Evidence Trace, complete trial record
In plain terms
In plain terms: Zinc has some human trial evidence supporting it, but the evidence is not yet strong enough for EBL to call it established. It is worth knowing about and worth discussing with your clinician.
Zinc
B
Supported: a good trial, backed by more
The endpoint this grade is based on: self_report, Shorter common colds in adults, using zinc acetate or gluconate lozenges that supply about 75 to 92 mg of zinc a day, started within 24 hours of the first symptoms
The evidence as the record states it
Science et al. (CMAJ, 2012; PMID 22566526): meta-analysis of 17 randomized trials, 2,121 participants; zinc shortened colds by 2.63 days in adults (95% CI 1.58 to 3.69 days) and had no significant effect in children (0.26 days, 95% CI -0.25 to 0.78), with very high heterogeneity. Hemilä et al. (British Journal of Clinical Pharmacology, 2016; PMID 27378206): individual patient data from 3 randomized trials of zinc acetate lozenges, 199 patients; colds 2.73 days shorter. Hemilä and Chalker (BMC Family Practice, 2015; PMID 25888289): the effect comes from lozenges supplying 80 to 92 mg of zinc a day. Hemilä et al. (BMJ Open, 2020; PMID 31980506): a randomized trial of a 13 mg lozenge taken six times a day found no difference in recovery (rate ratio 0.68, 95% CI 0.42 to 1.08), so the dose matters. Grade B on self-reported cold duration in adults, which caps at B. Correcting zinc deficiency is not graded: no cited trial measured a clinical outcome in deficient people, and a rise in blood zinc is a level of the supplement itself.
PMID 22566526 PMID 27378206 PMID 25888289 PMID 31980506
Evidence by specific use
Common-cold duration in adults
Grade B
Science et al. (CMAJ, 2012; PMID 22566526) found colds 2.63 days shorter in adults; Hemilä et al. (Br J Clin Pharmacol, 2016; PMID 27378206) found 2.73 days in individual patient data from 3 lozenge trials; Hemilä and Chalker (BMC Fam Pract, 2015; PMID 25888289) tie the effect to 80 to 92 mg a day; the 13 mg lozenge trial was null (Hemilä et al., BMJ Open, 2020; PMID 31980506). Replicated, on a self-reported endpoint, which caps the letter at B. The Cochrane review this record used to cite was withdrawn in 2015 and no longer supports anything here.
PMID 22566526 PMID 27378206 PMID 25888289 PMID 31980506
Common-cold duration in children
Grade C
Science et al. (CMAJ, 2012; PMID 22566526): in children the pooled effect on cold duration was not significant (0.26 days shorter, 95% CI -0.25 to 0.78). Randomized evidence exists and it is not positive in this group, so the adult result does not transfer: C.
PMID 22566526
Slowing progression to advanced age-related macular degeneration in people at high risk (zinc 80 mg with copper)
Grade C
AREDS (Age-Related Eye Disease Study Research Group, Arch Ophthalmol, 2001; PMID 11594942): 3,640 adults aged 55 to 80 with signs of macular degeneration, followed an average 6.3 years. Against placebo, antioxidants plus zinc lowered the odds of advanced disease (odds ratio 0.72, 99% CI 0.52 to 0.98); zinc alone did not reach the trial's significance level overall (0.75, 0.55 to 1.03) and did once the 1,063 lowest-risk participants were set aside (0.71, 0.52 to 0.99). One trial, positive mainly for the combination and for zinc alone only in the higher-risk subgroup, and not repeated against placebo by an independent group: C. The photographs were graded by masked readers. This does not grade zinc for preventing macular degeneration in people without signs of it.
PMID 11594942
Why Grade B and not Grade A
Grade B reflects moderate human evidence -- typically a single strong trial, multiple smaller trials, or surrogate endpoint data without hard clinical outcome replication. To reach Grade A, Zinc would require at least one additional independent randomized trial demonstrating a hard clinical endpoint or objectively measured functional outcome in a comparable population.
What would move this grade
An independent randomized trial demonstrating a hard clinical endpoint -- mortality, major adverse event, or objectively confirmed functional improvement -- in an adequately powered sample, with results independently replicated, would support Grade A.
Citations withdrawn from this record
PMID 23775705, withdrawn October 2026Singh and Das, Cochrane Database of Systematic Reviews 2013, was withdrawn by Cochrane in 2015 after errors in how its data were derived were raised (the withdrawal notice is indexed on PubMed). A withdrawn review cannot support a grade.
How to track whether this is working
Serum zinc at baseline and 8 weeks: deficiency is common in older adults and the supplementation benefit is most pronounced when correcting a deficit. Also monitor copper levels at 12 weeks if supplementing above 15 mg/day, as zinc and copper compete for absorption. For immune applications, track frequency of upper respiratory infections over a 6-month period.