Stirring Up Helpful Bacteria
Johns Hopkins - Health After 50
It may come as a
shock, but your body is a bacterial condo—home to 10 times as many bacterial cells as human cells. Indeed, about 100
trillion bacterial cells, from more than 500 different species, reside in the human gut, lungs, and skin, while the body itself
contains a mere 10 trillion human cells. What exactly are all of these interlopers up to?
In recent years, scientists have conducted many trials to determine whether people can reap the potential benefits of good bacteria - and thereby dodge or treat various health problems - by consuming specific living microorganisms called probiotics (from the Greek, meaning "for life"). Some early findings are promising. Probiotics appear safe and effective for preventing and treating diarrhea, inflammatory bowel disorders, and fatty liver. Many experts predict that probiotic therapies for these and other illnesses will be available within the next several years.
The beneficial bacteria that normally reside in the gut perform many valuable functions. For instance, they produce substances, such as lactic acid, hydrogen peroxide, and potent antibiotic compounds called bacteriocins, that inhibit the growth of harmful bacteria and fungi. They also compete with disease-causing microbes for nutrients and space, thus hindering overgrowth of the bad bugs. Beneficial organisms also secrete enzymes that aid digestion and produce substances that raise intestinal acidity, thereby promoting the absorption of calcium, magnesium, and zinc.
Finally, many of the benefits of these bacteria appear to stem from their effects on the lymphoid tissue in the gut. According to Jose M. Saavedra, M.D., Associate Professor of Pediatric Gastroenterology at Johns Hopkins, "It is now thought that regular ingestion of probiotic bacteria actually modifies both immune-enhancing and immune-suppressing cells in the gut, which helps modulate the immune response. Thus, probiotics can heighten the body's response to viruses, while decreasing the response to certain antigens, such as those responsible for food allergies."
Probiotics are living microorganisms identical to those that normally reside in the body and exert a positive effect on health when ingested. At present, the best-studied probiotics are Lactobacillus and Bifidobacterium species, which are termed lactic acid bacteria because they use sugar as a food source and generate lactic acid in return. These same microbes convert mile into cheese and yogurt. Other beneficial bacteria include Streptococcus thermophilus and a harmless form of the common intestinal bacterium Escherichia coli. The yeast Saccharomyces boulardii has also produced benefits and is considered a probiotic. In the past few years, scientists have also been investigating the effects of food ingredients called prebiotics, nondigestible carbohydrates that selectively foster the growth of specific organisms already present in the intestine.
Gastrointestinal complaints are likely to be the first disorders addressed with probiotic therapy. Some of the most compelling evidence for the effectiveness of probiotics comes from studies in children with severe diarrhea. Several trials have shown that probiotic therapy can significantly reduce the duration of rotavirus infection, the most common cause of diarrhea in infants and children. (The viruses most likely to cause diarrhea in adults are the Norwalk and Norwalk-like viruses.) And a large multicenter European trial, published in 2000 in the Journal of Pediatric Gastroenterology and Nutrition, showed that adding the probiotic Lactobacillus GG to an oral rehydration solution shortened the duration of severe diarrhea in children.
Probiotics can also help avert episodes of acute viral diarrhea. In a randomized controlled study, Dr. Saavedra and his colleagues at Johns Hopkins found that infant formula supplemented with the probiotics B. bifidum and S. thermophilus helped prevent diarrhea and reduce shedding of rotavirus in hospitalized infants. Probiotic-supplemented infant formulas are widely available in other parts of the world. And the FDA recently paved the way for their introduction into the U.S. by conferring GRAS (generally recognized as safe) status on Bifidobacterium species as an ingredient in such formulas.
According to Dr. Saavedra, "There has also been reasonably convincing evidence that taking a probiotic during antibiotic therapy can help prevent an episode of antibiotic-associated diarrhea." For example, a meta-analysis of nine probiotic trials in the June issue of the British Medical Journal concluded that Lactobacillus strains and S. boulardii appeared to be effective in preventing antibiotic-associated diarrhea. Lactobacillus GG has also provided effective in the treatment of Clostridium difficile infection, which may occur as a result of antibiotic therapy and lead to colitis (inflammation of the lining of the intestine).
Invading microorganisms can increase the permeability of the gut wall, allowing unwanted proteins to enter and cause the intestine to become inflamed. By keeping these invaders in check, probiotic organisms may help preserve the integrity of the gut wall and protect against inflammation - which may, in turn, help prevent or treat inflammatory bowel disorders such as ulcerative colitis and Crohn's disease.
Two controlled trials have found that the probiotic E. coli achieved results comparable to those of mesalamine (Asacol, Pentasa, Rowasa), a standard drug used to treat ulcerative colitis. In addition, a multicenter trial recently reported in Gastroenterology showed the VSL#3, a probiotic that combines three Bifidobacterium species, four Lactobacillus strains, and one Streptococcus strain, helped prevent the patients with ulcerative colitis who have undergone surgical resection of the colon. Probiotics' possible role in managing Crohn's disease is still unclear. Dr. Saavedra notes, "There are no definitive data yet showing that probiotic therapy decreases recurrence or leads to permanent remission in Crohn's disease, but this is an area of active investigation."
Fatty liver is a disorder commonly associated with obesity and diabetes, and recent findings suggest that increased production of ethanol due to the overgrowth of certain intestinal bacteria in obese individuals may contribute to the development of this disorder. In a study in Gastroenterology in April, Johns Hopkins researchers reported that probiotic therapy (with VSL#3) for one month reduced chronic inflammation and fatty infiltration of the liver in obese mice with fatty liver. This finding supports the idea that overgrowth of ethanol-producing bacteria in the intestine may well play a role in fatty liver. A human trial is planned. "If probiotic agents work in humans as well," says lead researcher, Anna Mae Diehl, M.D., Professor of Medicine in the Department of Gastroenterology at Johns Hopkins, "it would be a great therapy for this kind of liver disease. Some of these bacteria are the same as the ones in yogurt, so it's thought to be very safe and should be relatively inexpensive."
A spate of studies have suggested that probiotic therapy may be helpful for disorders unrelated to the gastrointestinal system. For example, there is evidence that probiotics can reduce the rate of respiratory infections in children, enhance immunity in the elderly, protect against cavities, and combat bacterial vaginosis, a common infection of the reproductive tract in women. It may also improve lactose intolerance and reduce food-related allergies.
In many ways, probiotic therapy represents one of the most promising forms of alternative therapy, but several caveats remain. For example, according to Dr. Saavedra, the ingested probiotics do not permanently colonize the gastrointestinal tract. "Once you stop taking the probiotics, the bacteria in the colon return to their previous level." Thus, to maintain their beneficial effects for certain disorders, probiotics would probably have to be taken indefinitely. Fortunately, the strains tested to date appear very safe. "It's virtually impossible to overdose on probiotic bacteria, because we already have trillions of them in our colon."
More research is essential to identify the best probiotic - and the optimal dose - for managing a particular condition. And many experts believe that better regulation of probiotics is needed to ensure that the over-the-counter products now widely available contain viable microorganisms in the amounts stated.
© 2002 Medletter Associates, Inc.
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This information is educational in context and is not to be used to diagnose, treat or cure any disease. Please consult your licensed health care practitioner before using this or any medical information.