Do physical and chemical working conditions explain the association of social class with ischaemic heart disease? Original Research Article

The aim of this study was to examine whether physical and chemical working conditions explain the association of social class with ischaemic heart disease (IHD). We investigated the issue in a cohort of 2974 males aged 53–75 years (mean 63) free from overt cardiovascular disease. Potential confounders included were: alcohol consumption, physical activity, tobacco smoking, serum cotinine, serum lipids, serum selenium, body mass index, blood pressure, hypertension, social class, and retirement status. During the follow-up period (1985–1986 to 31 December 1991), 184 men (6.2%) had a first IHD event; 44 events were fatal. Compared to higher social classes (classes I, II and III), lower classes (classes IV and V) had a significantly increased risk of IHD (P < 0.05); the age-adjusted relative risk (RR) with 95% confidence limits was 1.44 (1.06–1.95), P = 0.02. Men who had been occupationally long-term exposed (≥5 years) to either soldering fumes or organic solvents had a significantly higher risk of IHD than unexposed: RRs were 2.1 and 1.7, respectively. After adjustment for all the above potential confounders and including also these two occupational factors, the RR of low social classes was reduced to a non-significant 1.24 (0.87–1.76), P = 0.24 i.e. by 45%. Adjusting for nonoccupational factors only reduced the RR from 1.44 to 1.38 (1.0–1.90), P = 0.05 i.e. by about 14%. Assuming that the association of soldering fumes and organic solvents with risk of IHD was causal, it was estimated that 16% of IHD cases in low social class could be ascribed to these exposures. Based on our results we hypothesize that social differences in exposure to soldering fumes and organic solvents are responsible for some of the increased risk of IHD in low social classes.