Social mobility and adiposity in a recently transitioned population of Hong Kong: evidence from the FAMILY cohort

Abstract

INTRODUCTION: While social mobility, particularly downward movement in social hierarchy, has been associated with adiposity in long-term industrialized populations, evidence from recently transitioned populations is inconsistent. In a recently developed population from Hong Kong we examined the association of social mobility, assessed using life course socio-economic position (SEP) trajectories, with general adiposity, proxied by body mass index (BMI) and central adiposity, proxied by waist circumference and waist-hip ratio (WHR). METHODS: In a cross-sectional study of 2,965 adults from 1,554 households, aged 20-80 years from the population-based FAMILY Cohort (Wave 2; 2012-13), we used multilevel linear regression models, adjusted for age, smoking status, use of alcohol, physical activity and family functioning, to assess the association of SEP trajectories with BMI, waist circumference and WHR using four combinations of low and high SEP in childhood (fathers’ occupation at age 10 years) and adulthood (highest attained education). Multilevel models account for the hierarchical structure of our data, where individuals are nested within households, allowing for household level variation in the outcomes. We assessed whether the associations varied by sex or age from the heterogeneity across strata and the significance of the relevant interaction term in an adjusted model including interactions of sex or age. RESULTS: Association of life course SEP with adiposity varied by sex (p-value <0.01). Compared to men with consistently low SEP, upwardly mobile men had higher BMI (0.82, 95% confidence interval (CI) 0.15 to 1.49) as did men with consistently high SEP, (0.83, 95% CI 0.20 to 1.45), who also had larger waist circumference (1.99 centimetre (cm), 95% CI 0.40 to 3.50). In women, upward social mobility was negatively associated with adiposity; women with consistently high SEP had the lowest WHR (-0.02, 95% CI -0.03 to -0.01) and waist circumference (-2.44 cm, 95% CI -3.87 to -1.00). CONCLUSIONS: This study shows that social mobility and social disadvantage have sex-specific associations with particularly central adiposity in the recently transitioned population of Hong Kong. Accumulation of disadvantage across the life course was associated with central adiposity in women but not men. Exposures during puberty could be a mechanism driving such sex-specific associations.