Short-term weight change and the incidence of diabetes in midlife: results from the Australian Longitudinal Study on Women's Health.

OBJECTIVE Although there is consensus that excess adiposity is strongly associated with type 2 diabetes, its relationship with weight change is less clear. This study investigates the relative impact of BMI at baseline and short-term (2- or 3-year) weight changes on the incidence of diabetes. RESEARCH DESIGN AND METHODS Prospective data were collected from a population-based cohort of middle-aged women participating in the Australian Longitudinal Study on Women's Health (n = 7,239 for this report). To date, participants have completed four mailed surveys (S1, 1996; S2, 1998; S3, 2001; and S4, 2004). Generalized estimating equations were used to model binary repeated-measures data to assess the impact of BMI at S1 and weight change (S1 to S2; S2 to S3) on 3-year incidence of diabetes at S3 and S4, respectively, adjusting for sociodemographic and lifestyle factors. RESULTS BMI at S1 was strongly associated with the development of diabetes by S3 or S4. Compared with women who had a BMI <25 kg/m2, those with BMI > or =25 kg/m2 had higher incidence of diabetes (P < 0.0001), with odd ratios reaching 12.1 (95% CI 7.6-19.3) for women in the very obese group (BMI > or =35 kg/m2). There was no association between shorter-term weight gain or weight loss on first-reported diagnosis of diabetes (P = 0.08). CONCLUSIONS Because women's risk of developing type 2 diabetes in midlife is more closely related to their initial BMI (when aged 45-50 years) than to subsequent short-term weight change, public health initiatives should target the prevention of weight gain before and during early adulthood.