Zinc raises testosterone

Zinc raised testosterone in most, though not all, studies of people who were low in zinc to begin with, and most of those studies were small. In two studies of men whose zinc was already adequate, one of them double-blind and placebo-controlled, testosterone did not change, and it did not change in a placebo-controlled trial that gave zinc together with folic acid. In 9 older men with marginal zinc deficiency, testosterone rose from 8.3 to 16.0 nmol/L over 3 to 6 months of zinc gluconate. In 20 men on hemodialysis for kidney failure, testosterone roughly doubled over 6 months on zinc acetate and did not change on placebo. A second double-blind trial of zinc acetate for 6 months, in 18 men on dialysis with low zinc, raised their zinc levels and found no change in testosterone.

The largest trial found was in women. In 116 postmenopausal women with low zinc levels and low sexual function, randomly assigned to zinc or to a control group, testosterone rose more in the zinc group. The published summary of that trial does not say whether the control group took a placebo, whether anyone was blinded, or what dose was used.

In men with adequate zinc, testosterone did not change. A double-blind, placebo-controlled trial of 42 resistance-trained men taking a zinc magnesium aspartate (ZMA) product for 8 weeks found no difference in testosterone or other hormones, and a study of 14 regularly exercising men on a zinc-sufficient diet found no change in total or free testosterone after taking ZMA. A 26-week placebo-controlled trial of folic acid plus zinc sulphate in 87 men, whose zinc status the abstract does not describe, also found no change in testosterone. A 2024 systematic review of supplements sold as testosterone boosters covered 52 studies published over two decades, 5 of them on zinc or magnesium, and concluded that most of the products fail to raise total testosterone; zinc is not among those it names as effective or possibly effective. None of the sources here tested zinc alone in men with low testosterone and normal zinc status, and apart from the one trial in postmenopausal women the human evidence is in men.

Restricting zinc had the opposite effect. In the same 1996 study, 4 healthy young men who ate a zinc-restricted diet for 20 weeks saw testosterone fall from 39.9 to 10.6 nmol/L. A 2023 systematic review of 38 papers, 8 in people and 30 in animals, concluded that zinc deficiency lowers testosterone and supplementation raises it, and that the size of the effect varies with starting zinc and testosterone levels, the form and dose of zinc, and how long it is taken. It summarised the studies without pooling them into a single estimate.

On zinc status and safety, NIH Office of Dietary Supplements figures put 8.6 percent of US males aged 10 and older below the serum zinc cutoff for their age and sex. The Food and Nutrition Board set the upper intake level for adults at 40 mg a day from food and supplements combined, based on zinc's adverse effect on copper status. The fact sheet notes that this level does not apply to people receiving zinc as medical treatment. The studies that reported a rise used about 30 mg and 50 mg of elemental zinc a day. The US prescribing label for zinc given intravenously as part of hospital feeding lists hypogonadism among the deficiency signs it is intended to prevent, and does not mention testosterone.

At the cellular level, work in human and mouse Leydig cells, the cells in the testes that make testosterone, shows a zinc transporter called ZnT8 moving zinc into the cells' mitochondria when they are stimulated, and testosterone production dropping when ZnT8 is silenced or removed. The work is in cells and mice and did not test supplementation in people.