Adiposity Compared With Physical Inactivity and Risk of Type 2 Diabetes in Women

OBJECTIVE—The relative contribution of adiposity and physical inactivity to the risk of developing type 2 diabetes remains controversial. RESEARCH DESIGN AND METHODS—We prospectively examined the individual and joint association of obesity and physical activity with the development of type 2 diabetes in 68,907 female nurses who had no history of diabetes, cardiovascular disease, or cancer at baseline. Adiposity was measured by BMI and waist circumference. Physical activity was assessed through average hours of moderate or vigorous exercise and computation of an MET score. RESULTS—We documented 4,030 incident cases of type 2 diabetes during 16 years of follow-up (from 1986 to 2002). In a multivariate model including age, smoking, and other diabetes risk factors, risk of type 2 diabetes increased progressively with increasing BMI (P < 0.001) and waist circumference (P < 0.001) and with decreasing physical activity levels (P < 0.001). In joint analyses of BMI and physical activity, using women who had a healthy weight (BMI <25 kg/m2) and were physically active (exercise ≥21.8 MET h/week) as the reference group, the relative risks of type 2 diabetes were 16.75 (95% CI 13.99–20.04) for women who were obese (BMI ≥30 kg/m2) and inactive (exercise <2.1 MET h/week), 10.74 (8.74–13.18) for women who were active but obese, and 2.08 (1.66–2.61) for women who were lean but inactive. In combined analyses of waist circumference and physical activity, both variables were significant predictors of type 2 diabetes, but the association for waist circumference was substantially stronger than that for physical inactivity. CONCLUSIONS—Obesity and physical inactivity independently contribute to the development of type 2 diabetes; however, the magnitude of risk contributed by obesity is much greater than that imparted by lack of physical activity.