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Allergy Onset

Study finds an association between caesarean birth and allergy risk

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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How Important is Gut Health?
Johnson and her team explore research projects based on the important role that gut microbiome plays in setting up the immune system and its defenses. "All humans have microbes in their bodies," she revealed. "Aside from the organisms we know perform vital tasks essential for our survival, the exact role played by the balance of the rest of the microbes is virtually unknown."

The gut-associated lymphoid tissue (GALT) is the biggest immune organ in the body. An individual's gut health is important, Johnson explained.

Johnson decided to explore this topic because the medical literature had suggested an association. "I learned that C-section puts babies at higher risk for allergies such as dermatitis and asthma," she said.

According to Johnson, numerous microbiology studies have looked into the connection between microbiota and immune defenses. Studies attempt to explain why healthy individuals are able to maintain a balanced coexistence with microorganisms while others contract an infection when the balance of microorganisms is disrupted.

Studies have found in early infancy that the gut microbiome of babies born by C-section is more similar to the mother's skin microbiome than her gut microbiome. "This is likely not good for the health of these children," Johnson said.

A few years ago, Henry Ford Hospital conducted a birth study in which the investigators saved diaper stool samples and froze them. "We brought children in at age 2 and now at 10 years old to study their allergy status," Johnson said. "Because of the stool samples, we can then look at the microbiome in infants and see if it is predictive of their allergy status. We identify the species and try to determine if there is a pattern."

Due to advancements in testing technology, the ability to analyze bacteria from previously collected samples is new to Johnson and her fellow investigators. "We have only recently, within the last 10 years, been able to explore this area," she said. "It has exciting possibilities."

Even though there are thousands of bacteria types in the human gut, in the past researchers could only study a few at a time. "It was only realistic to study six or seven at a time, which isn't much, but even so researchers could detect some differences between children who developed allergies and those who did not," Johnson said.

Johnson suggests avoiding the use of antibiotics-for mother and child-when their use is not absolutely necessary. "Antibiotics can mess up the gut," she shared. "Mothers need to be vigilant and ask the doctor, 'does my child really need this antibiotic?'"

If a mother has been on antibiotics during pregnancy and prior to giving birth via C-section, then the baby's microbiome may be affected. Johnson and her team are exploring this systemic effect in a new research study at Henry Ford Hospital.

Fighting off Infection
"The immune system has different cells standing by to fight off pathogens," Johnson explained. "When the immune system fights back, you have inflammation which is an indication that your immune system is working. You have other important cells that will stop the inflammation when it is no longer needed."

In some people, according to Johnson, the part of the immune system that regulates the inflammatory response does not work optimally. Inflammation is sustained, chronic or inappropriate. The immune system needs to learn how to recognize bad and good bacteria.

Other research studies have suggested that C-section babies are more susceptible to food allergies. Although Johnson hasn't studied that specific connection, she explained that food is a foreign antigen, like pet dander, and the immune system has to figure out what is good and bad. "Our bodies need to learn when to build defenses and when not to," Johnson shared.

Researchers, including Johnson, are beginning to recognize the large role that inflammation plays in immune health. Accordingly, the Henry Ford Hospital study has potential implications down the line for autoimmune diseases, including lupus, multiple sclerosis and juvenile diabetes, where the immune system starts attacking its own cells, as well as other chronic diseases.

According to Johnson, the number of studies on human microbiome and health is relatively small but the passion of the researchers is immeasurable. "There is not a lot known in this area of study and researchers are working hard behind the scenes to catch up," she said. "Right now, there's a lot of interest in the early part of life and its impact on a lifetime."

Rebecca Mayer Knutsen is on staff at ADVANCE. Contact:

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I think the study on the immune system being spot on. But... I have a daughter born by C-section 8 weeks premature, we have cats since before she was born, and she is the healthiest out of my 5 children. All of my other children have been born naturally, and to some degree all but one, have some sort of allergy needing prescription allergy meds and to see an allergist for testing. There have got to be some other factors in what good or bad bacteria/viruses/fungus can do to the unborns immunity. Were all of the mothers of the study tested immunologically while pregnant and then after? We all the mothers exposed or not exposed to unknown factors while pregnant? When you get down to it, you cannot say for sure if it really is a c-section that causes a higher rate of allergies. You would also have to follow that child and the mothers for life to check in to see if the non c-section children did develop allergies down the road. Too many variables to consider. My husband born by c-section, has sleep apnea, asthma and allergies as an adult, but not when a child. He has a high stress job now. Maybe that could be a factor. We know stresses can play a role on immunity. Malnutrition could also play a factor as well as Vitamin D Deficiency. Gluten can trigger IgG not IgE, but who knows how it can affect your body as a whole. The medical community wants to look at each individual body system, you cannot do that. The body is a whole, one system will in turn affect another system eventually. Thank you for your time.

Bethany MericleMarch 27, 2015
Lima, OH


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