Do Probiotics Work?

As physicians, we're constantly bombarded by questions from the right & left, from in front & from behind, from above & below.  If we're lucky, the questions are very specific & detailed, which makes it easier to answer yes or no.  However, when we're asked to extrapolate from a study of a very specific group to someone who doesn't match the group's demographics, it makes it harder to give an unqualified answer.  And more often than not, we're faced with a superficially easy question that in reality is open to debate.

For instance, do probiotics work?  Shouldn't this be a simple yes or no answer?  Either they do or they don't, right?  Well, it turns out the answer is a qualified maybe.  So let's start with some definitions & qualifications.  For instance, probiotics are live micro-organisms that bring about a health-related benefit when administered in an appropriate dose (think colony forming units).  And in what situation are we looking for benefit:  antibiotic-associated diarrhea? lactose intolerance? colon cancer? cholesterol? blood pressure? irritable bowel syndrome?

It turns out that a systematic review & meta-analysis of 63 randomized controlled trials published yesterday in the Journal of the American Medical Association demonstrated probiotics are associated with a decrease in antibiotic associated diarrhea after following 11,811 individual participants.  Relative risk reduction of 0.58 leads to a number needed to treat (NNT) of just 13.

The good news is that this study is not a fluke but rather part of a trend.  A study published in the British Medical Journal (BMJ) in June 2007 demonstrated that consumption of a probiotic drink could decrease one's risk for antibiotic-associated diarrhea.  Two months later in the same journal, use of probiotics in a randomized controlled trial demonstrated an ability to decrease antibiotic associated diarrhea.  Then earlier this year in February, a quick review in BMJ again suggested that probiotics are a reasonable option in preventing antibiotic associated diarrhea.

So while the trends are all pointing in the same direction, the devil is in the details.  How many colony forming units of which strains, how often, for what purpose?  If you' can't wait for a more definitive study, you'll need to chat with your nutritionist.  And remember to be more specific regarding your questions.

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