The findings, reported in the Journal of Allergy and Clinical Immunology, add to a mixed bag of results from research into whether probiotics can help ward off kids' allergies.

Based on what's known so far, it may be that only certain probiotics are helpful for certain kids - but even then, the benefit seems "very modest," according to Dr. Sonia Michail, a pediatric gastroenterologist at Children's Hospital Los Angeles who was not involved in the work.

The 123 kids in this study, which was led by Marie P. Jensen of the University of Western Australia in Perth, were part of a clinical trial as infants, when researchers randomly assigned half to take a probiotic supplement every day for the first six months of life. The rest of the babies were given a placebo.

All of the babies were considered to be at increased risk of allergies because their mothers suffered from them.

In earlier studies, the researchers found no benefits of the probiotic when the babies were 1 to 2.5 years old.

This latest report finds still no effects at the age of 5. Of 66 kids who had received the probiotic in infancy, 44 percent had some type of allergy - such as nasal allergies, food allergies or asthma. That compared with 38 percent of 57 kids who got the placebo.

Probiotics are live microorganisms, usually bacteria, which are naturally present in the gut, and are often added to certain foods, like yogurt and fermented milk, or sold as supplements.

In theory, probiotics given early in life could help curb kids' allergy risk by ensuring a healthy balance of microbes in the intestines, which promotes normal immune function.

Allergies arise when the immune system overreacts to a normally benign substance.

One of the best known and widely used probiotics is Lactobacillus acidophilus - which is what kids in this study were given.

The findings are somewhat surprising, Michail said in an email, because some studies have found that probiotics may help curb certain kids' long-term risk of the allergic skin condition eczema.

But in those studies, the probiotics were different strains of friendly bacteria (L. rhamnosus GG in one study, and a probiotic mix in the other).

And they were given not only to infants, but to their moms starting about a month before delivery, noted Michail, who has researched the role of gut bacteria in kids' health.

What's more, one study found probiotic benefits only among kids who'd been born by C-section.

"Interestingly, the intestine of a baby just born does not have any bacteria, but this quickly changes and the intestine becomes populated by large numbers of bacteria called ‘flora,'" Michail said.

Babies born via C-section are not exposed to their moms' beneficial bacteria in the birth canal, and studies have linked C-section birth to a higher allergy and asthma risk.

The "different bacterial profile" in babies born by C-section "may be permissive to the development of allergies," Michail explained.

But the bottom line is that even in the positive studies, the benefits of probiotics seem small.

In the U.S., the Food and Drug Administration classifies probiotics as a food or dietary supplement. That means the products don't have to be proven effective before hitting the market, but they cannot be promoted for treating or preventing any specific disease.

SOURCE: bit.ly/QZYVSG Journal of Allergy and Clinical Immunology, online September 10, 2012.

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