Large Study Identifies a Link Between Food Allergies and C-Section Delivery

It turns out that C-section births may carry an unexpected risk: food allergies. In a large-scale study of Swedish children, doctors found that kids delivered by C-section had a 21 percent higher risk of developing food allergies than those born by vaginal delivery.

For the study, an international team of researchers observed over 1 million children born between 2001 and 2012. Though they only tracked babies born in Sweden, not all the mothers involved were Swedish. The results, published September 10 in The Journal of Allergy and Clinical Immunology, add to the growing body of knowledge on the interactions between Cesarean births and allergies — and yes, it’s a large body. Previous studies have shown similar associations with C-section delivery, including an increased likelihood of milk allergies and increased likelihood of developing asthma.

It’s not totally clear why C-sections seem to increase the risk of food allergies, but over the past few years, researchers have developed some ideas. One potential explanation involves the “hygiene hypothesis,” which states that children who are exposed to a rich environment of microbes grow up to have fewer food allergies.

During a vaginal birth, a newborn baby’s microbiome gets colonized by its mother’s vaginal microbes as it enters the world. Since a baby delivered by C-section is deprived of this inoculation, the first microbial environment it encounters is usually that of a hospital room. According to the study authors, it’s possible that this increases the likelihood that the baby’s microbiome will be colonized by a disproportionately high percentage of the bacterium Clostridium difficile.

“Cesarean delivery seems to delay and alter the development of the offspring’s immune system, subsequently increasing the risk of atopic disease,” write the study’s authors, led by Niki Mitselou, a doctoral student at Örebro University in Sweden.

Another possibility, though, is that the indications for cesarean delivery could also be risk factors for food allergies. In other words, it may not be the Cesarean delivery itself that causes food allergies, but some other factor or factors may be to blame for both food allergies and for needing a C-section. However, since the study involved both emergency and elective C-section deliveries, it reinforces the idea that vaginal flora is at least partly responsible for inducing food tolerance.

Interestingly, while the researchers found an elevated risk of developing food allergies associated with a C-section birth, they found the opposite correlation with preterm births (less than 32 weeks). Preemie babies actually had a 26 percent lower risk of developing food allergies than the full-term vaginal birth babies.

“The observed negative association between very preterm birth and food allergy indicates that either very preterm birth per se or associated neonatal care initiated in very preterm-born children (including early introduction of foods orally) might be involved in the induction of tolerance to foods,” write the study’s authors. Whether it’s the foods given to preterm babies or the mere fact of being preterm, this finding supports the notion that neonatal care is essential in raising babies that can tolerate foods.