This news release describes results of a meta-analysis of seven studies on the use of zinc lozenges for shortening the duration of common colds. The study compared the effectiveness of two kinds of zinc salt in lozenges: zinc acetate and zinc gluconate. Although the studies with zinc acetate lozenges shortened colds more than those with zinc gluconate lozenges, the difference wasn’t large enough to be statistically significant.
Researchers also compared the effectiveness of various doses of zinc in the lozenges and found that five trials that used low doses of 85 to 92 mg per day were just as effective as trials that used 192 to 207 mg per day. The conclusion of the study was that zinc lozenges do shorten the length of the common cold, but more studies are needed to confirm optimal ingredients of lozenges and the ideal dosage.
The news release is meticulous about accuracy in reporting the study findings, but doesn’t provide any information about when zinc should be taken, the actual benefit in terms of days shaved off from suffering cold symptoms, and alternatives and disadvantages of using zinc to treat the common cold.
Zinc lozenges as a means of treatment for the common cold have begun to get widespread public attention in the past three to five years. With colds being an issue that touches many people at least once a year, it is useful for the general public to have information about what type of zinc lozenge could be most effective.
No mention is made in the release about how much zinc lozenges cost. Zinc supplements can be purchased at pharmacies and most supermarkets for less than $10.
The release release gives details from the original study regarding benefits of both types of zinc lozenges, as well as dosages.
But the benefits are only given in relative terms, and not actual numbers. The release would have been improved if it had included the number of days a cold lasts with or without zinc supplements. We’re not sure a 30 percent shorter duration is a meaningful measure, especially without mentioning how long the average cold lasted, with ot without zinc supplementation. Another important consideration is when the zinc was taken. Does it need to be taken continuously as a preventative or does it need to be started immediately at the first sign of symptoms? If you don’t start right away does that affect how well it works?
The release falls short in its description of harms of the recommended treatment. Sucking on zinc lozenges can have a number of minor but unpleasant side effects, like leaving a metallic taste in your mouth, and, less commonly, vomiting, stomach cramps, and diarrhea. The article warns that certain other ingredients in lozenges can cause zinc not to be absorbed. However, it would have been better to spell out that zinc can interfere with the absorption of some classes of antibiotics, making those medications less effective as well.
Strength of evidence in a meta-analysis depends on both the quality of the evaluation of the included studies by the researcher, and the quality of the original studies themselves. This news release explains that the original seven studies were randomized, placebo-controlled clinical trials and gives some information about how the aggregate effectiveness of zinc lozenges was evaluated across studies. It also explains why one of the seven studies was an outlier. We would like to have seen a mention of the total number of people involved in the trials (575). The release also could have provided context about other meta-analyses of zinc supplements that have been performed and their conclusions. For instance this 2012 meta-analysis concluded that while zinc may shorten colds, “large high-quality trials are needed before definitive recommendations for clinical practice can be made.”
There is no disease mongering in the news release. It provides some context about how zinc is believed to work to reduce cold symptoms.
The source of funding for the study is not identified. We’ll rate this not applicable since a meta analysis of already completed trials is not particularly costly and may not have needed outside funding. The study itself noted there was no funding.
Arguably the more important issue is whether the included studies were funded by zinc manufacturers and conducted by researchers with ties to the supplement industry. While it would have been nice to see that information included, we won’t dock the release for the omission.
The release doesn’t mention alternative sources of zinc and alternative treatments for cold symptoms. Zinc is available in a number of common foods — beef, lamb, cashews, and chocolate among others.
The release doesn’t talk about the availability of zinc lozenges, but given that a search on Amazon turns up hundreds of sources, and most grocery and drug stores stock zinc, that’s not a significant omission.
This release release doesn’t claim the use of zinc lozenges to fight the common cold is a novel idea. The language about the purpose of the meta-analysis to determine whether there is a difference in effectiveness between types of zinc salts in lozenges is clear.
The release doesn’t rely on sensational or unjustifiable language. However, it comes close when the study author states that there’s no justification for the popular phrase,”there is no cure for the common cold” because of the strong evidence that zinc lozenges can shorten common cold duration by over 30%.” A 30 percent reduction in cold duration is not necessarily a cure.