Mike the Mad Biologist

Zinc: Good for Colds?

Erm, maybe not so much. From Clinical Infectious Diseases:

BACKGROUND: Over the past 20 years, the use of zinc as an over-the-counter alternative therapy for the common cold has vastly grown in popularity. Recent reports of potentially permanent anosmia caused by intranasal zinc therapy warrant careful analysis of the therapeutic effects of zinc.

METHODS: A search of the Medline database (including articles published during 1966-2006) for studies of zinc and the common cold produced 105 published reports. Fourteen were randomized, placebo-controlled studies that examined the effect of zinc lozenges, nasal sprays, or nasal gels on naturally acquired common colds. Eleven features of experimental design affecting signal quality, chance, bias, and blinding were used to evaluate the 14 placebo-controlled studies. These criteria were validated case definition, quantifiable hypothesis, sample size calculation, randomized assignment, double blinding, proof of blinding, measurement of compliance, measurement of dropout rate, analysis by intent to treat, description of methods of analysis, and measurements of probability. Equal weight was given to each criterion, because failure to meet any one could potentially invalidate the findings of a clinical trial.

RESULTS: Four studies met all 11 criteria. Three of these studies reported no therapeutic effect from zinc lozenge or nasal spray. One study reported positive results from zinc nasal gel. Of the remaining 10 studies, 6 reported a positive effect and 4 reported no effect. Intent-to-treat analysis was the most common criterion not met.

CONCLUSIONS:
This structured review suggests that the therapeutic effectiveness of zinc lozenges has yet to be established. One well-designed study did report a positive effect of zinc nasal gel.

I’m all for the placebo effect–I ‘rely’ on it regularly to prevent colds. But I had no idea that anosmia could result.

Comments

  1. #1 CRM-114
    August 14, 2007

    Perhaps the one positive effect was due to the gel and not the zinc. I could see where adding moisture, or artificial snot, might improve resistance to colds.

  2. #2 Mike Haubrich, FCD
    August 14, 2007

    In all of the time I was taking extra zinc, and recommending it, I was relying on a popular press version of the results of a study at Johns Hopkins University that showed it is effective and shortening the duration of colds; but not the symptoms. The theory was that it prevented viruses from incubating as it shored up squamous epithelium. So it worked for me, even as a placebo. My colds used to be long-lasting, but now their durations have been roughly half.

    We’ll see now what happens this fall. If my colds go back to being week-long miserable affairs, I will know who to blame.

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