The reports arose out of a recent update of a 1999 Cochrane Collaboration review that included trials testing zinc preparations in the treatment or prevention of colds.
Before boosting zinc sales, it’s worth pausing to read this report from the NHS’s excellent Behind the Headlines service, which analyses the science behind media reports.
While many media reports did include at least some mention of the provisos and limitations of the review’s findings, many readers may take away quite a different impression from the NHS analysis than they did from some of the media reports about the review.
The Behind the Headlines analysis notes:
Importantly, the researchers say they cannot recommend taking zinc for colds without further research into what dosage, formulation and duration of treatment will produce benefits with the least risk of side effects (which include bad taste and nausea for zinc lozenges).
For many people, the limited benefit seen here may not seem worth the expense and possible side effects of taking zinc. This is an individual decision. It is possible that zinc will benefit some groups of people more than others, such as those with lowered immune systems. However, it is not clear whether this is the case as the review did not find any studies in these populations.
The Hitting the Headlines analysis also notes that there was a high level of heterogeneity between the studies that were pooled to determine the effect of zinc on the duration of cold symptoms, and that this may suggest that it was inappropriate to pool them: “It certainly makes this particular finding less conclusive.”
The analysis concludes:
More research will undoubtedly be published on this topic. Over time, this can be added to systematic reviews, such as this one. As the evidence grows, it will allow subgroup analyses that can answer outstanding questions about dose and who will benefit most.
Until then, the body of evidence for zinc supplementation seems to be swinging in favour of its benefit, and the choice of whether to take supplements is an individual one.
Many healthy people may not see the potential benefits of taking zinc as being worth the expense of supplements or the possible side effects, which can include nausea. Some preparations don’t taste very good, either. People should stick to recommended daily allowances, which are specified as maximum doses on supplement preparations.