Shift work, occupation and coronary heart disease over 6 years of follow-up in the Helsinki Heart Study

Objectives The risk of coronary heart disease (CHD) in shift work and the possible pathways for CHD in industrial workers were studied along with the importance of shift work as an occupational class gradient of CHD risk. Methods Data from a psychosocial questionnaire and on life-style factors, brood pressure, and serum lipid levels were used for a follow-up study of a cohort of 1806 workers. CHD was determined from official Finnish registers. Cox's proportional hazards models were used with different covariates to evaluate the relative risks associated with shift work. Results All the blue-collar workers smoked more and a had higher systolic blood pressure than the white-collar workers. Three-shift workers scored low for job-decision latitude on the Karasek job stress scales. There were no differences in the total cholesterol or high-density lipoprotein cholesterol levels. When all the shift workers were compared with all the day workers, the relative risk of CHD was 1.5 [95% confidence interval (95% CI) 1.1-2.1] when only age was adjusted for and 1.4 (95% CI 1.0-1.9) when life-style factors, brood pressure, and serum lipids were also adjusted for. The blue-collar day workers and 2-shift and 3-shift workers had relative risks of 1.3 (95% CI 0.8-2.0), 1.9 (95% CI 1.1-3.4), and 1.7 (95% CI 1.1-2.7), respectively, when compared with the white-collar day workers. Conclusions shift work is an important part of the occupational gradient in CHD risk among industrial workers; some evidence was found for the hypothesis that a direct stress-related mechanism explains part of the increased CHD risk.