Jeff has worked in both the chemical and biotech industries and is the veteran of thousands of science debates at cocktail parties and holiday dinners across the nation. In his Common Science blog, Jeff aims to make technological and scientific concepts accessible to all.

# Could Caesar Eat Peanuts?

Posted August 19, 2013 at 5:55 am

I recently had the chance to read through my stack of the last several months of Scientific American® magazine. My curiosity was piqued a story in one of the issues about a study conducted by the Henry Ford Hospital in Detroit. The study reported that babies who had been born via Caesarian section (C-section) were five times more likely to develop food allergies than those born vaginally. Like many parents I know, I have a strong impression that childhood food allergies are far more prevalent now than in the 1970s when I grew up. I have no childhood memories of peanut-free classrooms or EpiPens.

A search of the CDC and NIH websites provided the data for the graph below.

C-section rates have been steadily rising in the United States, from around 5% of births in 1970 to nearly 33% today. The data for childhood peanut and overall food allergies show that not only are childhood food allergies on the rise, but the rate of rise is nearly identical to the rate of increase of C-sections.

We’ll get back to the correlation been allergies and C-sections in a moment, but first permit me a brief aside to do a little math. I read several news reports on the Henry Ford Hospital study which all included the “five times more likely” statement, but omitted any absolute numbers. This is a key gap. For example, if C-sections increased the chance of developing a food allergy from 0.01% to 0.05%, it would probably not be significant enough to factor childbirth decisions.

However, using the data from the graph above and little algebra, it is not difficult to quantify the risks. If the 33% of children born via C-section are five times more likely to develop food allergies, and the total rate of allergies for all children is 5.1%, then the chance that a child born by C-section will develop a food allergy is 11.0% versus just 2.2% for a child born vaginally. This is a noteworthy difference and likely worthy of some consideration by expectant parents.

Getting back to the graph, we can see that childhood food allergies and rates of Caesarian births are closely correlated, but correlation does not necessarily demonstrate causation. The study at the Henry Ford Hospital addressed this issue and developed a convincing case for causation. While in-utero, the gastrointestinal (GI) tract of a child is bacteria free. Beneficial bacteria in your GI tract are essential both to digest food and to ward of disease. Therefore, newborn babies need to rapidly develop a large and diverse population GI tract bacteria.

During a vaginal birth, the baby’s GI tract becomes populated with the mother’s bacteria from the ingestion of fluids through the mouth. This “inoculation” of bacteria from the mother gives the child a tremendous head start towards developing a healthy digestive system. Babies born by C-section only start to populate their GI tract with bacteria from breast milk and/or from sticking their fingers in their mouths. This less efficient approach to establishing a healthy bacteria population appears to dramatically increase the incidence of food allergies. Food allergies may lack a scary-sounding name, but they are by no means a trivial circumstance. Sufferers can experience reduced quality of life, severe reactions, and, in extreme cases, death.

The parallels between this column and the issues I discussed in my recent column entitled “The Perils of a Hyper Hygienic Existence” are striking. Through the use of antibiotics some people have the population of healthy bacteria in their GI tract dramatically reduced in a sustained manner. This circumstance can bring about debilitating diarrhea and a variety of other serious GI tract problems. Recent studies have shown that these patients can experience remarkable improvement by introducing the bacterial flora from a healthy donor by a process rather unfortunately named fecal transplant.

When considering the correlation between Caesarian birth rates and food allergies I thought a similar solution might be appropriate. When Caesarian births are performed, I thought that a methodology might be considered which would introduce the mother’s bacterial flora to the child’s GI tract to help fend off food allergies.  I found a recent study conducted in Venezuela which did just that. They gave the child the bacteria she needed with a simple mouth swab after the C-section. This simple procedure could dramatically reduce the incidence of food allergies in C-section babies.

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