzymes depend on zinc as a catalytic cofactor, and more than 2,000 transcription factors require zinc for structural stability (the "zinc finger" domains found throughout the genome). Zinc deficiency — even mild, subclinical deficiency — has measurable consequences across multiple physiological systems.

Zinc and Immune Function

Zinc's role in immune function is well-established and multifaceted. It is required for the development and maturation of T lymphocytes in the thymus — without adequate zinc, thymic involution accelerates and T-cell output is reduced. Zinc also directly inhibits the replication of several respiratory viruses, including rhinovirus (the most common cause of the common cold), through direct antiviral mechanisms at the receptor binding site.

A Cochrane review of zinc lozenges and syrup for the common cold (updated 2013) found significant reductions in both the duration and severity of cold symptoms when zinc was taken within 24 hours of symptom onset. The form and dose are critical: zinc acetate and zinc gluconate in lozenge form deliver zinc directly to the oropharynx at effective concentrations. Zinc supplements swallowed as tablets may not achieve the same antiviral effect in the upper respiratory tract.

Zinc deficiency is associated with impaired neutrophil function, reduced natural killer cell activity, and shifts in the Th1/Th2 balance that can compromise both infection response and immune regulation.

Zinc and Testosterone

Zinc is required at two points in testosterone synthesis: as a cofactor for enzymes in the steroidogenesis pathway, and in the functioning of the hypothalamic-pituitary-gonadal axis. A landmark study by Prasad et al. (1996) demonstrated that marginal zinc restriction in healthy young men over 20 weeks reduced serum testosterone by approximately 75% — a dramatic effect that was fully reversed by zinc supplementation. Conversely, supplementing with 25 mg of zinc for six weeks in men with subnormal testosterone increased levels significantly.

The effect of zinc supplementation on testosterone appears most pronounced in zinc-deficient individuals. In men with replete zinc status, supplementation does not dramatically increase testosterone further. This is a consistent pattern in micronutrient research: supplementation corrects deficiency; it does not create a supraphysiological effect in replete individuals.

Taste, Smell, and Wound Healing

Zinc is required for the function of gustin (carbonic anhydrase VI), a zinc-dependent enzyme essential for taste perception. Zinc deficiency is a well-recognised cause of hypogeusia (reduced taste acuity) and hyposmia (reduced sense of smell). This connection was rediscovered during the COVID-19 pandemic: post-viral anosmia and dysgeusia prompted renewed interest in zinc's role in olfactory and gustatory receptor maintenance.

Zinc is also essential for wound healing: it is required for cell proliferation, collagen synthesis, and inflammatory regulation. Chronic wounds that fail to heal are frequently associated with zinc deficiency, and surgical patients with low zinc status have poorer healing outcomes.

Who Is at Risk

Vegans and vegetarians are at substantially higher risk of zinc deficiency. Phytates in plant foods — particularly whole grains, legumes, and seeds — bind zinc in the gut and inhibit absorption. The absorption of zinc from a plant-based diet may be 30–40% lower than from an omnivore diet of equivalent zinc content. Soaking, fermenting, or sprouting phytate-rich foods partially reduces this inhibition.

Athletes with high training volumes, particularly endurance athletes, lose significant zinc in sweat. Studies consistently document lower zinc status in endurance athletes compared to sedentary individuals. The increased inflammatory load of heavy training also increases zinc turnover.

Older adults absorb zinc less efficiently due to reduced gastric acid production and changes in intestinal transport proteins.

Bioavailability and Forms

Zinc oxide, one of the cheapest forms, has poor bioavailability. Zinc bisglycinate, zinc picolinate, and zinc citrate are better absorbed. Zinc carnosine (a chelate with L-carnosine) has specific evidence for supporting gastrointestinal mucosal integrity. For general supplementation, zinc bisglycinate at 15–25 mg elemental zinc per day is well-tolerated and well-absorbed.

The Copper Depletion Warning

Zinc and copper compete for absorption via the same transport protein (Zip4/hephaestin pathway) in the intestine. Chronic supplementation with zinc doses above 40 mg per day can progressively deplete copper, leading to copper deficiency anaemia and neurological complications. At doses of 25 mg or below, this is unlikely to be a practical concern for most adults, but long-term supplementation at higher doses warrants either dietary attention to copper-rich foods (liver, shellfish, nuts, seeds) or inclusion of a small copper supplement.