Allergy Onset


The risk of developing allergies by the age of 2 years old is five times greater for babies born by caesarean section (C-section) instead of natural birth. According to a study funded by Henry Ford Hospital, Detroit, and the National Institute of Allergy and Infectious Diseases, a baby’s exposure to bacteria in the birth canal can translate to a healthier immune system.

The researchers evaluated more than 1,200 newborns at four age intervals. The study’s findings are in line with previous research that demonstrates the important role of gut bacteria in the development of a healthy immune system. According to researchers, a C-section may alter or delay the development of normal bacteria in the baby’s gut.

The study’s lead author Christine Cole Johnson, PhD, MPH, chair of the department of public health sciences at Henry Ford Hospital , said these babies have a pattern of “at-risk” microorganisms in their gastrointestinal tract that may make them more susceptible to developing the antibody immunoglobulin E (IgE) when exposed to allergens such as pet dander and dust mites.

According to the American Academy of Allergy, Asthma & Immunology, the immune system of an allergic individual overreacts to an allergen by producing IgE. These antibodies travel to cells that release chemicals, causing an allergic reaction. This reaction usually causes symptoms in the nose, lungs, throat, or on the skin.

“We know the prenatal and early post-natal environments are important to immune development, and other health related issues but the role of infants’ microbiota is a very new concept,” Johnson observed. “Many people are scrambling to figure out what effect this has.”

Study Parameters
The study enrolled 1,258 newborns from 2003 to 2007, and evaluated them at one month, six months, one year and two years. The researchers collected data from the babies’ umbilical cord and stool, blood samples from the babies’ mothers and fathers, breast milk and household dust, as well as family history of allergy or asthma, pregnancy variables, household pets, tobacco smoke exposure, baby illnesses and medication use.

The study measured allergy risk in C-section babies by looking at dust mite, cockroach, dog and cat allergen levels in the home. Children exposed to these allergens, the study found, had a higher rate of sensitization at 2 years old. “The children who were not exposed, weren’t sensitized,” Johnson said. “But it was the combination of C-section and exposure to the allergens that resulted in children with allergic sensitization.”

According to Johnson, doctors used to tell people with a family history of allergic diseases that their children should avoid exposure to allergens. “We no longer suggest people avoid the allergens,” she said. “But now, we might have discovered the whole infrastructure behind why we react one way or another to allergen exposure.”

This research is important for expectant moms who may contemplate the pros and cons of natural childbirth or C-section, said Johnson. “The birth process takes a while for a reason,” she observed. “When a baby travels down the birth canal, he is exposed to so much immune stimulation all at once. We are just beginning to appreciate the impact this journey has on a child’s health later on.”

Johnson is quick to point out that birth by C-section is just one risk factor for allergies. “C-sections may contribute to the risk of developing allergies but other factors can enhance or wipe out that risk,” Johnson told ADVANCE.

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