Income and risk of ischaemic heart disease in men and women in a Nordic welfare country

Background The inverse relation between ischaemic heart disease (IHD) and income is well known among men, but it remains to be clarified whether the relationship between social gradient and IHD is similar for men and women. The present study explores the associations between income and IHD in men and women in a Nordic country. Methods We used data from two prospective population studies conducted in Copenhagen. A total of 22 782 subjects, 54% women, with initial examination between 1964 and 1992 were followed until 1996 for hospital admission or death from IHD. We performed survival analyses, taking traditional cardiovascular risk factors into account, and estimated IHD-free life expectancy by household income in men and women. Results During follow-up, 1803 men and 1258 women experienced an event of IHD (21% fatal). The hazards by deciles of income showed a non-linear graded inverse effect of income, with a large group of middle-income in which income was not associated with risk of IHD. The hazard ratio for highest versus lowest deciles was 0.53 (95% CI: 0.44-0.65). The association was attenuated by adjustment for risk factors, but remained statistically significant. The associations were similar for both sexes. Median IHD-free life expectancy for low-income versus high-income groups was reduced by 9.4 and 7.0 years in men and women, respectively. Conclusions The effect of household income on risk of IHD was graded and similar for men and women. The difference between high and low income, regarding IHD-free life expectancy, was considerable.