Zinc benefits: what the research does and doesn't show

The evidence doesn't support zinc as a treatment for the common cold, low testosterone, hair loss, or any skin condition. The two questions with actual randomized-trial data behind them are cold-lozenge duration and testosterone in men who were already marginally zinc-deficient — and neither generalizes to taking a standard multivitamin-level zinc dose while otherwise healthy.

What the evidence doesn't support

Zinc's basic biology is well established: it's a cofactor for hundreds of enzymes and is needed for normal immune cell development, DNA and protein synthesis, and taste and smell, according to NIH's Office of Dietary Supplements. That's textbook nutrition science, not a clinical trial result, and it's a different claim from "taking more zinc improves any of those systems in someone who already gets enough." The trials below don't support zinc lozenges or capsules as a treatment for an active cold beyond shortening its length by about a day, don't support extra zinc raising testosterone in a man whose zinc status is already normal, and don't support oral zinc supplementation for hair regrowth, acne, warts, or wound healing in the general population — no randomized trial of typical oral zinc doses for any of those outcomes turned up in the search behind this page. Zinc's role in blood sugar is covered on its own page rather than repeated here: see blood sugar supplements: what the evidence supports.

What the trials found

A 2013 Cochrane review pooled 16 therapeutic trials (1,387 participants) that gave zinc, in some form, within 24 hours of a cold starting. Zinc shortened the duration of cold symptoms by just over a day on average (mean difference -1.03 days) but didn't significantly reduce how severe the symptoms felt. The result came with real caveats: heterogeneity across the 16 trials was very high (I² = 89%), and side effects — mainly a bad taste and nausea — were significantly more common in the zinc groups. The review's own authors put a number on the dose that actually worked: lozenges delivering 75 mg of zinc or more per day throughout the cold.

A more focused 2017 meta-analysis by the same lead researcher looked at seven placebo-controlled lozenge trials (575 participants) and compared zinc acetate against zinc gluconate lozenges. Colds were about a third shorter with zinc overall (33%, 95% CI 21-45%) — 40% shorter with acetate, 28% shorter with gluconate, a difference the analysis said wasn't statistically significant. Trials using 80-92 mg/day and trials using 192-207 mg/day found essentially the same benefit, so there was no sign that a higher dose worked better. Both of those numbers are worth sitting with: 75-207 mg/day, taken as lozenges for the several days a cold lasts, is far above a typical zinc supplement (8-40 mg/day) and well above the adult tolerable upper intake level of 40 mg/day for ongoing daily use. This is short-term, symptomatic use studied at a specific high dose in lozenge form — not a case for taking more zinc every day.

On testosterone, the trial most often cited is a small 1996 study that measured cellular zinc and serum testosterone in 40 healthy men aged 20 to 80. In four young men whose dietary zinc was restricted for 20 weeks, testosterone fell from about 40 nmol/L to about 11 nmol/L. In nine elderly men who started out marginally zinc-deficient, 3 to 6 months of zinc gluconate supplementation (about 30 mg/day of elemental zinc) raised testosterone from about 8 nmol/L to about 16 nmol/L. That's a real effect, in a real study — in men who were deficient to begin with. Nothing in this trial, or any other identified for this page, tested whether extra zinc raises testosterone in a man whose zinc status is already normal, and a sample of nine or four people is too small to generalize from either way.

Question	Strongest trial found	Dose studied	What it doesn't tell you
Common cold duration	Cochrane review, 16 trials, 1,387 people	Lozenges, ≥75 mg/day, taken during the cold	Doesn't apply to typical daily supplement doses or forms other than lozenges
Testosterone	Prasad et al. 1996, 4-9 men per group	~30 mg/day elemental, 3-6 months	Only tested in men who were already marginally zinc-deficient
Hair, skin, warts, wound healing	No randomized trial of oral zinc found	Not established	Topical zinc oxide (sunscreen, diaper cream) is a different product and question

Questions people ask

Is zinc good for a cold? Can zinc help with a cold?

The best evidence on this — a 2013 Cochrane review of 16 trials — found zinc lozenges taken within 24 hours of a cold starting shortened its duration by about a day, but only at doses of 75 mg or more per day and with more reported nausea and bad taste than placebo. It didn't reduce how bad the symptoms felt. That's a specific, short-term, high-dose use case, not evidence for taking zinc daily to avoid getting sick.

How much zinc should I take when sick?

The trials that found a benefit used zinc lozenges at 75-207 mg per day, taken only for the several days a cold lasted — well above the 40 mg/day adult upper intake level for ongoing use. This page doesn't recommend a dose for treating a cold; that's a conversation for a doctor or pharmacist, especially since the same trials found more nausea and bad taste at those doses.

Does zinc increase testosterone? Can zinc boost testosterone?

Only in men who were already marginally zinc-deficient, in one small 1996 study of fewer than ten men per group. There's no trial showing that extra zinc raises testosterone above normal in a man whose zinc status is already adequate.

Is zinc good for hair growth or hair loss?

No randomized trial of oral zinc supplementation for hair regrowth in the general population turned up in the search behind this page. Zinc deficiency is a recognized, uncommon cause of hair thinning, which is a different question from whether extra zinc helps hair in someone who isn't deficient.

Is zinc oxide good for skin?

That's a different product and a different question from an oral zinc supplement. Topical zinc oxide is a long-established, FDA-recognized skin protectant and sunscreen active ingredient — its use on skin isn't the subject of the oral-supplement research reviewed on this page.

What is zinc good for? What does zinc do for the body?

As a nutrient, zinc is required for hundreds of enzyme reactions, immune cell development, and DNA and protein synthesis — that's established nutrition science, not a supplement claim. What's not established is that taking more of it than your diet already provides improves any of that in someone who isn't deficient. The two outcomes with actual randomized-trial data are covered above: cold duration at high lozenge doses, and testosterone in men who started out deficient.

Is zinc good for you?

Zinc is an essential nutrient — everyone needs it, and a genuine deficiency causes real problems. "Good for you" as a general claim isn't really a testable question, though; the specific things researchers have actually measured are covered above, and most of what zinc is marketed for hasn't been tested the way the cold and testosterone questions have.

When to talk to a doctor

Frequent infections, unusual fatigue, or symptoms that might suggest low testosterone are worth raising with a doctor, who can test zinc and testosterone status directly rather than guessing from a supplement label. Zinc is not a treatment for the common cold, low testosterone, or any diagnosed condition, and nothing in the evidence above supports using it as a substitute for medical evaluation. If you take prescription medication or are pregnant or nursing, talk to a doctor before adding any supplement.

Related reading: what is zinc, how much zinc should you take a day, how to choose a good zinc, and blood sugar supplements: what the evidence supports.