OBJECTIVES The study investigated long-term effects of carbon monoxide (CO) exposure on foundry workers' morbidity and mortality from cardiovascular diseases.

METHODS The study population comprised a cohort of 2857 men hired in 1950--1972 by 20 Finnish foundries and also 931 men who were still active in 1972, exposed for at least 4.2 years, took part in a health examination in 1973; 653 of the 931 had also been members of the cohort. These groups were followed to the end of 1987.

RESULTS The age-standardized incidence density rate (ID/1000 person-years) for compensated medication for hypertension was 4.7 for the unexposed workers and 9.4 for those exposed [rate ratio (RR) 2.0, 95% confidence interval (95% CI) 1.28--2.92]; for the iron foundry workers the rates were 4.7 and 9.9 (RR 2.1, 95% CI 1.24--3.38), respectively. During 1950--1987, 255 cardiovascular deaths were observed (284 expected according to national rates). The observed number of deaths due to ischemic heart disease was 183 (203 expected). The iron foundry workers' mortality rate for cardiovascular deaths was 99% of the national expected value. No remarkable differences were found between the CO-exposure categories. For the health-examination group, the age-standardized incidence rate for compensated medication for hypertension was 9.1 for the unexposed nonsmokers and 21.4 for the exposed smokers (RR 2.3, 95% CI 0.97-6.35); the difference originated among the iron foundry workers, for whom the rates were 8.1 and 24.0 (RR 3.0, 95% CI 0.96--9.78), respectively. The age-standardized mortality rate (ID/1000 person-years) was 2.7 for nonsmokers with no or slight CO exposure and 9.2 for exposed smokers (95% CI 1.13--12.11). This difference was mainly caused by ischemic heart disease.

CONCLUSIONS The results indicate that CO exposure increases the risk of cardiovascular morbidity and mortality.