Life-Course Trajectories of Body Mass Index, Insulin Resistance, and Incident Diabetes in Chinese Adults.

Objective: This study aimed to explore the interplay between the life-course body mass index (BMI) trajectories and insulin resistance (IR) on incident diabetes.

Methods: This longitudinal cohort included 2,336 participants who had BMI repeatedly measured 3-8 times between 1989 and 2009, as well as glucose and insulin measured in 2009. BMI trajectories were identified using a latent class growth mixed model. The interplay between BMI trajectories and IR on diabetes was explored using the four-way effect decomposition method. Logistic regression and mediation models were used to estimate the interaction and mediation effects, respectively.

Results: Three distinct BMI trajectory groups were identified: low-stable ( n = 1,625), medium-increasing ( n = 613), and high-increasing ( n = 98). Both interaction and mediation effects of BMI trajectories and IR on incident diabetes were significant ( P < 0.05). The proportion of incident diabetes was higher in the IR-obesity than in the insulin-sensitivity (IS) obesity group (18.9% vs. 5.8%, P < 0.001). After adjusting for covariates, the odds ratios (95% confidence intervals) of the IR, IS-obesity, and IR-obesity groups vs. the normal group were 3.22 (2.05, 5.16), 2.05 (1.00, 3.97), and 7.98 (5.19, 12.62), respectively. IR mediated 10.7% of the total effect of BMI trajectories on incident diabetes ( P < 0.001).

Conclusion: We found strong interactions and weak mediation effects of IR on the relationship between life-course BMI trajectories and incident diabetes. IS-obesity is associated with a lower risk of incident diabetes than IR-obesity.