Zinc
Summary
An essential trace mineral; correcting deficiency is its established role. Meta-analyses of lozenge RCTs suggest zinc acetate lozenges started within 24 hours of cold onset may shorten cold duration, but the evidence is debated and depends on dose and formulation.
Mechanism
Zinc is an essential cofactor for hundreds of enzymes and supports immune cell development and barrier function. In the cold literature, zinc ions from lozenges are hypothesized to inhibit rhinovirus binding and replication in the oral and nasal mucosa when exposure begins within the first day of symptoms.
Reported effects
Ratings are relative to peers in the same category, not absolute claims.
Studied dosing: research context
Cold trials used roughly 80-92 mg/day of elemental zinc as zinc acetate lozenges, started within 24 hours of symptom onset and continued during the cold. For comparison, the adult RDA is 11 mg/day for men and 8 mg/day for women. These are doses used in research, not guidance.
Research context only. This is not a recommendation.
Safety
Common side effects at lozenge doses include nausea and bad taste. Chronic high-dose zinc intake depletes copper, which can cause anemia and neurologic effects, so copper status is the interaction most emphasized in the literature. Acute very high doses can impair immune function.
Limitations
Cold trials are heterogeneous in zinc salt (acetate vs gluconate), dose, and timing, which explains much of the disagreement. The Cochrane review history is contentious: an earlier version was withdrawn in 2015 after errors were identified. No consistent benefit has been shown for cold prevention in the general population.