Long-term effect of occupational noise on the risk of coronary heart disease

Objectives The aim of the study was to investigate the short- and long-term effects of occupational exposure to continuous and impulse ribise on the risk of CHD. Methods The effect of noise on CHD was studied among 6005 Finnish middle-aged industrially employed men (part of the screeners in the Helsinki Heart Study) in a prospective 18-year follow-up study. The CHD end points (codes 410-414 in the ninth revision of the International Classification of Diseases and codes 120-125 in the tenth revision) were obtained from official Finnish registers. The Finnish job-exposure matrix FINJEM provided estimates of the proportion of exposed persons and the mean level of exposure among those exposed by occupation. The relative risks (RR) of CHD and the 95% confidence intervals (95% CI) for noise exposure were calculated from Cox's proportional hazard models with adjustment for some other risk factors of CHD. Results The short-term (9-year follow-up) relative risk of CHD for the combined noise (continuous noise exceeding 80 decibels and impulse noise) was 1.38 (95% CI 1.04-1.82), and the long-term (18-year follow-up) RR was 1.54 (95% CI 1.28-1.86). For blue-collar workers the corresponding estimates were 1.11 (95% CI 0.82-1.51) and 1.29 (95% CI 1.05-1.57). Adjustment for other relevant risk factors did not materially change the results. Conclusions In our long-term follow-up of industrially employed men, exposure to noise, especially to impulse noise, was associated with a moderate, but statistically significant increase in CHD risk that persisted even after the workers had passed the age of retirement.