We take vitamins and minerals to safeguard our health. Should we also add a daily dose of bacteria?
Bacteria have a reputation for causing disease, so the idea of tossing down a few billion a day for your health might seem — literally and figuratively — hard to swallow. But a growing body of scientific evidence suggests that you can treat and even prevent some illnesses with foods and supplements containing certain kinds of live bacteria. Northern Europeans consume a lot of these beneficial microorganisms, called probiotics (from pro and biota, meaning “for life”), because of their tradition of eating foods fermented with bacteria, such as yogurt. In fact, probiotic-laced beverages are big business in Japan as well as in Europe.
Enthusiasm for such foods has lagged in the United States, but interest in probiotic supplements is on the rise. Some digestive disease specialists are recommending them for disorders that frustrate conventional medicine, such as irritable bowel syndrome.
As often happens with products marketed as being “natural,” some of the purported benefits — from treating acne to preventing cancer and heart disease — are exaggerated. But that doesn’t mean probiotic therapy is without merit. Since the mid-1990s, clinical studies have established that it can help treat several gastrointestinal ills, delay the development of allergies in children, and treat and prevent vaginal and urinary infections in women.
Rationale for probiotics
Self-dosing with bacteria isn’t as outlandish as it might seem. An estimated 100 trillion microorganisms representing more than 500 different species inhabit every normal, healthy bowel. These microorganisms (or microflora) generally don’t make us sick; most are helpful. Gut-dwelling bacteria keep pathogens (harmful microorganisms) in check, aid digestion and nutrient absorption, and contribute to immune function.
If they become depleted — usually because of disease, stress, poor diet, or certain medications — health problems can result. Pathogens may get a foothold, causing diarrhea and sometimes colitis (inflammation of the intestinal lining). The gut wall may become “leaky,” letting through proteins that set off an inflammatory response. That’s why it makes some sense to replenish the bacteria supply or stock up during challenges, such as a round of antibiotics that kills off useful microorganisms along with harmful ones.
The strains most often found in probiotic supplements and foods like yogurt are lactic acid bacteria belonging to the genera Lactobacillus and Bifidobacterium. Commonly used species include L. acidophilus, L. brevis, L. bulgaricus, L. reuteri, L. plantarum, L. rhamnosus, L. salivarius, L. casei, B. bifidum, B. lactis, B. longum, and B. infantis. There are also strains from the Escherichia, Enterococcus, Clostridium, Streptococcus, and Saccharomyces (a yeast) families.
Not all of these bacteria have been researched thoroughly. Most studies have been small, the methodologies imperfect, and the results inconsistent. Preparations and doses have varied. Also, different strains have different health effects, so the findings on one probiotic don’t necessarily apply to others.
The probiotic with the most research behind it is Lactobacillus GG, also known as L. rhamnosus GG (named after its discoverers, Drs. Sherwood Gorbach and Barry Goldin at Tufts University). It has shown good results in treating diarrhea in children and preventing infant allergy.
Some products contain several bacterial strains. For example, VSL #3 is a mix of four strains of Lactobacilli, three strains of Bifidobacteria, and one strain of Streptococcus salivarius. A probiotic preparation may also contain inulin or fructo-oligosaccharides (FOS), plant-based components that certain microflora feed on. Such substances are referred to as “prebiotics.”
Good for some intestinal problems
The best case for probiotic therapy has been in the treatment of diarrhea. It may also help people with Crohn’s disease and irritable bowel syndrome. Because these disorders are so frustrating to treat, many people are giving probiotics a try before all the evidence is in for the particular strains they’re using. More research is needed to find out which strains work best for what conditions.
Acute diarrhea. Controlled trials have shown that Lactobacillus GG can shorten the course of infectious diarrhea in infants and children (but not adults). Other probiotics found effective in children or adults in at least one trial include L. reuteri, L. casei, combination L. acidophilus and L. bifidus, and Bifictobacterium lactis. One study found that B. bifidum and Streptococcus thermophilus added to infant formula reduced the incidence of diarrhea by 24%.
Necrotizing enterocolitis. Probiotics also reduce the risk of necrotizing enterocolitis (NEC), a condition of unknown cause that occurs in very low-birthweight babies and results in intestinal inflammation, tissue damage, and sometimes death. A study in the January 2005 Pediatrics showed that newborns who received L. acidophilus and B. infantis in addition to breast milk had a 63% lower rate of NEC than those who received breast milk alone.
