Babies delivered by Caesarean section may be at increased risk of becoming obese later in life, a new study suggests.
In the research, which included more than 38,000 people from 10 countries, the odds of being obese as an adult were 22 percent higher for those born by C-section, compared with those born by vaginal delivery.
And the odds of being overweight (but not obese) as an adult were 26 percent higher for those born by C-section.
The study adds to a growing body of research linking C-section births to obesity. A 2012 study of children in Massachusetts found that those born by C-section had double the odds of being obese at age 3. The new study is the largest to find a link between Caesarean delivery and weight in adulthood. [7 Ways Pregnant Women Affect Babies]
"There are good reasons why C-section may be the best option for many mothers and their babies, and C-sections can on occasion be life-saving," study researcher Dr. Neena Modi, of Imperial College London, said in a statement. "However, we need to understand the long-term outcomes in order to provide the best advice to women who are considering Caesarean delivery."
The study does not prove a cause-and-effect relationship between C-sections and obesity, however. It's possible that other factors not taken into account by the study, such as whether the mother was obese or had gestational diabetes, could explain the link.
Still, given the rising rates of C-sections worldwide, there is an urgent need to determine what's behind the link, the researchers said. Currently, about a third of babies born in the United States, and a fourth of babies born in England, are delivered by C-section.
In the new study, the researchers reviewed information from 15 previous studies that collected data on individuals' method of delivery when they were born, as well as their body mass index (BMI) in adulthood. (BMI takes into account a person's height and weight, and provides a measure of body fatness.) The average age of participants in these studies ranged from 18 to 70; researchers defined obesity as a BMI of more than 30, and overweight as a BMI between 25 and 30.
The link between C-section delivery and adult obesity was strongest among participants born more recently, indicating that the link may be of growing importance, the researchers said.
It's not clear how the link may work, but one explanation involves gut bacteria. The types of bacteria in the guts of babies born by C-section tend to differ from those born by vaginal delivery, the researchers said.
The study is published today (Feb. 26) in the journal PLOS ONE.