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Television Watching, Leisure Time Physical Activity and the Genetic Predisposition in Relation to Body Mass Index in Women and Men
Study Questions:
Do behaviors such as television watching and physical activity influence the relationship between genetics and body mass index (BMI)?
Methods:
The investigators used data from the Nurses’ Health Study (NHS) and the Health Professionals Follow-up Study (HPFS). The NHS is a prospective cohort study of 121,700 female registered nurses who were 30-55 years of age at study inception in 1976. The HPFS is a prospective cohort study of 51,529 US male health professionals who were 40-75 years of age at study inception in 1986. Study samples for the present analysis included participants of genetically inferred European ancestry from NHS and HPFS, with genome-wide association study data that were initially designed to address various chronic diseases such as type 2 diabetes mellitus, coronary heart disease, kidney stone disease, open-angle glaucoma, and breast cancer (NHS only). A total of 32 single-nucleotide polymorphisms (SNPs) that demonstrated significant genome-wide association with BMI in a recent meta-analysis were used in a weighted genetic risk score. Self-reported physical activity and TV watching were collected 2 years prior to measure of BMI. TV watching was divided into five groups by hours, from 0-1 hour to >40 hours.
Results:
A total of 7,740 women from the NHS and 4,564 women from the HPFS (n = 4,423), were included in this analysis. For both women and men, the genetic associations with BMI were stronger with increasing hours of TV watching. An increment of 10 points in the weighted genetic risk score was associated with 0.8 (standard error [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/m2 higher BMI across the five categories of TV watching (0-1, 2-5, 6-20, 21-40, and >40 hours/week; 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/m2 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:
The investigators concluded that a sedentary lifestyle, indicated by prolonged TV watching, may accentuate the predisposition to elevated adiposity. In contrast, greater leisure time physical activity may attenuate the genetic association with BMI.
Perspective:
These novel findings suggest that lifestyle behaviors such as regular physical activity are critical to prevention of obesity, particularly among those with a genetic predisposition towards increased BMI.
Keywords: Television, Women, Body Mass Index, Body Composition, Polymorphism, Single Nucleotide, Leisure Activities
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