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Zinc Supplements: Evidence on Immunity, Testosterone, and Muscle—and What to Watch Out For

Published: 2026-06-24

Written by: Shingo YoshizakiReviewed by: Tomonobu Someda

Do zinc supplements actually work? Can they really raise testosterone?

When zinc is deficient, supplementation has been shown to improve immune function and restore testosterone to normal levels. However, additional supplementation does not raise testosterone in those who are already zinc-sufficient. Checking deficiency status before supplementing is the rational approach.

Zinc's Role: Immunity, Hormones, and Protein Synthesis

Zinc is an essential mineral involved in over 300 enzymatic reactions in the body. It is indispensable for the production and activation of immune cells (T cells, NK cells), synthesis of testosterone and other sex hormones, and protein/DNA synthesis. It also underpins muscle repair and growth. Deficiency presents as reduced immunity, slow wound healing, decreased libido, and fatigue.

300+: enzymatic reactions involving zinc

Effect on Testosterone: Only Effective in Deficient Individuals

In a RCT by Prasad et al. (1996), zinc-deficient older men supplemented with 45 mg/day for 6 months showed approximately a doubling of testosterone—recovering to within normal range. However, RCTs in zinc-sufficient men have not confirmed significant testosterone increases from additional supplementation. In short, 'zinc raises testosterone' is half right—more precisely, 'zinc can restore testosterone to normal levels when deficiency exists.'

~2×: testosterone increase in deficient individuals after supplementation (within normal range)
45 mg/day: dose used in research (6 months)

Evidence for Immune Support

Zinc is required for the production of immune cells including NK cells and T cells, so deficiency reduces resistance to infections. A meta-analysis (Hemilä et al., 2017) showed that zinc lozenges shortened the duration of common colds by an average of 2–3 days, with effects most pronounced when supplementation was started within 24 hours of symptom onset.

2–3 days: reduction in common cold duration with zinc lozenges

Recommended Intake and Precautions: Beware of Copper Antagonism

The recommended daily intake in Japan is 11 mg/day for adult men and 8 mg/day for women. Supplemental doses of 15–30 mg are generally considered appropriate. Long-term supplementation at doses ≥50 mg/day may inhibit copper absorption and cause copper deficiency. High doses can also cause nausea and gastrointestinal symptoms. Zinc gluconate and zinc picolinate are among the more bioavailable forms to look for in supplements.

11 mg/day: recommended zinc intake for adult men (Japan)
≥50 mg/day: threshold above which long-term supplementation may cause copper deficiency