Sensitization to food allergens often occurs early in the preschool years. While not all kids who develop food sensitivities end up with full-blown allergies, it is often considered the precursor to the development of allergies and asthma. These conditions are typically grouped together under the term atopic disease because of their tendency to be caused by over active IgE, an antibody in your blood. This IgE latches onto allergens in everyday objects you come in contact with and initiates the allergic response. Atopic diseases include asthma, anaphylaxis and eczema and it is not uncommon for someone with atopic disease to develop all forms of the disease at some point in their life. This is called the atopic march.
One of the leading theories behind the development of atopic diseases, or an over active IgE response, is called the hygiene hypothesis. This hypothesis states that our excessive use of antibiotics for treatment of diseases that don’t need them as well as their use in cleaning supplies has led to the development of an immune system that is immature and uneducated in what is dangerous and what is not. This is because bacteria in our body, called our microbiome, play an important role in educating our immune system to prevent it from attacking things that are not dangerous, like foods. The bacteria in our gut are particularly important for this and are killed by antibiotics. Any loss of these bacteria or alterations in the makeup of this bacterial community can alter how the immune system develops. The lack of education of our immune system has actually been hypothesized to be associated with other autoimmune disorders.
The easiest way to understand this microbiome and its role in educating the immune system is to think of a child. Your child is will meet many people in their lifetime. If there are many good role models around for the child, then there is a greater chance that this child will grow up to understand right from wrong. If the child has more bad role models around, there is a greater chance the child will fail to understand right from wrong. The roles models in this examples are like the bacteria in your gut and th child is your young immune system. The good role models are the bacteria normally present and the bad role models being the bacteria that is present when the normal bacteria is missing. More bad bacteria, worse education for your immune system and the more likely it is to attack things it shouldn’t.
Researchers involved in the Canadian Healthy Infant Longitudinal Development Study or CHILD have been able to identify how changes in the gut microbiome of infants may be associated with the development of atopic disease. They collected fecal samples from 166 children at 3 months of age and again at 12 months of age to look for the types of bacteria that are colonizing the guts of these kids. Once they knew what kinds of bacteria were present, they tested these kids for food sensitivities by a skin prick test, the kind any kid with an allergy normally goes through. They then grouped the kids into those who had food sensitivity at 12 months of age and those who didn’t to see if the bacteria in their guts differed. Their results showed that children with food sensitivities were more likely to have a loss of bacteria richness or diversity early in life. They were also more likely to have elevated numbers of a bacteria, Enterobacteriacae, and more likely to have less of a bacteria, Bacteroidaceae. In fact, those kids who, at 3 months of age, had more diversity in their bacterial populations (more different types of bacteria) had about a 50% reduction in the risk for developing food sensitivity. Also, kids with a larger Enterobacteriacae to Bacteroidaceae ratio were twice as likely to develop food sensitivities. The interesting thing about these results is that they held true whether the kids were breast fed, birthed vaginally or by c-section or whether or not they had antibiotics early in life. This suggests that the babies start out with a defect in the colonization of their gut by bacteria rather than them developing this defect later in life due to some exposure (like antibiotics).
There is still plenty more work that needs to be done and the CHILD cohort is the prime setting to answer many of the questions. Primarily, it would be important to know how many of these children with food sensitivities will develop allergies and whether the type of bacteria in their gut is important in this transition. We also need to know whether something about the environment the kids are born into is affecting the initial colonization of their gut. Since the babies get their gut bacteria from their mother during birth, it is possible that some defect in the mothers microbiome is passed on to the babies. It is also possible that exposure to some chemical during pregnancy affects the babies gut making it more likely to be colonized by bad bacteria.
It should be noted that these results only hint at an association between bacteria and atopy and that there is still plenty of questions the hygiene hypothesis. More work still needs to be done to determine if the changes in the microbiome are a cause of atopy or just a bystander. We still don’t have all the answers but it seems more and more likely that bacteria are playing an important role in our health and the development of diseases like allergy and asthma. As such, more care needs to be taken when using antibiotics and antibacterial products. Don’t use them unless they are needed. For everyday use soap and water will do.