Does psychosocial stress explain socioeconomic inequities in 9-year weight gain among young women?

OBJECTIVE: This study investigated the contribution of psychosocial stress to mediating inequities in weight gain by educational status in a large cohort of young Australian women over a 9-year follow-up. METHODS: This observational cohort study used survey data drawn from 4,806 women, aged 22 to 27 years at baseline (2000), participating in the Australian Longitudinal Study on Women's Health, who reported their education level (2000), perceived stress (2003), and weight (2003 and 2012). Using a causal inference framework based on counterfactuals for mediation analysis, we fitted linear or logistic regression models to examine the total effect, decomposed into natural direct and indirect effects via perceived stress, of education level (highest qualification completed: up to year 12/trade or diploma vs. university) on weight change. RESULTS: Women with lower education gained more weight over 9 years (6.1 kg, standard deviation [SD] 9.5) than women with higher education (3.8 kg, SD 7.7; P < 0.0001) and were more likely to be very or extremely stressed. The higher weight gain associated with low education was not mediated through perceived stress (per SD increase, percent mediated: 1.0%). CONCLUSIONS: Education-based inequities in weight gain over time were not attributable to greater psychosocial stress among women with lower education levels.