What Matters

Preventing the common cold


Throughout history, medicine has a habit of seeking out and holding up to scrutiny various panaceas. Vitamin D had its moment in the sun a few years ago. Now probiotics are perhaps enjoying theirs.

If your practice is like mine, daylight is frequently consumed by chronicity, intractability, and preauthorization forms. One may find it enjoyable to occasionally see a member of the "walking well" with a simple problem – opening the exam room door to spend a few minutes proffering advice to enhance health and prevent disease.

Entertaining the idea of recommending probiotics to prevent the common cold is attractive and energizing, especially because probiotics do not require a prescription or a preauthorization.

So, what’s the evidence?

En-Jin Kang and colleagues at Hallym University College of Medicine in Seoul, South Korea, conducted a systematic review of randomized trials evaluating probiotic administration for reducing the incidence of colds and cold symptoms. Studies were excluded if they focused on sinusitis, tonsillitis, laryngitis, otitis media, and lower respiratory tract diseases such as bronchitis or pneumonia (Korean J. Fam. Med. 2013;34:2-10).

Seven randomized, controlled trials were selected and included in the final analysis. The quality of the studies was high overall, and the researchers detected no tendency for only positive studies to be published.

The relative risk of developing a cold or cold symptoms was 0.82 (95% CI: 0.70-0.97) when probiotics were administered for less than 3 months. But the relative risk rose to 1.0 (95% CI: 0.92-1.09) if administration was longer than 3 months.

When probiotics were administered with vitamins and minerals, the relative risk was 0.87 (95% CI: 0.78-0.97), though it climbed to 0.97 when the researchers discarded two studies that may not have used placebo.

One of the difficulties with this type of meta-analysis may be the heterogeneity of the types of bacteria in the probiotics administered in the different studies. Lactobacillus and Bifidobacterium were the most commonly used genera.

But remember that cold symptoms result from our response to an offending virus, so the type of bacteria in the probiotic may not be relevant. Why not? Some experts have theorized that probiotics may be effective because they reduce our body’s overall inflammatory response.

Except in the relatively rare circumstances of immunocompromised hosts, probiotics are safe. The biggest downside for patients may be cost. But with U.S. patients spending $34 billion per year on alternative therapies, they likely won’t mind the cost – as long as there is at least some evidence they could avoid a cold.

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