C-section Not Tied to Childhood Asthma

NEW YORK (Reuters Health) - In theory, whether a child is born by cesarean section or in the normal way via the birth canal could affect his or her chances of developing asthma later in life -- but that notion apparently does not hold up in reality.

The mode of delivery at birth appears to have no bearing on the subsequent development of asthma, researchers report.

The development of allergies and asthma is thought to be influenced by the type of infections a child is exposed to very early in life, which in turn sets the immune system to respond normally or over-sensitively to allergens. The so-called 'hygiene hypothesis' holds that children who are overly protected against bacteria tend to develop allergies, because they need the exposure to develop a balanced immune system.

"Bacterial colonization of the gut in newborns delivered by cesarean section differs from that in newborns born by vaginal delivery," lead investigator Dr. Young J. Juhn told Reuters Health. This may influence the development of allergies.

As reported in the Journal of Allergy and Clinical Immunology, Juhn and colleagues examined data for more than 7000 children -- 10 percent of whom were delivered by cesarean section -- to see if different bacterial exposure influenced the risk of asthma development or wheezing.

Over 7 years, the asthma occurred at a rate of 3.2 to 5.7 percent in the cesarean group and 2.6 to 6.7 percent in the vaginal delivery group. The differences were not significant from a statistical standpoint.

The investigators conclude, "Either the underlying assumption of the hygiene hypothesis in assessing the influence of microbial organisms on development of (allergies) may be too simplistic conceptually and methodologically, or the influence of microbial organisms ... may be weaker than what has been reported."

SOURCE: Journal of Allergy and Clinical Immunology, September 2005.