Shift work, shift change, and risk of death from heart disease at work

Some epidemiologic studies suggest workers who rotate shift are at increased risk of cardiovascular disease, but no studies have studied the effect of shift workers who do not rotate. To determine whether current shift or recent change in shift was a risk factor for ischemic heart disease, we conducted a nested case-control study of heart disease death at work within a cohort of 21,000 men working at four heavy equipment plants. We identified 163 men who died of ischemic heart disease at work or within 1 week of working, and compared them 781 controls who were working at the same age but did not die. Plant personnel records were used to determine duration of time on current shift. At the time of case death, 72% of study subjects were working on first shift, 22% on second, and 6% on third. The average time on shift without change was 9 years. There was little evidence of any difference in heart disease risk by current shift. There was some indication that recent change from afternoon or night shift to day shift had a protective effect initially, which decreased over time. On the other hand, no corresponding negative effect was found for a change from first to second/third shift, regardless of when the change took place. Our analyses were limited by the small number of workers on the third shift. We consider our analysis to be exploratory, and encourage more research on this topic in other working populations.