Life course analysis on income and incident AMI: a Danish register-based cohort study

BACKGROUND: Social inequality in ischaemic heart disease has been related to socioeconomic position in childhood, early adulthood and late adulthood. However, the impact of relative level of accumulated income periods across adult life course and the potential gender and age differences have not been investigated. The aim was to investigate the association between relative level of accumulated income across the life course and acute myocardial infarction (AMI) from age 60+ years and to study if the associations differ by gender and in different age groups (30-39 years, 40-49 years and 50-59 years). METHODS: All Danes born 1935-1954 (N=1 235 139) were followed up in registers for incident AMI (42 669 cases). The accumulated proportional deviation from median equivalised income (APDMEI) for each gender/age/calendar year strata was constructed and divided in quartiles. The associations were analysed by means of Cox's proportional hazard models. RESULTS: Among men, those in the lowest APDMEI quartile had an HR 1.40 (1.35-1.45) of AMI compared with the highest quartile. Those in the second and third highest quartiles had HR of 1.24 (1.20-1.28) and 1.14 (1.10-1.18), respectively. Among women, the lowest quartile had an HR of 1.78 (1.69-1.88), the second 1.45 (1.37-1.53) and the third 1.19 (1.13-1.26). The social gradient was similar across the different age groups. CONCLUSION: The risk of AMI increased with lower levels of relative accumulated income across the life course. While men generally had a higher risk of AMI, the social gradient was steeper in women. There was no indication of a specific sensitive age period for exposure to relative level of accumulated income.