Field of Science

Zinc still doesn't work very well for colds


Cold cure manufacturers continue to push zinc as a cure, despite the lack of evidence.  Today, the Washington Post reported, not for the first time, that taking zinc will shorten the duration a cold by three days in adults.  Sounds pretty good!  Only it's wrong.

The Post reporter apparently didn't really get past the abstract for the new study, which isn't actually a study at all, but just a review of 17 other studies.  The review appeared on May 8 in the Canadian Medical Association Journal.

ALL of the studies were funded by the companies that make zinc supplements, mostly large pharmaceutical companies.  (Big Pharma or Big Supp, they are often the same companies.)  Here's a partial list of the sponsors: Warner Lambert, McNeil Consumer Products, Weider Nutrition, Truett Laboratories, Bristol Myers, Berko Ilac, and Quigley.  Not that there's anything wrong with that!

One problem with the Washington Post summary is that the benefit wasn't really three days, even if you believe the results.  Although the study looked at 17 trials, the core analysis only used eight of them, all of which used patients with naturally acquired colds.  The average benefit was 1.6 days, not 3 days, and it was highly variable.  Reuters and Fox reported the story more accurately as "one and a half days" and pointed out that the effect was just over two and a half days in adults.

Somehow, though, the benefit disappeared in children.  Could this be because children don't care so much about telling the investigators what they want to hear?

And what about those trials that didn't use naturally occurring colds.  As I pointed out in a recent blog post, if you look at only the studies where the researchers intentionally gave people a cold, the effect vanishes.
"The more rigorously scientific studies, where you took a group of people and gave half of them zinc and half a placebo and inoculated their nose with a cold virus, found there were no differences," said Terence Davidson, director of the UC San Diego Nasal Dysfunction Clinic in a February interview.
None of this stops ProPhase (NasdaqGM: PRPH), maker of ColdEeze zinc products, from making this claim on their website:
"Cold-EEZE® has been clinically proven to shorten the duration of the common cold by nearly half."  
As evidence, their website points to three studies from 10-20 years ago.  They conveniently ignore the more recent studies that showed far less (possibly no) benefit.

The authors of the latest review article graded the quality of evidence for five different outcomes.  Their report card on these studies has one "Moderate" and four "Low" grades.  Moderate means "further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.  Most of the grades were "low," which means
"further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate."  
So the authors themselves don't really trust their own study!  In the end, they conclude that "there is only a weak rationale" to recommend zinc.  And previous studies, not funded by supplement manufacturers, showed no benefit.  Who are you going to believe?

Save your money and use it to buy chicken soup instead.*

*The author receives no financial backing from the makers of chicken soup, although he does like it and would appreciate a free sample.

2 comments:

  1. I don't think the difference in the effect of zinc on children is dispositive of results showing zinc is effective. The immune system of a child may differ greatly from that of an adult.

    ReplyDelete
  2. @Anonymous

    Evidence? Children may have a more robust immune system, but how is this connected to them NOT having shorter duration of a cold?

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    It has got to where I am avoiding chain pharmacies in favor of small HMO connected outlets just to avoid this type of product being in my face at the checkout. Once this stuff finds a way to credit itself with dubious studies, the marketers take over. It is all too sad that the media help them out.

    ReplyDelete

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