Background
Obesity is a risk factor for numerous chronic diseases and all-cause mortality. However, limited research on body mass index (BMI) and mortality has assessed patterns of BMI change across adulthood.
Methods
Group-based trajectories in BMI were estimated for 33,430 adults aged 40 to 70 years in the Melbourne Collaborative Cohort Study, using data collected on three occasions and recalled data for age 18 to 21 years. We used Cox regression to estimate hazard ratios (HR) of trajectories for all-cause mortality.
Results
We identified six BMI trajectories: lower-normal stable (TR1), higher-normal stable (TR2), normal to overweight (TR3), borderline obesity chronic (TR4), normal to class I obesity (TR5), and overweight to class II obesity (TR6). Compared with stable lower-normal BMI, chronic borderline obesity (TR4) and midlife obesity (TR5 and TR6) were associated with slightly higher mortality (HR=1.15, 1.01 to 1.30; HR=1.13, 1.02 to 1.24; HR=1.27, 1.09 to 1.48, respectively). In never-smokers, the HRs for TR4 to TR6 were higher than for all participants and the HRs for TR4 and TR6 were closer to each other.
Conclusion
Midlife obesity was associated with higher all-cause mortality even when BMI was normal in early adulthood, highlighting the importance of weight management throughout adulthood. Prolonged borderline obesity and changing from overweight to class II obesity in later life had similar associations with mortality. Therefore, policies and prevention programs should target obesity starting early in life if we are to mitigate the effects of current trends of increasing obesity in children, adolescents and young adults.