Contribution of income and job strain to the association between education and cardiovascular disease in 1.6 million Danish employees

Abstract

Aims: We examined the extent to which associations between education and cardiovascular disease (CVD) morbidity and mortality are attributable to income and work stress.

Methods and results: We included all employed Danish residents aged 30-59 years in 2000. Cardiovascular disease morbidity analyses included 1 638 270 individuals, free of cardiometabolic disease (CVD or diabetes). Mortality analyses included 41 944 individuals with cardiometabolic disease. We assessed education and income annually from population registers and work stress, defined as job strain, with a job-exposure matrix. Outcomes were ascertained until 2014 from health registers and risk was estimated using Cox regression. During 10 957 399 (men) and 10 776 516 person-years (women), we identified 51 585 and 24 075 incident CVD cases, respectively. For men with low education, risk of CVD was 1.62 [95% confidence interval (CI) 1.58-1.66] before and 1.46 (95% CI 1.42-1.50) after adjustment for income and job strain (25% reduction). In women, estimates were 1.66 (95% CI 1.61-1.72) and 1.53 (95% CI 1.47-1.58) (21% reduction). Of individuals with cardiometabolic disease, 1736 men (362 234 person-years) and 341 women (179 402 person-years) died from CVD. Education predicted CVD mortality in both sexes. Estimates were reduced with 54% (men) and 33% (women) after adjustment for income and job strain.

Conclusion: Low education predicted incident CVD in initially healthy individuals and CVD mortality in individuals with prevalent cardiometabolic disease. In men with cardiometabolic disease, income and job strain explained half of the higher CVD mortality in the low education group. In healthy men and in women regardless of cardiometabolic disease, these factors explained 21-33% of the higher CVD morbidity and mortality.

Keywords: Cardiovascular disease; Cardiovascular mortality; Mechanisms; Nationwide study; Social determinants; Universal coverage.

Figure 1

Association between education and incident cardiovascular disease in men after 14-year follow-up. See Table 2 for an explanation of the models. CBD, cerebrovascular disease; CHD, coronary heart disease; CI, confidence interval; CVD, cardiovascular disease; HR, hazard ratio; PY, person-years.

Figure 2

Association between education and incident cardiovascular disease in women after 14-year follow-up. See Table 3 for an explanation of the models. CBD, cerebrovascular disease; CHD, coronary heart disease; CI, confidence interval; CVD, cardiovascular disease; HR, hazard ratio; PY, person-years.

Figure 3

Association between education and mortality in men after 14-year follow-up. See Table 4 for an explanation of the models. CI, confidence interval; CVD, cardiovascular disease; HR, hazard ratio; PY, person-years.

Figure 4

Association between education and mortality in women after 14-year follow-up. See Table 5 for an explanation of the models. CI, confidence interval; CVD, cardiovascular disease; HR, hazard ratio; PY, person-years.

Take home figure

Association between low compared to high education and cardiovascular disease and cardiovascular death after 14-year follow-up. Association between educational attainment and cardiovascular disease and cardiovascular death after 14-year follow-up in men and women without and with cardiometabolic disease with % excess risk explained by income and job strain. HR (95% CI) for low compared to high educational attainment adjusted for age, migration background, family type, and health services use in Step 1 and further adjusted for income and job strain in Step 2. CI, confidence interval; HR, hazard ratio.