Benefits
Immune support, studied as lozenges in adults with common colds
In three small placebo-controlled trials, adults who dissolved a lozenge with about 13 mg zinc as zinc acetate every 2 to 3 waking hours, starting within a day of their first cold symptoms, had colds about 3 days shorter than with placebo. A larger trial of a commercial zinc acetate lozenge taken for 5 days found no faster recovery, and an independent review of zinc trials rated the evidence on shorter colds as low certainty.
Absorption compared with zinc oxide
In a crossover study in 10 healthy adults, a single 50 mg dose of zinc as zinc acetate raised blood zinc more than the same dose as zinc oxide, and the gap was largest when stomach acid was lowered with an acid-reducing drug. Zinc acetate has not been compared directly with zinc gluconate or citrate for absorption in the studies cited here.
Zinc's everyday roles in the body
Zinc is needed for the activity of hundreds of enzymes and plays roles in immune function, protein and DNA synthesis, wound healing and cell division, and it is involved in the sense of taste. These roles apply to zinc from any well-absorbed form. The adult RDA is 11 mg a day for men and 8 mg for women.
Mechanism of action
Lozenge dose and make-up matter
In a review of 13 placebo-controlled lozenge comparisons, the five trials giving under 75 mg zinc a day found no effect on cold length, while higher-dose trials did. A later pooled analysis found colds shortened by 40 percent in three zinc acetate trials and by 28 percent in four zinc gluconate trials, a difference that was not statistically significant.
High doses block copper absorption
Large doses of zinc make intestinal cells produce metallothionein, a protein that binds copper and keeps it from being absorbed. This is why zinc acetate is used as a prescription drug in Wilson disease, a genetic copper-overload disorder, and why long-term high zinc intake can cause copper deficiency in other people.
Clinical trials
Randomized, double-blind, placebo-controlled trial: one lozenge with 13.3 mg zinc as zinc acetate, or placebo, every 2 to 3 waking hours, started within 24 hours of cold symptoms (Prasad et al. 2008, J Infect Dis)
50 adult volunteers with a new common cold.
Colds lasted 4.0 days on average with zinc versus 7.1 days with placebo, with shorter cough (2.1 vs 5.0 days) and nasal discharge (3.0 vs 4.5 days) and lower symptom severity scores. Adverse effects were similar in both groups. This was a small trial.
Randomized, double-blind, placebo-controlled trial of lozenges with 13 mg zinc as zinc acetate, six a day for up to 5 days after a cold began (Hemilä et al. 2020, BMJ Open)
253 working adults in Finland were randomized; the 87 who caught a cold were analyzed.
There was no difference in recovery rate over 10 days (rate ratio 0.68, 95% CI 0.42 to 1.08). In the 2 days after the lozenges were stopped, the zinc group recovered more slowly than placebo. Only 37% of the zinc group reported no adverse effects, versus 69% on placebo.
Individual patient data meta-analysis of three randomized placebo-controlled trials of zinc acetate lozenges in people with colds (Hemilä et al. 2016, Br J Clin Pharmacol)
199 people with common colds, most aged 20 to 50.
Colds were 2.7 to 2.9 days shorter with zinc acetate lozenges, against an average cold length of 7 days in the three trials. The effect did not differ by allergy status, smoking, baseline severity, age, sex or ethnic group. All three trials were small.