New Research: Intestinal Bacteria and Allergies

One of the most perplexing issues in food allergy research today is that, while researchers can quantify an increase in severe food allergies, there has, thus far, been limited success in discerning the reason for that increase. Among the explanations with the most traction has been the "hygiene hypothesis." In simplified terms, the hygiene hypothesis is the idea that, because Westerners live in cleaner, more sanitized environments than the immune system is evolutionarily suited for, the immune system doesn't have the opportunity to act against bacteria and other microbes and instead responds by developing abnormal immune responses to foods and other otherwise harmless substances. Two studies in the August 2007 Journal of Allergy and Clinical Immunology examine different aspects of how the bacteria in the human intestines affect allergies.

The first study, a review by Drs. Susan Prescott and Bengt Björkstén, examines the potential role of probiotics in strengthening the immune system. Probiotics are a general term for "helpful" bacteria that colonize the gastrointestinal tract. Familiar examples include the bacteria used to culture yogurt. Because the hygiene hypothesis holds that lack of exposure to microbes early in life might have some role in allergy development, several studies have been conducted to determine whether probiotics might be sufficient to provide this exposure. Prescott and Björkstén's review concludes that 1.) no sufficient data exists to promote probiotics as general therapy for allergies; 2.) some studies show results from certain probiotics in the treatment of eczema in young children, although these should be confirmed with larger-scale studies and are not likely to be panaceas; 3.) people with a possibility of milk allergy should exercise caution in the use of probiotics, as many are derived from dairy; and 4.) prebiotics --- substances which stimulate the growth of probiotics in the intestines --- are a potential future area of study for allergy prevention.

A second study, led by Ingegerd Adlerberth, examined the bacteria in the intestines of three European birth cohorts (that is, groups of children born at the same time) to determine if there were any correlations between the bacteria in infants' intestines and later development of allergies. This study, the largest to date examining intestinal bacteria and demographic factors, studied children in three countries until the age of eighteen months. While researchers made several observations regarding patterns among infants delivered by Cesarean section, infants with older siblings, and infants who had been treated with antibiotics, none of these patterns in the intestinal bacteria translated into statistically significant results regarding development of food allergies or atopic eczema. Researchers noted that some allergic diseases (like hay fever or asthma) might develop later in life, and that "some noncultivable bacteria with strong immune-activating properties might remain undetected." While this study does not by any means disprove the hygiene hypothesis, in the researchers' own words, "the exact nature of the microbial stimulus required for normal tolerance development and protection from allergy in early infancy remains to be identified."