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Oral zinc reduces duration of common cold in adults but not children

Clinical Question:
Does oral zinc reduce the duration and severity of the common cold?

Bottom Line:
Oral zinc in a dose of 75 mg or more modestly reduces the duration of symptoms in adults with the common cold, although it also causes nausea and a bad aftertaste. Zinc does not appear to be effective in children, perhaps because of lower doses in pediatric studies, and has minimal impact (if any) on symptom severity. (LOE = 1a)

Reference:
Science M, Johnstone J, Roth DE, Guyatt G, Loeb M. Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials. CMAJ 2012;184(10):e551-61.  [PMID:22566526]

Study Design:
Meta-analysis (randomized controlled trials)

Funding:
Self-funded or unfunded

Setting:
Outpatient (any)

Synopsis:
The Essential Evidence database includes 2 previous POEMs regarding the use of zinc to treat the common cold that are both more than 10 years old; one found no benefit in children (POEM #598), and the other found a modest benefit in adults (POEM #21259).This meta-analysis provides a nice overview of the entire literature. The authors did a careful search for studies that randomized patients with the common cold to receive oral zinc or placebo within 3 days of symptom onset. They did not include intranasal zinc, which has been linked to anosmia. They found 17 studies with 2121 patients, of which 14 provided quanititative data for the quantitative meta-analysis. Studies were of moderate quality. Although all were believed to mask patients and outcome assessors appropriately many did not report information about allocation concealment or generation of the randomization sequence. Overall, patients receiving zinc had 1.65 fewer days of symptoms (95% CI, 0.8 to 2.5 days). There were trends toward lower symptom severity and fewer symptomatic patients at 3 days, and a significant reduction in patients symptomatic at 7 days (relative risk = 0.63; 0.44 to 0.9). Nausea and a bad aftertaste were significantly more common among patients taking zinc, though. The prespecified subgroup analyses found a benefit in 5 studies of adults (2.6 vs 0.26 fewer days of symptoms), but not in the pooled analysis of 3 studies of children. The authors also found a somewhat greater benefit with high-dose zinc (at least 75 mg ionized zinc per day) than with lower dose formulations. Zinc acetate appeared to be more effective than other formulations, although the small number of studies make it difficult to draw firm conclusions.

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