Duration of obesity and overweight and risk of type 2 diabetes among US women

Objective The purpose of this study was to examine the association between duration of adiposity and risk of type 2 diabetes (T2D) in US women. Methods We prospectively followed 61,821 participants from the Nurses' Health Study (1984-2008) and 63,653 participants from Nurses' Health Study II (1991-2011). Participants were considered overweight (BMI 25-30 kg/m2) or obese (BMI >= 30 kg/m2) if their BMI was above the cutoffs for two successive assessments. We used time-dependent Cox proportional hazard models to assess associations between excess weight duration and T2D risk. Results In pooled multivariable analyses of the two cohorts, each two extra years of being overweight was associated with 9% (RR=1.09, 95% CI 1.08 - 1.09) increased risk of developing T2D. For each 2-year increment in obesity duration, the risk of T2D was increased by 14% (RR=1.14, 95% CI 1.14 - 1.15). Adjustment for current BMI greatly attenuated the association for obesity duration (RR =1.02, 95% CI 1.01 - 1.03), although the attenuation was less for overweight duration (RR =1.04, 95% CI 1.04 - 1.05). Conclusions Both overweight and obesity duration were associated with a significantly higher risk of T2D, and these associations were mainly explained by current BMI, especially for obesity duration.