Successful Aging and Obesity: Social and Developmental Heterogeneity in Trajectories of Body Weight from Middle to Older Age

Abstract

Obesity is increasingly prevalent among older adults, yet little is known about the distribution of long-term trajectories of body-weight in this age group. The three essays included in this dissertation aim to depict the trajectories of body-mass index (BMI) from middle to old age and to examine social and behavioral variations in these trajectories. Eight waves (1992-2006) of the Health and Retirement Study involving a nationally representative cohort of Americans aged 51 to 61 years at baseline were used. Changes in BMI were analyzed using alternatively hierarchical linear modeling or semiparametric mixture modeling, with adjustment for time-constant and time-varying covariates.

First study finds that over 14 years, respondents followed a linearly increasing BMI trajectory. Compared with Caucasians, African- Americans had higher BMI levels, while Hispanics had similar BMI levels, but lower rates of increase over time. Higher education predicted lower BMI levels and was not associated with the rate of change. Older age-at-baseline predicted lower BMI levels and lower rates of increase. No gender differences were found. The second study shows that smoking and vigorous physical activity (user status and initiation) were associated with significantly lower BMI trajectories over time. Cessation of smoking and physical activity resulted in higher BMI trajectories over time. The weight-gaining effect of smoking cessation increased during the study period, while the strength of association between BMI trajectories and PA or alcohol use were constant. In the third study, five distinct BMI trajectories are identified, differing primarily in their intercept: normal BMI trajectory (19.9% of sample), overweight (43.8%), borderline-obese (25.4%), obese (8.9%), and morbidly-obese (2.1%). Each trajectory showed an upward trend over the study period, although the rate-of-increase varied between trajectories. Compared with Whites, Blacks and Hispanics had greater probabilities of membership in the higher BMI trajectory groups. Females had approximately half the risk of following the overweight and obese BMI trajectories compared with males. In conclusion, significant racial/ethnic, gender and educational heterogeneity in BMI trajectories exists in older adults. Health behaviors provide beneficial modifications in BMI trajectories. Tailoring of public health and clinical interventions to trajectory group characteristics may reduce obesity-related health disparities in aging.