Study explains link between Caesarean birth and allergies

Children born via Caesarean section run a higher risk of developing allergies due to a lack of bacteria in the gastrointestinal tract, according to a study which involved KTH Royal Institute of Technology’s Science for Life Laboratory.

The researchers tracked the development of intestinal flora among 24 children in Sweden over a period from birth to the age of 2. Nine of the children were born by Caesarean section and 15 via vaginal delivery.

Through molecular biological analysis, the team was able to get a broad overview of the genera of bacteria found in the gut. They found that children delivered by Caesarean section had less diversity of flora in their intestines. In particular they lacked the bacterial group Bacteroidetes which, according to the research team’s earlier observations, are associated with protecting against allergies.

The research team included the study’s lead author Anders Andersson, a researcher in metagenomics at KTH’s Science for Life Laboratory. The results are presented in the journal Gut.

“Caesarean section is sometimes necessary,” says Maria Jenmalm, Professor of Experimental Allergology at Linköping University and an author of the article. “However, it is important that both mothers and doctors are aware that such delivery may affect the baby's health.”

Diabetes and irritable bowel syndrome also are more common among children born by Caesarean.

Up to the moment of birth, the child’s gut seems to have completely sterile. Colonization by many different bacteria seems to be necessary in the first few years in order for the immune system to develop and mature. Otherwise, the system overreacts to harmless antigens in the environment, such as food. Children suffering from such allergies face a six times higher risk of developing asthma at school age.

But in a natural childbirth, the child is exposed to bacteria from the mother's vagina and anus, which provides a good start for the child's own intestinal flora.

Those who arrive by an incision in the mother's abdomen may require other measures, Jenmalm says. “Maybe it's not so good with exclusive breastfeeding for six months. Early taste of regular food could encourage greater diversity in the gut flora.”

A more radical approach is now going to be examined by scientists in Puerto Rico, who screened the vaginal flora of pregnant women before their planned Caesarean. After the birth, the midwife takes a swab with secretions from the mother's vagina and rubs it into the baby's face. The hypothesis is that in this way, important bacteria can be provided to the baby. A similar study is planned in Sweden.

In addition to a greater diversity of intestinal flora, researchers in Sweden have also found that children born vaginally had higher blood plasma levels of substances linked to Th1 cells, a kind of "chief cell" of the immune system that may inhibit allergic immune responses.

The intestinal flora can be considered as the body's largest organ. There is at least 10 times more flora in the small and large intestine of an adult human than there are cells in the entire body. More than 100 species of flora can be found in the gut. They use the nutrients in the food we eat, and some of them form antibiotic-like substances that can kill offensive germs.

“Recent advances in biotechnology have made possible new insights into this fascinating universe of bacteria. With modern methods of DNA sequencing and computer analysis, we can determine the species composition of hundreds of samples simultaneously, and even get a glimpse into what properties bacteria possess,” Andersson says.

The scientific article is titled "Decreased gut microbiota diversity, delayed Bacteroidetes colonization, and reduced Th1 responses in infants delivered by Caesarean section," and was published on August 7 in GUT. In addition to Andersson and Jenmalm, the authors are H.E. Jakobsson, T.R. Abrahamsson, , K. Harris, C. Quince, C. Jernberg, B. Björkstén, and L. Engstrand.

Other researchers who participated in the study work at Stockholm’s Karolinska Institute, Örebro University and the University of Glasgow, Scotland.

The study was conducted with the support of Ekhaga Foundation, Ragnar Söderberg Foundation, the Swedish Research Council, FORSS, Asthma and Allergy Association, Stiftelsen Olle Engkvist, Vårdalsstiftelsen, Formas and Unilever.

For more information, contact Anders F. Andersson at +46 (0) 73-983 89 62 or Maria Jenmalm at +46 (0) 70-237 89 70.

Åke Hjelm / Peter Larsson