Monday, February 21, 2011

Cochrane review concludes: Zinc works for the common cold?

The Cochrane Collaboration recently published the abstract of a  meta-analysis on zinc for treating the common cold. I cannot get a hold of the entire article, but the brief results are that they found 15 studies that were of suitable quality (randomized, placebo controlled, etc.) with results from 966 participants. They pooled the results and found that, compared to placebo, zinc appeared to reduce the duration of symptoms of the commond cold by about one day.

The zinc had to be started within 24 hours of symptoms starting and the dose, formulation, and duration were not standardized. Statistically, the result was significant (p = 0.001). Also significant was the increase in nausea (115% higher with zinc), bad taste (164% higher with zinc), and overall adverse effect (59% higher with zinc).

1. Zinc might reduce the duration of symptoms of a cold by about one day
2. Equally likely is that you will be nauseated or have other side effects from the zinc
3. We do not know whether to take pills, lozenges, or some other form
4. We do not know what dose or duration is effective

Having conducted meta-analyses of my own, I know that the analyses can be fraught with problems. Now, I do not have any reason to expect that to be the case, and just because a method can be shoddy does not at all imply that it must be, however, the abstract simply does not provide adequate information to give a more thorough analysis of the quality and likely accuracy of the statistical methods.

Should you take zinc? It seems to me that, at best, based on this data, the results are a wash. If we trust the results, is one day less of runny nose and cough worth a week of feeling nauseated from taking pills?

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