Examining the association between socioeconomic position and body mass index in 1978 and 2005 among Canadian working-age women and men

We examined the association between socioeconomic position (SEP) and body mass index (BMI) among Canadian men and women in 1978 and 2005. We examined both the average SEP-BMI association, and variation in this association across the distribution of BMI. We analysed data from two nationally representative surveys containing measured height and weight data: the Canada Health Survey (1978) and the Canadian Community Health Survey (2005). Ordinary least squares and quantile regression were used to examine average and distributional SEP-BMI associations, respectively, for each survey. Education was inversely associated with BMI for men and women at both time points, and there was no evidence of narrowing between 1978 and 2005. This association was stronger for women than men, and was particularly strong for heavier women. Education and income related differently to BMI. The SEP-BMI association in Canada is complex, showing variation by gender, by aspect of SEP, across the BMI distribution, and at different time points. The association departs from the more consistent social gradient in health, thereby challenging our view of BMI as a typical health issue.