INFECTIONS
February 28, 2011

Zinc Shortens Colds

Taking zinc supplements at the first sign of a cold may actually shorten its duration. But it's also possible to over-dose.

Despite years of mixed evidence, a new review of zinc studies done over the past couple of decades shows that zinc supplements may indeed reduce the length of the common cold. Dosing, however, remains a question mark. It is possible (though rare) to overdose with zinc supplements, and even low doses may be bothersome to some people.

People who took zinc within 24 hours of the first symptoms of a cold had significantly shorter colds and less severe symptoms than people who did not take it.

In the new study, the authors looked back at the data of 15 earlier studies which included over 1,300 participants. Most of the studies used zinc therapeutically (to treat a cold), and just a couple of the studies used zinc as a preventative method in children.

After crunching the numbers, the authors found that people who took zinc within 24 hours of the first symptoms of a cold had significantly shorter colds and less severe symptoms than people who did not take it. Additionally, after seven days of having a cold, many more people who took zinc reported that their colds were gone than people who did not take supplements.

For children who took zinc as a preventative measure over a five-month period, their chances of getting a cold at all were reduced. Also, the number of days these children were absent from school and the rate they were prescribed antibiotics was also reduced, compared to kids who did not take the supplements.

Side effects were more common in people who took zinc supplements and included nausea and reporting a bad taste in the mouth.

Doses over 150 mg/day have been linked to adverse effects, so it is important not to take too much zinc (according to the NIH, doses less than 40 mg/day are "likely safe" in most adults).

Why is zinc effective against the common cold in the first place? It seems to interfere with how the cold virus replicates itself, which is why symptoms are less severe and colds don’t last as long.

The authors point out that proper dosing is still unclear, however, and more research will be needed to address the issue. Doses over 150 mg/day have been linked to adverse effects, so it is important not to take too much zinc (according to the NIH, doses less than 40 mg/day are "likely safe" in most adults). Another concern will be in the formulation of the supplements, and whether the zinc is in the right form to allow the body to absorb it most effectively.

These studies were also done in otherwise healthy people, so it’s unclear how zinc will work in people who suffer from asthma or other kinds of chronic illness. While researchers are delving into these questions, if you’re basically healthy, it probably won’t hurt to pop a zinc lozenge or two when you come down with a cold, and see if the remedy works for you.

The study was carried out by a team at Post Graduate Institute of Medical Education and Research in Chandigarh, India, and published in the February 16, 2011 issue of the Cochrane Database of Systematic Reviews.

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