Lactobacillusacidophilus (L. acidophilus) is the most commonly used probiotic, or "good" bacteria. Many healthy bacteria live in the intestines and vagina where they protect against the "bad" bacteria that cause disease. They do this in a couple of ways. For example, when L. acidophilus breaks down food in the intestine, several substances are formed (such as lactic acid and hydrogen peroxide) that create an unfriendly environment for "bad" bacteria. Health practitioners often recommend probiotics as a supplement while taking antibiotics. Antibiotics kill bacteria, but don't discriminate between "friendly" and "unfriendly" organisms. So the balance between good and bad bacteria in the intestines can be upset. Some researchers think that taking probiotics helps restore the healthy balance of bacteria.

Other probiotics include several Lactobacillus species such as L. bulgaricus, L. casei, L. reuteri, Lactobacillus GG, Bifidobacterium longum, Bifidobacterium bifidum, Streptococcus thermophiles, and Saccharaomyces boulardii (a kind of yeast).

In addition to probiotics, some health care providers suggest taking prebiotics. Prebiotics are soluble fiber found in some foods or supplements that help probiotics thrive in the intestine. Examples include fructooligosaccharides (FOS), a carbohydrate found in some fruits and vegetables.

The Food and Drug Administration (FDA) has not approved L. acidophilus for any medical use. However, health practitioners may recommend the supplement for a variety of uses, including the following.

Vaginal infections

Several studies suggest that using L. acidophilus vaginal suppositories can help treat bacterial vaginosis. A small number of clinical studies suggests that eating yogurt with L. acidophilus cultures may also help. Some people also use L. acidophilus to treat or prevent vaginal yeast infections. More research is needed.

Diarrhea prevention

The evidence for using Lactobacillus to prevent diarrhea is mixed. Some research suggests L. acidophilus may be effective when used to prevent traveler's diarrhea (caused by eating contaminated food). Other studies show that Lactobacillus GG was effective. A mix of probiotics (Saccharomyces boulardii and a mixture of L. acidophilus and Bifidobacterium bifidum) helped treat traveler's diarrhea in preliminary studies.

Probiotics, especially Lactobacillus GG, may help prevent or treat infectious diarrhea in children and adults, although the evidence is mixed. Studies seem to show probiotics are most effective in treating rotavirus in children and campylobacter infections in adults. Diarrhea in children can be serious. You should call your doctor if it lasts more than a day or your child seems dehydrated.

Other studies show that taking probiotics regularly may help prevent gastrointestinal infections in adults. In fact, research shows that taking L. acidophilus along with other probiotic strains may enhance immune function and improve overall health. One study found that a 2-strain probiotic, including L. acidophilus, twice a day for 3 months reduced symptoms of the common cold and school absenteeism in school children.

Several studies suggest that probiotics, especially Lactobacillus GG and S. boulardii, may help prevent antibiotic-associated diarrhea. Antibiotic-related diarrhea can be serious, so you should tell your doctor about it.

Other uses

Although evidence in most cases is preliminary or mixed, Lactobacillus and other probiotics have been suggested for a number of remedies and conditions, including:

• Replacing the "friendly" intestinal bacteria destroyed by antibiotics.
• Helping digestion and suppressing disease-causing bacteria.
• Treating chronic constipation.
• Treating symptoms of irritable bowel syndrome (IBS) and inflammatory bowel disease (such as Crohn disease and ulcerative colitis).
• Improving lactose tolerance.
• Enhancing the immune system. Studies suggest that consuming yogurt or milk that contains specific strains of Lactobacillus, or taking supplements with Lactobacillus or Bifidobacterium, may improve the body's natural immune response. One study found that supplementation for 6 months was a safe and effective way to reduce fever, cough, and duration of antibiotic treatment, as well as lessen the number of missed school days for children 3 to 5 years of age.
• Lowering the risk of pollen allergies.
• Reducing the risk of childhood eczema.
• Helping to treat high cholesterol.

The primary dietary sources of L. acidophilus include milk enriched with acidophilus, yogurt containing live L. acidophilus cultures, miso, and tempeh.

Prebiotics are found in breast milk, onions, tomatoes, bananas, honey, barley, garlic, and wheat.

L. acidophilus preparations consist of dried or liquid cultures of living bacteria. These cultures are usually grown in milk, but can sometimes be grown in milk-free cultures. L. acidophilus is available in the following forms:

• Freeze-dried granules
• Freeze-dried powders
• Freeze-dried capsules
• Liquid preparations
• Yogurt enhanced with probiotics
• Vaginal suppositories
• Tablets

Refrigerate L. acidophilus supplements for best quality. Some preparations are in a form that does not break down under normal temperatures and may be convenient for travelers who cannot refrigerate their supplements. Check the package label for storage instructions.

Marketed probiotics are highly variable, with some products containing single microbes, while others comprise multiple distinct microbes. Studies to verify the composition of probiotic formulations have found that discrepancies are common between the stated and actual number of viable organisms in any given product.

Prebiotics occur naturally in foods, however, supplements provide a more concentrated source. Prebiotics are oligosaccharides, chains of sugar units linked together, and include inulin and fructooligosaccharides (FOS). FOS are the most commonly used.

Pediatric

Newborns and infants (0 to 1 year): Always check with your pediatrician before giving dietary supplements to an infant or child. Topical forms are available that may be used for diaper rash. If your infant is taking antibiotics, ask your doctor if a probiotic supplement might be appropriate as well.

Adult

Recommended doses of L. acidophilus vary depending on the health condition being treated. Check the specific dosage recommendations on the product label. The following are guidelines for the most common uses.

• For prevention or treatment of diarrhea: Take 1 to 2 billion colony forming units (CFUs) per day. Some doctors may recommend up to 10 to 15 billion CFUs per day.
• For vaginal infections: Some supplement manufacturers offer a probiotic suppository for vaginal use. Many people recommend inserting regular probiotic capsules vaginally, as well. Oral medications should only be taken orally. Those seeking a vaginal application should look for formulas specifically designed for vaginal use. Many practitioners rely on the oral use of probiotics to treat and prevent vaginal infections without using any sort of vaginal application of probiotics. You should never insert prebiotics vaginally. Speak with your physician.
• For maintaining intestinal health: For healthy adults, take 1 to 15 billion CFUs daily. For the prevention of antibiotic-related diarrhea, some doctors recommend taking L. acidophilus 2 to 3 hours after the antibiotic.

If diarrhea or bloating occurs, reduce the dosage, or stop taking the product, and talk with your doctor.

Because of the potential for side effects and interactions with medications, you should take dietary supplements only under the supervision of a knowledgeable health care provider.

Lactobacillus acidophilus is generally considered safe for most people. Gas, upset stomach, and diarrhea are potential side effects in some people (not on antibiotic therapy) who take more than 1 to 2 billion L. acidophilus CFUs daily.

There has been one report of anaphylaxis (a serious allergic reaction accompanied by shortness of breath and loss of consciousness) in a person taking inulin, a type of prebiotic.

People with weakened immune systems (such as those receiving chemotherapy or drugs that suppress their immune systems) should ask their doctors before taking probiotics.

People with artificial heart valves should not take L. acidophilus because of the rare chance of bacterial infection.

If you are currently being treated with any of the following medications, you should not use Lactobacillus or other probiotics without talking to your health care provider first.

Sulfasalazine: A laboratory study suggests that L. acidophilus speeds up metabolism of sulfasalazine, a medication used to treat ulcerative colitis.

Antibiotics: Antibiotics may kill acidophilus bacteria. Take antibiotics at least 2 hours before or after you take this remedy.

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