Background: Whether obesity is a cause or consequence of low physical activity levels and more sedentary time has not yet been fully elucidated. Better instrumental variables and a more thorough consideration of potential confounding variables that may influence the causal inference between physical activity and obesity are needed.
Methods: Leveraging results from our recent genome-wide association study for leisure time moderate-to-vigorous intensity (MV) physical activity and screen time, we here disentangle the causal relationships between physical activity, sedentary behavior, education-defined by years of schooling-and body mass index (BMI), using multiple univariable and multivariable Mendelian Randomization (MR) approaches.
Results: Univariable MR analyses suggest bidirectional causal effects of physical activity and sedentary behavior with BMI. However, multivariable MR analyses that take years of schooling into account suggest that more MV physical activity causes a lower BMI, and a higher BMI causes more screen time, but not vice versa. In addition, more years of schooling causes higher levels of MV physical activity, less screen time, and lower BMI.
Conclusions: In conclusion, our results highlight the beneficial effect of education on improved health and suggest that a more physically active lifestyle leads to lower BMI, while sedentary behavior is a consequence of higher BMI.
It remains unclear exactly how physical activity, sedentary behavior (usually time spent sitting or lying, often in front of a screen), and obesity influence each other, and what role education plays in this relationship. Here, we use genetic information to study this relationship. We show that if you’re more physically active, you’re likely to be thinner. If your weight is higher, you tend to spend more time in front of the TV or computer. Additionally, getting more years of education leads to more physical activity, less screen time, and a lower weight later in life. The take-home messages are that being more physically active can prevent obesity; watching more TV is a result but not the cause of obesity; and education stimulates a healthier lifestyle later in life. These findings may help to guide public health messaging around healthy lifestyles.
© 2023. The Author(s).