Prenatal exposure to maternal cigarette smoking appears associated with an increased risk for adolescent obesity, and is possibly related to subtle structural variations in the brain that create a preference for eating fatty foods, according to a Canadian study.

"Prenatal exposure to maternal cigarette smoking is a well-established risk factor for obesity, but the underlying mechanisms are not known," the authors wrote in background information for the study, which appeared Sept. 3 on the website of the Archives of General Psychiatry. "Preference for fatty foods, regulated in part by the brain reward system, may contribute to the development of obesity."

Amirreza Haghighi, MD, of the Hospital for Sick Children in Toronto, and colleagues studied 378 adolescents age 13 to 19 who were recruited through high schools in one region of Quebec as part of the ongoing Saguenay Youth Study. Participants were grouped as exposed or not exposed to maternal smoking and were matched at recruitment by maternal education and school attendance to minimize the influence of socioeconomic status. Participants in each group did not differ by sex, age, puberty stage or height.

The authors defined exposure as having a mother who smoked more than one cigarette a day during the second trimester of pregnancy, and non-exposure as having a mother who did not smoke one year before (and throughout) the pregnancy.

Compared with non-exposed participants, exposed participants weighed less at birth and were breast-fed for shorter periods of time. At the time of analysis, exposed participants had a marginally higher body weight and BMI and significantly higher total body fat compared with non-exposed participants. These differences persisted after adjustment for age, sex and height, and still were significant when adjusting for additional variables frequently associated with maternal smoking during pregnancy such as lower birth weight, shorter duration or lack of breast-feeding and lower socioeconomic status.

Exposed versus non-exposed participants also exhibited a significantly lower volume of the amygdala, the part of the brain that plays a role in processing emotions and storing memories. The authors found that, consistent with its possible role in limiting fat intake, amygdala volume correlated inversely with fat intake.

"Prenatal exposure to maternal cigarette smoking may promote obesity by enhancing dietary preference for fat, and this effect may be mediated in part through subtle structural variations in the amygdala," the authors wrote.

The study abstract is available at http://archpsyc.jamanetwork.com/article.aspx?articleid=1356544.