For the first time, it has been shown that asthma in children delivered by caesarean section is linked to an early perturbation in intestinal bacteria. The research, conducted by the Danish Pediatric Asthma Center, the University of Copenhagen and others, also demonstrates that the status of gut flora at around the age of one is a crucial determinant for the development childhood asthma. The new knowledge opens up the possibility of preventing the disease through supplemental probiotics.
For a number of years, it has been recognized that children delivered by caesarean section (C-section) have an elevated risk of developing asthma compared to those delivered vaginally. It has also been known that the composition of gut bacteria in children delivered by C-section differs early on. That there is a direct correlation between these two things has not been demonstrated until now.
"Now we know that a disturbance in bacterial flora in the intestine is one of the reasons why children delivered by C-section develop childhood asthma. Furthermore, we found that just a handful of bacteria make all the difference," says Professor Søren J. Sørensen of the University of Copenhagen’s Department of Biology.
His research team, together with the Danish Pediatric Asthma Center, which headed the study, analysed the effects of delivery methods on the gut microbiome – also known as gut flora – in 700 Danish children. They also investigated whether there is a correlation between disturbed gut flora as a result of C-section delivery and the development of asthma. In the study, researchers examined stool samples from the children several times during their first year of life. The study has just been published in the journal Science Translational Medicine.
Age one marks an important divide
In a vaginal delivery, a baby receives its first bacteria from the mother's birth canal as well as from feces and other things typically present at birth. On the other hand, when a child is delivered by C-section, and thereby unexposed to these bacteria, it lags behind in building up gut flora. Also new is that the study presents the age of one as a crucial dividing line.
"Children get off to a very different start. In most children delivered by C-section, gut flora correct themselves during the child’s first year of life, as a child is exposed to a variety of external environmental influences, such as older siblings. But for some, this doesn't happen before they reach one year of age. In these cases, their risk of asthma nearly triples," explains Jakob Stokholm, a physician and senior researcher at the Danish Pediatric Asthma Center at Herlev and Gentofte Hospital.
He adds: "Even if a child delivered by C-section has very perturbed gut flora early on, it does not necessarily lead to an increased risk of asthma — so long as the gut flora develop sufficiently by the age of one."
Probiotics may prevent asthma
Of the hundreds of types of bacteria found in children’s intestines, the researchers succeeded in identifying between five and ten types that seem to be the ones children lack and thereby cause the perturbation. The next step is to investigate these types of bacteria more closely and then perform experimental treatment regimens on mice with a bacterial cocktail.
"It is very encouraging that this new knowledge suggests that the disease can be prevented by correcting the composition of gut flora. In the long term, this can probably be accomplished by simply giving children a probiotic product containing the bacteria that their gut flora lacks before the age of one," concludes Søren J. Sørensen.
Stokholm J et al. Delivery mode and gut microbial changes correlate with an increased risk of childhood asthma. Science Translational Medicine. Vol. 12, Issue 569, eaax9929. DOI: 10.1126/scitranslmed.aax9929
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