(HealthDay News) – The genetic predisposition to increased body mass index (BMI) is attenuated by increasing physical activity and accentuated by sedentary activity, such as watching television (TV).

Using longitudinal data from 7,740 women and 4,564 men, Qibin Qi, PhD, from the Harvard School of Public Health in Boston, and colleagues investigated the interactions between leisure-time physical activity and TV watching and the genetic predisposition to increased BMI. Thirty-two established BMI-predisposing variants were used to calculate a genetic predisposition score.

The researchers found that there was an increase of 0.13kg/m² in BMI for each additional BMI-increasing allele. Compared with individuals in the lowest quintile for physical activity, there was an attenuation of the effect size for BMI in individuals in the highest quintile (0.08 vs 0.15kg/m²). An increase in physical activity equivalent to one hour of brisk walking per day correlated with a 0.06kg/m² reduction in BMI. For individuals who spent more than 40 hours per week watching TV, compared with those who spend zero to one hour per week watching TV, the genetic effect on BMI was more pronounced (0.34 vs 0.08kg/m²). Each two-hour increase in TV watching correlated with a 0.03kg/m² increase in BMI.

“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,” the authors write.

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