SHIFT WORK, SHIFT CHANGE, AND RISK OF DEATH FROM HEART-DISEASE AT WORK

Some epidemiologic studies suggest workers who rotate shift are at inc reased risk of cardiovascular disease, but no studies have studied the effect of shift for workers who do not rotate. To determine whether c urrent shift or recent change in shift was a risk factor for ishemic h eart disease, we conducted a nested case-control study of heart diseas e death at work within a cohort of 21,000 men working at four heavy eq uipment plants. We identified 163 men who died of ischemic heart disea se at work of within 1 week of working, and compared them to 781 contr ols 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 t he time of case death, 72% of study subjects were working on first shi ft, 22% on second, and 6% on third. The average time on shift without shift 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 protec tive effect initially, which decreased over time. On the other hand, n o corresponding negative effect was found for a change from first to s econd/third shift, regardless of when the change took place. Our analy ses were limited by the small number of workers on the third shift. We consider our analyses to be exploratory, and encourage more research on this topic in other working populations. (C) 1996 Wiley-Liss, Inc.