According to the researchers, the findings may shed more light on the increased incidence of asthma in recent decades.
It has been found previously that babies born naturally are exposed to maternal vaginal and intestinal bacteria, while babies delivered by caesarean are not.
Researchers argue that a lack of exposure to such pathogens can be bad for the immune system. They theorize that in the absence of such exposure, immune systems become sensitised to harmless materials, for example, dust or pollen, consequently resulting in conditions such as allergies and asthma.
“Too hygienic a birth without a welcome dose of mother’s microbes might give rise to a hypersensitive future in a genetically susceptible baby,” Nature quoted allergist Maria Pesonen of the Helsinki Skin and Allergy Hospital in Finland, as saying.
In the current review, Suren Thavagnanam at the Royal Belfast Hospital for Sick Children in Northern Ireland and his colleagues, conducted a meta-analysis of the results from 22 previous studies on the subject, to see whether they could get a firmer answer from more data.
After thorough analysis, the team revealed that there is a 20 per cent increase in asthma risk in children delivered by c-section.
“That’s an eyebrow-raising figure,” said Pesonen. Although noting that the figure of 20 per cent may be an overestimation, she added that the result seems “plausible”.
The incidence of asthma in UK children is now more than four times higher than it was in 1973.