Antibiotic-associated diarrhea. Although studies are limited and data are inconsistent, two large reviews, taken together, suggest that probiotics reduce antibiotic-associated diarrhea by 60%, when compared with a placebo. Some useful strains are Lactobacillus GG, L. plantarum, and Saccharomyces boulardii.
Inflammatory bowel disease. Clinical trial results are mixed, but several small studies suggest that certain probiotics may help maintain remission of ulcerative colitis and prevent relapse of Crohn’s disease and the recurrence of pouchitis (a complication of surgery to treat ulcerative colitis). The evidence, though limited, is strongest for E. coli Nissle 1917 (a specific strain), VSL #3, and Saccharomyces boulardii.
Lactose intolerance. Some people suffer from gas, bloating, and diarrhea if they drink milk because their bodies are short on lactase, an enzyme needed to break down lactose (milk sugar). More than 20 years ago, researchers reported in the New England Journal of Medicine that lactose-intolerant individuals had fewer symptoms if they ate yogurt instead of milk. The bacteria in yogurt produce lactase, which digests the lactose before it reaches the large intestine.
Other gastrointestinal problems. Probiotics are also being studied for treating constipation, traveler’s diarrhea, and H. pylori infection, which causes stomach ulcers and gastric cancer. No strains have been found to be entirely effective in treating irritable bowel syndrome, although some, such as L. plantarum and B. infantis, help relieve individual symptoms such as bloating, gas, or diarrhea.
Possible use in urogenital health
Like the intestinal tract, the vagina is a finely balanced ecosystem. The dominant Lactobacilli strains normally make it too acidic for harmful microorganisms to survive. But the system can be thrown out of balance by a number of factors, including antibiotics, spermicides, and birth control pills. The vaginal and urinary tracts are also at risk because they are so close to the anus, a source of E. coli and other bacteria that should remain confined to the intestinal tract. Probiotic treatment that restores the balance of microflora may be helpful for such common female urogenital problems as bacterial vaginosis, yeast infection, and urinary tract infection.
Many women eat yogurt or insert it into the vagina to treat recurring yeast infections, a “folk” remedy for which medical science offers limited support. Oral and vaginal administration of Lactobacilli may help in the treatment of bacterial vaginosis, although there isn’t enough evidence yet to recommend it over conventional approaches. (Vaginosis must be treated because it creates a risk for pregnancy-related complications and pelvic inflammatory disease.) Probiotic treatment of urinary tract infections is under study.
Recommended doses of probiotics range from 1 billion to 10 billion colony-forming units (CFU) — the amount contained in a capsule or two — several days per week. Lactobacillus GG, marketed as Culturelle, is sold in capsule form. VSL #3 comes in packets of powder that you sprinkle on food. To get the benefits of probiotics in yogurt and other cultured products, make sure the label indicates the presence of “live” or “active” cultures.
There’s not much data on how long you should take probiotics for acute conditions such as infectious or antibiotic-related diarrhea. A daily supplement for one to two weeks is often recommended. Some people take probiotics as a routine prevention measure. Laboratory research and some human studies suggest that probiotics enhance immune function, but more research will be needed before we know if this implies a general health benefit.
Probiotic supplements must be handled and stored properly, because they need to be alive when you take them (or when they’re freeze-dried for capsules). They may die on exposure to heat, moisture, or air. Some require refrigeration. ConsumerLab.com, an independent testing group, found that 8 out of 25 products they checked contained less than 1% of either the number of live bacteria claimed on the label or the minimum one billion CFU.
Some bacteria succumb to stomach and bile acids before they reach the intestine. Others, such as Lactobacillus GG and L. plantarum 299v (a particular strain) have been shown to survive, grow, and adhere to the intestinal wall. Researchers are working on ways to better deliver probiotics to the intestine, such as encapsulating them in protective substances. Some probiotics are enteric-coated.
Are they safe?
Probiotics are generally considered safe — they’re already present in a normal digestive system — although there’s a theoretical risk for people with impaired immune function. Be sure the ingredients are clearly marked on the label and familiar to you or your health provider. There’s no way to judge the safety of unidentified mixtures.
In the United States, most probiotics are sold as dietary supplements, which do not undergo the testing and approval process that drugs do. Manufacturers are responsible for making sure they’re safe before they’re marketed and that any claims made on the label are true. But there’s no guarantee that the types of bacteria listed on a label are effective for the condition you’re taking them for. Health benefits are strain-specific, and not all strains are necessarily useful, so you may want to consult a practitioner familiar with probiotics to discuss your options. As always, let your primary care provider know what you’re doing.
Published: March 9, 2014. By Harvard Health Publications
© 2010 – 2015 Harvard University