April 25, 2008  -- Exposing pregnant mothers and infants to probiotic bacteria could help stimulate the growth of the immune system and potentially play a role in preventing allergies, say researchers.

Probiotic bacteria are living micro-organisms that can be used to restore the ecosystem of the gut after a dose of antibiotics, or to help create a stable gut flora that is less prone to diseases like gastroenteritis.

There have also been suggestions that probiotics help prevent the development of allergies, but how they might do this has been a matter of debate.

Now, a Finnish team of researchers led by Emma Marschan at the University of Helsinki has investigated the subject, by treating pregnant women with either probiotics, or a placebo.

Allergic Tendency

The team selected 1223 women who either had a history of allergies, or their partner did, or both. Since susceptibility to allergy is partly genetic, this allowed the team to assume that the babies were "predisposed" to allergies.

The women took probiotic or placebo doses daily from the eighth month of pregnancy. While some women dropped out or did not successfully deliver, 925 infants continued in the study and had the same probiotic or placebo dosage given to them daily for six months after birth.

At three, six, and 24 months, paediatricians examined the children without knowing whether they were probiotic- or placebo-treated babies, and recorded any diagnosis of allergy. In 98 randomly selected infants at six months, blood samples were also collected.

Too Few Bugs?

Marschan and colleagues found that levels of key proteins associated with tissue inflammation were 50% higher on average in the blood of probiotic-treated infants than in the blood of placebo-treated infants. Inflammation is thought to stimulate the immune system, and so reduce allergic reaction.

Probiotic children were also 30% less likely than their untreated counterparts to develop an itchy skin condition known as atopic eczema, which is often an early manifestation of allergies.

"It seems clear that we need to stimulate the infant's immune system as early and as vigorously as is safe, for inflammation seems to go hand in hand with allergy prevention," says Errki Savilahti, an author of the study.

The findings support the idea that allergies have increased, at least partially, thanks to the deficit of bacteria in modern living. Historically, food was loaded with bacteria and caused chronic immune responses that resulted in inflammation, says paediatric immunologist Anthony Horner at the University of California at San Diego.

Dirty Food

In the absence of such heavy bacterial exposure, the immune system is much less active than it should be and this leads to malfunction and can lead too allergies. "These probiotics are probably closely mimicking the effects of regularly eating unpasteurised and unsterilised food," Horner says.

Roger Katz, an allergist at the University of California at Los Angeles, School of Medicine, says the results are good news for people who know allergies run in the family.

"Even if someone has the genes for allergies, these results suggest that people can take action to at least reduce the chances of developing early allergic conditions like eczema," he says.