Zinc

Why zinc matters for male physiology

Zinc is a cofactor for more than 300 enzymes. Several of them sit directly in the pathways this site is about: it is required for the conversion of cholesterol into testosterone in Leydig cells, it is a cofactor for 5-alpha reductase (the enzyme converting testosterone to DHT), it is required for normal LH secretion from the pituitary, and it is concentrated in prostatic fluid and semen at levels far higher than in blood.

That last point explains a practical detail: zinc is lost in semen, and it is also lost in sweat. Men who train heavily, sweat a lot, or ejaculate frequently have measurably higher requirements than the population reference intake assumes.

The evidence — with the important qualifier

The foundational human work is Prasad's research, which showed that experimentally induced marginal zinc deficiency in healthy young men reduced serum testosterone substantially within 20 weeks, and that repletion reversed it. Supplementation in zinc-deficient elderly men roughly doubled testosterone in the same body of work.

This is genuinely strong evidence — for correcting deficiency. It is not evidence that adding zinc to an already-replete man raises testosterone, and trials in zinc-sufficient populations consistently show no such effect. The distinction is the single most misrepresented point in supplement marketing around this mineral.

Deficiency is not rare. It is more common in vegetarians and vegans (phytates in grains and legumes bind zinc and reduce absorption), in heavy drinkers, in people with inflammatory bowel disease or coeliac disease, in older adults, and in men taking long-term diuretics or proton pump inhibitors.

Forms and absorption

Zinc oxide is the cheapest and the most common in low-cost multivitamins. Its absorption is poor and inconsistent — it requires stomach acid to dissociate and performs badly in older people and those on acid-suppressing medication.

Zinc bisglycinate (chelated to the amino acid glycine), zinc picolinate and zinc citrate all absorb substantially better and are gentler on the stomach. Bisglycinate is generally the best tolerated on an empty stomach.

Zinc gluconate and zinc sulphate sit in between, well absorbed but more likely to cause nausea.

Absorption is inhibited by phytates (whole grains, legumes), by calcium taken at the same time, and by high-dose iron. It is improved by taking zinc with a protein-containing meal.

The copper problem, and the upper limit

Zinc and copper compete for the same intestinal transporter. Sustained high-dose zinc supplementation induces metallothionein in gut cells, which preferentially binds copper and blocks its absorption. Chronic zinc intake at 50 mg per day or above can produce copper deficiency, which presents as anaemia unresponsive to iron, neutropenia, and — in severe long-standing cases — neurological damage.

EFSA sets the tolerable upper intake level at 25 mg per day from all sources for long-term use. Doses above this should be time-limited and, if extended, paired with 1–2 mg of copper. "ZMA"-type products commonly supply 30 mg zinc; that is fine short-term and worth reconsidering as a permanent daily habit.

Acute high doses cause nausea and vomiting, which is why zinc should be taken with food if it does not agree with you.