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/m(2)) or obese (BMI >= 30 kg/m(2)) 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.