Television watching, leisure time physical activity, and the genetic predisposition in relation to body mass index in women and men.

BACKGROUND: Previous studies on gene-lifestyle interaction and obesity have focused mostly on the FTO gene and physical activity, whereas little attention has been paid to sedentary behavior as indicated by television (TV) watching.

METHODS AND RESULTS: We analyzed interactions between TV watching, leisure time physical activity, and genetic predisposition in relation to body mass index (BMI) in 7740 women and 4564 men from 2 prospective cohorts: The Nurses' Health Study and the Health Professionals Follow-up Study. Data on physical activity and TV watching were collected 2 years before assessment of BMI. A weighted genetic risk score was calculated on the basis of 32 established BMI-associated variants. In both women and men, the genetic associations with BMI strengthened with increased hours of TV watching. An increment of 10 points in the weighted genetic risk score was associated with 0.8 (SE, 0.4), 0.8 (SE, 0.2), 1.4 (SE, 0.2), 1.5 (SE, 0.2), and 3.4 (SE, 1.0) kg/m(2) higher BMI across the 5 categories of TV watching (0-1, 2-5, 6-20, 21-40, and >40 h/wk; P for interaction=0.001). In contrast, the genetic association with BMI weakened with increased levels of physical activity. An increment of 10 points in the weighted genetic risk score was associated with 1.5 (SE, 0.2), 1.3 (SE, 0.2), 1.2 (SE, 0.2), 1.2 (SE, 0.2), and 0.8 (SE, 0.2) kg/m(2) higher BMI across the quintiles of physical activity. The interactions of TV watching and physical activity with genetic predisposition in relation to BMI were independent of each other.

CONCLUSIONS: A sedentary lifestyle, indicated by prolonged TV watching, may accentuate the predisposition to elevated adiposity, whereas greater leisure time physical activity may attenuate the genetic association.