Abstract 004: Physical Activity, Television Watching and Genetic Predisposition in Relation to Body Mass Index in Women and Men

Background Previous studies on gene-lifestyle interaction and obesity have largely focused on a single locus, the FTO gene, and overall physical activity, while little attention has been given in the association for sedentary activity as indicated by television (TV) watching. We examined the interactions between leisure-time physical activity and TV watching and the genetic predisposition to increased body mass index (BMI). Methods Longitudinal data were obtained from 7740 women and 4564 men from 2 prospective cohorts: the Nurses’ Health Study and Health Professionals Follow-up Study. Data on physical activity and TV watching were collected 2 years prior to assessment of BMI. A genetic predisposition score was calculated on basis of 32 established BMI-predisposing variants. Results Overall, each additional BMI-increasing allele was associated with an increase of 0.13 (SE 0.01) kg/m 2 in BMI. The effect size for BMI in individuals in the highest physical activity quintile was attenuated compared to that in individuals in the lowest physical activity quintile (0.08 [0.02] vs 0.15 [0.02] kg/m 2 ; P for interaction <0.001). In contrast, the genetic effect on BMI was more pronounced in individuals who spent >40 h/wk of TV watching than that in individuals who spent 0-1 h/wk of TV watching (0.34 [0.10] vs 0.08 [0.04] kg/m 2 ; P for interaction =0.001). Each 4 Mets/d increment in physical activity (equivalents to 1h/d of brisk walking) was associated with a 0.06 (95% CI 0.03-0.08) kg/m 2 reduction in BMI (∼46% of the main effect of each additional BMI-increasing allele), while each 2 h/d increment in TV watching was associated with a 0.03 (0.01-0.06) kg/m 2 increase in BMI (∼23% of the main effect). We estimated that the difference in BMI (∼4.0 kg/m 2 , equivalents to 11.6 kg in body weight for a person 1.70 m tall) between individuals with a genetic predisposition score of 13 (minimum) and those with a score of 43(maximum) could be reduced by half (2.1 kg/m 2 , 6.1 kg in weight) by 1 h/d of brisk walking or increased by 25% (5.0 kg/m 2 , 14.5 kg in weight) by 2h/d of TV watching. Conclusions Greater leisure-time physical activity attenuates the genetic predisposition to increased BMI, whereas sedentary lifestyle indicated by prolonged TV watching accentuates the genetic effects on BMI. Our data suggest that both increasing exercise levels and reducing sedentary behaviors, especially TV watching, independently may mitigate the genetic predisposition to increased BMI.