Follow-up allergy tests — conducted at age 1 and age 3 — confirmed that, on average, babies with low Bacteroides levels were three times more likely to develop peanut sensitivity by age 3.
“We found a causal link between cesarean section birth, persistently low Bacteroides in the first year of life, and peanut sensitivity in infants,” noted study author Hein Tun, an assistant professor in the school of public health at the University of Hong Kong.
That’s a problem, said Tun, because “as the gut microbiota are developing so is the gut’s immune system, training the gut to react to pathogens and to be tolerant of the food that we require.”
In fact, low Bacteroides levels linked to C-section deliveries is really only part of the concern, Tun’s team noted, because low Bacteroides levels also tend to be accompanied by low levels of sphingolipids, proteins that are key to healthy immune system development, further undermining food tolerance.
“[And] the effect is more pronounced in children of Asian descent than others,” Tun added. He and his colleagues found that low Bacteroides levels in Asian infants were linked to an eight-times higher risk for developing a peanut allergy.
Tun deemed that later finding “a bit of a surprise,” though he attributed the stark increase in risk to the fact that many of the Asian infants in question had immigrated to Canada.
“[So] it’s likely related to a change in diet and environment that lead to the Westernization of [their] gut microbiota,” Tun said, though he acknowledged that more research is needed to confirm the hypothesis.
Still, the general finding of a C-section link to peanut allergies comes as little surprise to Lona Sandon, program director of the department of clinical nutrition with the school of health profession at the University of Texas Southwestern Medical Center at Dallas.
The link between C-sections and immune system issues among infants “is fairly common knowledge and consensus within the pediatric and nutrition world,” Sandon said.
“A C-section results in less exposure to germs or bacteria upon birth. Same with lack of breastfeeding,” she noted. “This lack of exposure affects the immune system’s ability to mature and adapt to life outside the womb. This lack of exposure and maturity is also associated with inappropriate immune reactions such as food allergies.”
