February 18, 2011 — When given within 24 hours of onset of symptoms, zinc reduces the duration and severity of the common cold in healthy people, according to the results of a Cochrane systematic review reported online February 16 in the Cochrane Database of Systematic Reviews.
"This review strengthens the evidence for zinc as a treatment for the common cold," said lead author Dr. Meenu Singh, from the Post Graduate Institute of Medical Education and Research in Chandigarh, India, in a news release. "However, at the moment, it is still difficult to make a general recommendation, because we do not know very much about the optimum dose, formulation or length of treatment."
To evaluate the effect of zinc on common cold symptoms, the reviewers searched CENTRAL (2010, Issue 2), which contains the Acute Respiratory Infections Group's Specialised Register, MEDLINE (1966 to May week 3, 2010), and EMBASE (1974 to June 2010). Inclusion criteria were randomized, double-blind, placebo-controlled trials in which zinc was used for 5 or more consecutive days to treat the common cold, or for 5 or months or longer for prevention. Data were independently extracted and trial quality examined by 2 reviewers.
The search identified 13 therapeutic trials enrolling a total of 966 participants, and 2 preventive trials enrolling a total of 394 participants, that met selection criteria. Zinc intake was associated with a significant decrease in duration of common cold symptoms (standardized mean difference [SMD], −0.97; 95% confidence interval [CI], −1.56 to −0.38; P = .001), as well as in severity (SMD, −0.39; 95% CI, −0.77 to −0.02; P = .04).
The proportion of participants symptomatic after 7 days of treatment was lower in the zinc group vs the control group (odds ratio [OR], 0.45; 95% CI, 0.2 - 1.00; P = .05). The zinc group also fared better than the control group in incidence rate ratio (IRR) for development of a cold (IRR, 0.64; 95% CI, 0.47 - 0.88; P = .006), school absence (P = .0003), and prescription of antibiotics (P < .00001).
However, overall adverse events were higher in the zinc group (OR, 1.59; 95% CI, 0.97 - 2.58; P = .06), as were bad taste (OR, 2.64; 95% CI, 1.91 - 3.64; P < .00001) and nausea (OR, 2.15; 95% CI, 1.44 - 3.23; P = .002).
"Our review only looked at zinc supplementation in healthy people," Dr. Singh said. "But it would be interesting to find out whether zinc supplementation could help asthmatics, whose asthma symptoms tend to get worse when they catch a cold."
Limitations of this review also include those inherent in the individual studies, such as placebo-blinding adequately described in only 6 trials, and allocation concealment unclear in 5 studies.
"[U]nlike trials relying on experimentally-induced rhinoviral colds, findings from large community-based trials will address issues relating to the diversity of and generalisability to the common cold," the review authors conclude. "In addition, given its toxicological profile, the potential for zinc to induce adverse effects at the doses participants are required to take also needs to be determined."
The study authors have disclosed no relevant financial relationships.
Cochrane Database Syst Rev. Published online February 16, 2011. Abstract
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