Danish researchers provide proof: Caesarean sections can lead to asthma and allergies

Danish researchers provide proof: Caesarean sections can lead to asthma and allergies

Delivery by caesarean sections changes the composition of the newborn baby’s gut microbiota. And it turns out that Caesarean sections can also trigger diseases. However, it should largely be possible to prevent these diseases with beneficial bacteria. A team of Danish researchers has reached this opinion based on novel results – and they now have a cocktail of these beneficial bacteria on the drawing board.

C-sections often save lives – both the baby’s and the mother’s – but they can also have a downside.

Researchers have been aware for some time that children born by C-section are more likely to develop asthma and allergies than those born by vaginal delivery.

The theory is that C-section-born children do not receive the natural microbiome from their mother that they would otherwise receive if delivered vaginally – and this can change the composition of the baby’s gut microbiota, making them vulnerable to asthma, allergies and other diseases associated with the immune system.

It is difficult to prove scientifically that changes in gut microbiota due to delivery by C-section do indeed increase the risk of developing asthma and allergies – but a team of researchers from the Copenhagen Prospective Studies on Asthma in Childhood, University of Copenhagen, the Technical University of Denmark and American Rutgers University have now managed to do so.
Their study, which has received funding from the Lundbeck Foundation, was recently published in the highly prestigious scientific journal Science Translational Medicine.

‘To cut a long story short, we prove that the risk of children born by caesarean section developing asthma is up to two and a half times greater than for children born by vaginal delivery,’ says Jakob Stokholm, senior scientist at the Copenhagen Prospective Studies on Asthma in Childhood and first author of the scientific article.

The study also indicates that C-section-born children have a significantly higher risk of developing allergies compared to children delivered vaginally.



In wealthy parts of the world, caesarean procedures are on the increase, and have been for a number of years.

In Denmark, around 20% of all children are now born by C-section – whereas caesarean section prevalence is slightly more than 30% in North America and more than 40% in Latin America (The Lancet, 2018). In any case, these numbers exceed the recommendations of the World Health Organisation (WHO), which believes that no more than 15% of all births should end in caesarean section.

To identify the correlation between caesarean section and asthma, the Danish-American research team analysed data from the COPSAC2010 Mother-Child Cohort.

This study, conducted by researchers from the Copenhagen Prospective Studies on Asthma in Childhood, follows 700 Danish children born between 2009 and 2011.
The researchers regularly collected samples from the children, including samples from gut bacteria, skin and bacterial composition in the children’s respiratory tracts.
And this new proof of the correlation between birth by C-section and development of asthma and allergies is based on some of these samples.



Jakob Stokholm explains that the researchers found something extremely interesting when they compared the composition of the gut microbiota of the vaginally-born children in the COPSAC2010 study (78% of the cohort) with the gut microbiota of the 22% who were delivered by caesarean section:

‘We could see that some of the children delivered by C-section – whose gut microbiota at birth was somewhat different from that of the vaginally-delivered children – actually recovered during the first year of life. They developed a completely normal microbiome, and when we studied the health of these C-section-born children at around the age of six, we found that their incidence of asthma and allergies was no higher than that of the COPSAC2010 children who had been born by vaginal delivery. On the other hand, the C-section-born children whose gut microbiota had not normalised during the first year of life had a significantly higher risk of developing asthma in the longer term.’

The researchers are not 100% sure why some of these children delivered by caesarean section developed a normal microbiome during their first year. However, there is much to indicate that the presence of siblings in the home may be part of the explanation. The hypothesis is that older siblings unknowingly transfer healthy bacteria to their younger brother or sister when they touch them; for instance, while playing.

Jakob Stokholm points out that the discovery that it is possible to develop a normal microbiome, even if you are born by C-section, thus eliminating an excess risk of developing asthma and allergies, is a highly significant breakthrough: ‘It indicates treating children born by C-section with, for example, probiotics – in other words, giving them bacteria that are beneficial for the gut.’

Professor Søren J Sørensen, from the Department of Biology at the University of Copenhagen, was responsible for characterising the content of the bacteria in the samples on which the scientific article in Science Translational Medicine is based, and he agrees fully with the perspective for prevention:

‘It’s very encouraging, and it indicates that, in time, it may be relatively easy to prevent some types of asthma by giving these children a probiotic containing the bacteria lacking in their gut microbiota – before they reach the age of one.’

Jakob Stokholm says that development of this probiotic is already on the drawing board.


Foreign studies are also investigating the significance of the bacteria a child receives from its mother during a vaginal birth. For example, a forthcoming Swedish study will give children born by C-section both vaginal bacteria and gut microbiota from their mother to see whether this could prevent disease.

Another study, recently completed by Dutch and Finnish researchers, involves transferring gut microbiota from the mother to the C-section-born infant. These bacteria were mixed with breast milk.



COPSAC is a clinical research unit, and the acronym stands for: Copenhagen Prospective Studies on Asthma in Childhood. The research unit is run by Professor Hans Bisgaard, under the auspices of Herlev and Gentofte Hospital. Over the years, the Lundbeck Foundation has provided COPSAC with funding to the tune of DKK 86 million.


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