Body mass trajectories and mortality among older adults: a joint growth mixture-discrete-time survival analysis

The aim of this study was to investigate heterogeneity in body weight trajectories among older adults and their association with mortality risks.

Information on body mass index (BMI) and survival come from nine waves of the Health and Retirement Study, a 16-year survey of adults aged 51-61 at baseline (N = 9,703). We used a sex-stratified joint growth mixture-discrete time survival model to characterize BMI trajectory groups and their associated mortality.

Three distinct classes of BMI trajectories were identified: "stable overweight," "obese gaining," and "obese losing." Relative to the stable overweight class, which comprised about 90% of the sample, the obese gaining class had approximately 50% higher mortality risk; the highest mortality was found in the obese losing category (OR > 2.7, p < .001). The results were similar for men and women.

The findings highlight substantial heterogeneity in weight trajectories of older Americans, as well as large survival differentials across the classes. The direction of weight changes appears inextricably linked to the overall BMI level in terms of predicting older adults' longevity. Weight loss is associated with particularly high mortality risk even when the typical BMI change is from obesity to overweight.