Body mass index and waist circumference trajectories among midlife women in the United States and their association with incident diabetes: The Study of Women’s Health Across the Nation

Background This study aimed to identify the trajectories of BMI and waist circumference (WC) in middle-aged women in the U.S. and examine their association with incident diabetes. Methods We used secondary data from the longitudinal Study of Women’s Health Across the Nation over 10 annual visits (1996–2008). Latent class growth modeling was used to identify BMI and WC trajectory groups during visits 1–5. Cox proportional hazards regression models were used to estimate the hazard ratios (HRs) for diabetes during visits 6–10. Results Among 1,406 women, 90 (6.4%) developed diabetes. Four BMI trajectory groups were identified: high increasing (19.5%), low stable (37.4%), medium increasing (34.8%), and very high increasing (8.3%) with HRs for diabetes of 3.83 (95% CI: 1.76, 8.31) in the medium increasing, 6.97 (95% CI: 3.00, 16.16) in high increasing, and 14.22 (5.92, 34.17) in very high increasing trajectory groups. Four WC trajectory groups were identified: increasing (35.9%), normal increasing (38.4%), high increasing (18.7%), and very high stable (6.9%); HRs for diabetes were 2.26 (95% CI: 1.06, 4.85) in increasing, 8.12 (95% CI: 3.64, 18.11) in high increasing, and 11.30 (95% CI: 4.69, 27.25) in very high stable groups. Four multi-trajectories of BMI and WC were identified: group 1 (34.5%, high increasing BMI and increasing WC), group 2 (33.1%, low stable BMI and normal increasing WC), group 3 (22.1%, medium increasing BMI and high increasing WC), and group 4 (10.3%, very high increasing BMI and very high increasing WC) with a higher rates of diabetes in groups 1, 3, and 4. Conclusions Middle-aged women followed distinct BMI and WC trajectory groups that were associated with incident diabetes. Public health interventions on weight management could help reduce the burden of diabetes in this population.