Twenty years of socio-economic inequalities in type 2 diabetes mellitus prevalence in Spain, 1987-2006

Background: To analyse trends in socio-economic inequalities in the prevalence of diabetes among men and women aged epsilon 35 years in Spain during the period 1987-2006. Methods: We analysed trends in the age-standardized prevalence of self-reported diabetes and obesity in relation to level of education using data from the Spanish National Health Survey for the years 1987, 1993, 1995, 1997, 2001, 2003 and 2006 (86 345 individuals aged >= 35 years). To assess the relationship between education level and diabetes and obesity, we computed the Slope Index of Inequality and the Relative Index of Inequality (RII) for each year. Additional models were fit to take into account mediator variables in socio-economic position (SEP) diabetes inequalities. Results: The prevalence of self-reported diabetes was higher among persons of low educational level, increasing more rapidly over time among people with lower education level (5.0-12.6% in men, and 8.4-13.1% in women between 1987 and 2006) than among those with higher education level (6.3-8.7% in men and 3.8-4.0% in women). Relative inequalities showed a weak tendency to increase. In women, the RII of self-reported diabetes increased from 3.04 (1.95-4.74) in 1987 to 4.28 (2.98-6.13) in 2006, while in men were constant since 1993. Trends in SEP inequalities in diabetes prevalence were attenuated when mediator variables were taken into account in women but not in men. Conclusion: SEP inequalities in diabetes existed > 20 years ago and have increased, especially among women. These patterns may be explained by trends in health behaviours and obesity, but only to a limited extent