Variation in the relationship between BMI and survival by socioeconomic status in Great Britain

•We model the relationship between BMI and survival by SES using the “Pathways to health” framework.•There is evidence of interactions between BMI and age and BMI and SES in women, but not in men.•In 50 year old men obesity reduces survival by 3.2 years compared with normal weight.•In 50 year old women analogous figures are 9.7 years and 3.1 years in the lowest and highest SES groups, respectively.

We investigate the relationship between obesity and survival, and the extent to which this relationship varies by socioeconomic status (SES). The underlying model is based on the “Pathways to health” framework in which SES affects health by modifying the relationship between lifestyles and health. We use data from the British Health and Lifestyle Survey (1984-1985) and the longitudinal follow-up in June 2009, and run parametric Gompertz survival models to investigate the association between obesity and survival, also accounting for interactions between obesity and both age and SES. Generally we find that obesity is negatively associated with survival, and that SES is positively associated with survival, in both men and women. The interactions between obesity and SES predict survival among women but not among men. Obesity compared with normal weight is associated with a reduction in survival of 3.3, 3.2 and 2.8 years in men aged 40, 50 and 60 years, respectively. Corresponding numbers among women in the lowest SES group are 13.1, 9.7 and 6.1 years, respectively; in the highest SES group they are 6.2, 3.1 and 0.1 years, respectively, a difference of approximately 6 years between the highest and lowest SES groups.