Zinc: cold duration, lozenge dosing and copper balance
Lozenges started early may shorten colds, but the newest Cochrane review rates the evidence low certainty. Long-term high doses can deplete copper.
Education only, not medical advice. Talk to your clinician before starting a supplement, especially if you are pregnant, take medication or have a condition.
Evidence grade: C (A strong, B good with gaps, C limited or mixed, D early)
The meta-analyses
A 2013 Cochrane review found zinc started within 24 hours of symptoms shortened colds in healthy people [1]. A 2017 meta-analysis of lozenge trials estimated colds were about a third shorter, with no clear difference between zinc acetate and zinc gluconate and no evidence that more than about 100 mg per day added benefit [2].
The 2024 Cochrane update, which excluded zinc combined with other ingredients, rated the evidence low or very low certainty: zinc may not prevent colds, may modestly shorten them, and caused more side effects such as nausea and a bad taste [3]. We grade cold-duration evidence C.
Copper balance and safety
The adult upper limit for zinc is 40 mg per day. Chronic intakes above it can reduce copper absorption and cause copper deficiency, which can lead to anemia and nerve problems [4][5]. Short courses of lozenges during a cold are different from daily high-dose capsules. Intranasal zinc has been linked to loss of smell [4].
Sources
- Singh & Das 2013, Cochrane. doi.org/10.1002/14651858.CD001364.pub4
- Hemilä 2017, JRSM Open. doi.org/10.1177/2054270417694291
- Nault et al. 2024, Cochrane. doi.org/10.1002/14651858.CD014914.pub2
- NIH ODS, Zinc fact sheet. ods.od.nih.gov/factsheets/Zinc-HealthProfessional/
- Hoffman et al. 1988, Gastroenterology. doi.org/10.1016/0016-5085(88)90445-3
DOIs verified against Crossref and official pages checked on 2026-10-15.