DEAR DOCTOR: Doctor: Can you explain probiotics? Who should take them, and are they harmful in any way? They seem helpful to me in calming my stomach.
DEAR READER: For many generations, society feared bacteria, seeing only the devastation that bacterial disease created. Today, with the advent of antibiotics, we have been able to cure infections that once led to illness and death. However, our primary tool -- drugs known as antibiotics -- also indiscriminately kill bacteria that don't cause disease. Only recently have we come to realize how important these non-dangerous microorganisms are to our health. With an estimated 40 trillion bacteria in and on the human body, outnumbering the 30 trillion to 37 trillion cells that make up the body, it's clear that a symbiotic relationship with these organisms is important to our health.
To answer your question about probiotics, first let us look at gastrointestinal bacteria. Many probiotic preparations promise to help replenish beneficial bacteria in the colon, with the theory being that they increase the health of the intestinal lining, suppress inflammation caused by damaging bacteria, and reduce inflammation caused by an overactive immune system. Most probiotics contain species of the familiar bacterial strains known as Lactobacillus and Bifidobacterium, but some preparations also contain beneficial strains of Streptococcus and Clostridium, or even yeast (Saccharomyces boulardii).
In a 2008 study of 224 children with a diarrheal illness related to rotavirus, participants took either a probiotic preparation (containing various strains of Lactobacillis, Bifidobacterium and Streptococcus) or a placebo. On the second and third days of the illness, the group that took the probiotic had a decrease in stool frequency, improved stool consistency and less need for either oral or intravenous rehydration. A 2002 analysis of nine studies that used Lactobacillus for childhood diarrheal illness found an average reduction of illness of 0.7 days in children who took the probiotic.
A 2010 review of 63 studies assessed the impact of different probiotics on acute diarrheal illness; 56 of these studies looked only at children and infants. On average, probiotics decreased the duration of diarrhea by 24 hours and decreased stool frequency by the second day. Although the authors could definitely say there was benefit in children, they could not conclude if these benefits occurred in adults.
As for more chronic illnesses, a 2009 analysis of 16 studies of people with irritable bowel syndrome found that two studies using Bifidobacterium infantis showed a decrease in abdominal pain, bloating and bowel movements. The other studies were considered methodologically flawed, so the authors couldn't assess the probiotics' benefits.
Probiotics have had mixed results in Crohn's disease, but have shown benefit among people with mild to moderate ulcerative colitis, again through the probiotic preparation.
Similarly, some studies have found benefit from probiotics given with antibiotics, which kill the "good" bacteria as well as the "bad" and therefore increase the risk of Clostridium difficile infection. Not all studies show such benefit, but I would consider probiotics if you've developed diarrhea in the past when taking antibiotics.
One potential issue with probiotics is that, unlike medications, they're not regulated, so there is no true way to know exactly what you're getting. Some patients do develop bloating with probiotics, but for the most part the preparations are well-tolerated. If they're helping you, it seems prudent to continue using your current brand.
(Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.)
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