Study: Zinc is Not Useful in Colds
By Jorge M. Rivas
Takeaways
A comprehensive review reveals that zinc may not be effective in colds after all. A new study in the journal of Clinical Infectious Disease, reveals that there is no convincing evidence that zinc can actually help fight the common cold.
The review of studies was authored by Thomas J. Caruso and Charles G. Prober, academics at Stanford University Medical School and Jack M. Gwaltney, emeritus professor of internal medicine at the University of Virginia School of Medicine.
The study was prompted to evaluate the evidence behind the purported effects of zinc in the treatment of common colds. This analysis is also timely being that some recent studies report that zinc treatment can be associated with a loss of smell and weakening of the immune system.
To achieve a comprehensive assessment, the authors searched current medical data bases and were able to identify 105 reports published between 1966 and 2006 associated with zinc and colds. Out of these original reports, only fourteen were randomized placebo-controlled trials that evaluated the therapeutic effect of zinc treatments (lozenges, nasal sprays, and gels).
The researchers then rated the quality of each controlled trial based on a set of 11 criteria that assessed the strength of each study. This was done to ascertain if any aspects of the experimental design such as chance, bias or blinding could have affected the significance of the acquired data.
The authors graded facets such as validated case definitions, measurable hypothesis, randomization, doubled blinding, compliance rate, drop out rate, and methods of analysis, among others. They made sure that each of the studies received equal weight for each criterion based on the premise that one of these factors could negate the subsequent clinical findings.
As per the report, the researchers affirmed that only 4 studies met all of the 11 qualifying criteria. Out of these, three investigations did not observe any significant benefits of zinc (lozenges, sprays) therapy on acquired colds. One study utilizing zinc nasal gels did observe a marginal positive benefit. With respect to the other ten studies that were not considered high quality, six observed a benefit with zinc and the other four did not detect any improvements.
The research team also reported that intent-to-treat was the most common criterion that was not met by all of the studies. This is important because it obligates researchers to present data from individuals who did not complete the study. When data from subjects that drop out from a study is not included, it can bias the results in favor of the treatment.
In the Infectious Disease Society of America press release, Dr. Gwaltney stated that "the best scientific evidence available indicates that zinc lozenges are not effective in treating colds."
Sources:
Journal of Clinical Infectious Disease: journals.uchicago.edu
Infectious Disease Society of America:
journals.uchicago.edu
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