C-section babies more vulnerable to allergies

Baby in blanket
Only in the last few years have we come to realise that exposure to bacteria in the birth canal influences babies’ immune systems. Recent papers have shown that a c-section baby has a different pattern of gut bacteria than a baby born vaginally.
Dr Christine Cole Johnson
The patterns of bacteria and other microorganisms present in a babies’ gut may provide an indication of their risk of developing asthma and allergies at a very early age. According to research from Henry Ford Hospital in Detroit, the exposure to microorganisms that a baby receives in its mother’s birth canal provides an important foundation for establishing immunity to the extent that infants born by caesarean section (c-section) are at a considerable disadvantage when it comes to common allergies.

Dr Christine Cole Johnson, chair of the Department of Public Health Sciences at Henry Ford Hospital, presented the findings of the study so far at the annual meeting of the American Academy of Allergy, Asthma and Immunology in San Antonio, Texas, on Sunday. She was able to answer some questions for ScienceOmega.com on the implications of this ongoing work.

"At the AAAAI meeting last weekend, the gut microbiome in a human was referred to as one of our ‘metabolic organs’," Dr Johnson related. "New technology allows the measurement of the patterns of bacterial taxa in the gut and other parts of the body, and so the extent to which the bacterial ecology of the gastrointestinal tract impacts on our health is being recognised more and more. The gut is also our biggest immune organ, so anything that affects the ecology of the gut is likely to have a strong impact on our bodies."

In the United States, the National Institutes of Health are funding the Human Microbiome Project website, which aims to map the microbial community of human bodies. This and other similar projects are revealing the secrets of the microbiome and its complex influence on all aspects of our health.

"Only in the last few years have we come to realise that exposure to bacteria in the birth canal influences babies’ immune systems," Dr Johnson said. "Recent papers have shown that a c-section baby has a different pattern of gut bacteria than a baby born vaginally."

A total of 1258 newborns were enrolled on the study between 2003 and 2007, and the team followed this birth cohort from pregnancy through to two years of age. According to Dr Johnson and her colleagues, c-section babies are more susceptible to develop sensitivities when exposed to high levels of the allergens associated with cockroaches, dust mites, cats and dogs. They have a specific pattern of microbial activity in their gastrointestinal tracts which may increase the production of immunoglobulin E (IgE), the class of antibody found in mammals which plays a role in hypersensitivity – the development of allergic conditions and diseases.

"We collected data on their delivery, blood samples from the mother and father, family history of asthma and allergies, and dust samples from their houses," outlined Dr Johnson. "We measured common allergens in the dust, using measures from six months of age, and took blood samples at two years of age to detect evidence of sensitisation (in the form of IgE) to those same allergens. Sensitisation does not equal allergy, but is a necessary first step."

The researchers found that babies born by caesarean section were five times more likely than those born naturally to have developed sensitivity to common allergens by the time they were 24 months old. As Dr Johnson pointed out, there is a great amount of interest in this area, and a lot of effort is going into research on it. Studies such as this one, it is believed, are getting to the underlying mechanisms of the ‘hygiene hypothesis’ – the idea that a lack of exposure to microorganisms, infectious agents and parasites in early childhood can suppress the development of the immune system – which has been around for a number of years but has undergone some revisions since it was first proposed.

As for Dr Johnson and her colleagues, they have a number of ongoing projects, including one with the same cohort of children.

"We are going to bring them in for another clinical exam this year, and we also have frozen stool and dust samples from when they were babies," explained Dr Johnson. "We are in the process of assessing the microbiomes of those samples using a technology called the Phylochip. These tests are being carried out along with our colleagues at the University of California, San Francisco (UCSF), Dr Susan Lynch and Dr Homer Boushey."

While c-sections can obviously save the lives of mothers and babies, these findings will give some food for thought to those pregnant women considering an ‘elective’ c-section who are weighing up the risks and benefits. Asked if she has any advice for expectant mothers regardless of whether they are facing a caesarean birth, Dr Johnson said:

"Personally, based on the current weight of evidence, I would avoid the approach that some moms take of trying to keep an ‘antiseptic house’."

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