Socioeconomic status and ischaemic heart disease mortality in middle-aged men: importance of the duration of follow-up. The Copenhagen Male Study

Objectives The predictive value of some risk factors may diminish with incr easing duration of follow-up. This study was performed to elucidate the rol e of socioeconomic status as a risk factor for ischaemic heart disease (MD) mortality in middle-aged men, testing the hypothesis that the role of medi ators of the association of socioeconomic Status with risk of IHD would dim inish with increasing length of follow-up. Methods A cohort of 5249 men aged 40-59 was established in 1971. Baseline d ata on social class and other confounder variables were collected, and the cohort was followed through registers for 8, 15, and 22 years. In all, 5028 without a history of myocardial infarction or angina pectoris were include d in the follow-up. Four factors associated with either occupation or lifes tyle were strong mediators of the association found between social class an d risk of fatal MD, and were more common in the lower social classes (class es IV and V): occasional demand for vigorous activity at work, low leisure time physical activity level, high alcohol consumption, and smoking. Results After the first 8 years, 78 men had died due to IHD, after 15 years : 222, and after 22 years: 411. Compared with social classes I, II, and m, the age-adjusted relative risk (RR) with 95% CI for classes IV and V was 1. 69, P < 0.05 after the first 8 years; adjusted for the above potential risk factors the RR dropped to 1.09, P = NS. Corresponding RR after 15 years we re 1.67, P < 0.001 and 1.33, P = NS; and after 22 years, 1.59, P < 0.001 an d 1.36, P < 0.05, Conclusions Risk factors with an uneven social distribution related to occu pation and lifestyle were strong mediators of the association of socioecono mic status with risk of IHD. A quite strong explanatory potential persisted but diminished with length of follow-up.