Researchers have found that a higher body mass index (BMI) has a stronger association with development of diabetes than does physical inactivity, according to a study in the September 8 issue of JAMA.
Amy R. Weinstein, M.D., M.P.H., formerly of Brigham and Women’s Hospital, Boston, and colleagues investigated the combined relationship of BMI and physical activity with diabetes to understand whether increasing physical activity levels reduces the elevated risk of diabetes from obesity. The study included 37,878 participants from the Women’s Health Study, an ongoing clinical trial. The participants were free of cardiovascular disease, cancer, and diabetes at the beginning of the study, and follow-up averaged about 7 years. Weight, height, and recreational activities were reported at study entry. Normal weight was defined as a BMI of less than 25; overweight, 25 to less than 30; and obese, 30 or higher. A 5’4” woman would have a BMI of 25 if she weighed 145 lbs.; a BMI of 30 if she weighed 174 lbs. Active was defined as expending more than 1,000 kilocalories on recreational activities per week.
The researchers found that individually, BMI and physical activity were significant predictors of incident diabetes. Compared with normal-weight individuals, overweight individuals had a 3.2 times increased risk for diabetes; obese individuals, a 9.1 times increased risk. For overall activity (kilocalories expended per week), compared with the least active first quartile, a decreased risk of diabetes in the other quartiles ranged from 9 percent to 18 percent.
“We observed a modest reduction in the risk of diabetes with increasing physical activity level compared with a large increase in the risk with increasing BMI,” the authors write. “These findings underscore the critical importance of adiposity [level of fat content] as a determinant of type 2 diabetes. Because physical activity is a significant individual predictor and has a beneficial effect on BMI, it remains an important intervention for diabetes prevention. Our study suggests that to further reduce the risk of diabetes with physical activity, it should be performed in conjunction with achieving weight loss. By furthering our understanding of the relative influence of BMI and activity on diabetes, we may improve our ability to risk stratify patients and in turn may reduce the incidence of diabetes,” they write.