Socioeconomic trajectories of body mass index and waist circumference: results from the English Longitudinal Study of Ageing

OBJECTIVES: To explore age trajectories of body mass index (BMI) and waist circumference (WC) and to examine whether these trajectories varied by wealth. DESIGN: Nationally representative prospective cohort study. SETTING: Observational study of people living in England. PARTICIPANTS: 7416 participants aged 52 and over of the English Longitudinal Study of Ageing (2004–2012). PRIMARY OUTCOME MEASURES: BMI and WC assessed objectively by a trained nurse. MAIN EXPOSURE MEASURE: Total non-pension household wealth quintiles defined as financial wealth, physical wealth (such as business wealth, land or jewels) and housing wealth (primary and secondary residential housing wealth), minus debts. RESULTS: Using latent growth curve models, we showed that BMI increased by 0.03 kg/m(2) (95% CI 0.02 to 0.04, p<0.001) per year and WC by 0.18 cm (95% CI 0.15 to 0.22, p<0.001). Age (linear and quadratic) showed a negative association with BMI and WC baseline and rates of change, indicating that older individuals had smaller body sizes and that the positive rates of change flattened to eventually become negative. The decline occurred around the age of 71 years for BMI and 80 years for WC. Poorest wealth was significantly related to higher baseline levels of BMI (1.97 kg/m(2) 95% CI 0.99 to 1.55, p<0.001) and WC (4.66 cm 95% CI 3.68 to 2.40, p<0.001). However, no significant difference was found in the rate of change of BMI and WC by wealth, meaning that the age trajectories of BMI and WC were parallel across wealth categories and that the socioeconomic gap did not close at older ages. CONCLUSIONS: Older English adults showed an increase in BMI and WC over time but this trend reversed at older old age to display a sharp decrease. At any given age wealthier people had more favourable BMI and WC profile.