Previous research on the medical consequences of shift work has mainly been concerned with sleep disorders and gastrointestinal disturbances. Cardiovascular disease has not been clearly implicated. The objective of the present study was to investigate a possible association between shift work and Coronary Heart Disease (CHD), which is the most common cause of death in industrialized countries. Previous research is reviewed and criticized for using simple approaches with little ability to quantify exposure and to control for selection. Two longitudinal and two cross-sectional studies have been carried out. One study has measured incidence of CHD in 504 male day and shiftworkers from 1968 to 1982/83. The results indicate that shift work is associated with CHD. Our result has demonstrated a dose-response relationship between years of shift work and CHD. Our findings on increased risk of CHD in shift workers are consistent with recent epidemiological studies from Sweden which have used register data. The cross-sectional studies in which two different cohorts of male blue-collar workers were investigated did show a higher percentage of smokers among shift workers. In addition, the shift workers had higher serum concentrations of serum triglycerides. The difference in serum triglyceride levels between day and shift workers could not be explained by obesity, smoking or alcohol intake in the statistical analyses. These results suggest that the prevalence of risk factors for CHD is higher among shift workers. A prospective study of 25 male shift and day workers, who were followed for six months, indicated that the diet of shift workers might be responsible for changes in the ratio between apoB and apoA-1, a ratio which is related to risk of coronary disease. The analyses of spontaneous changes in the diet showed that the shift workers tended to decrease the intake of dietary fibre and increase the intake of sacharose. The change in the ratio between apoB and apoA-1 correlated inversely with the change in intake of dietary fibre. It is concluded that spontaneous changes in the diet of shift workers might be responsible for changes in serum lipoproteins. Three major disease pathways from shift work to CHD are proposed: (i) disturbed physiological rhythm and/or a collision between the circadian rhythm and myocardial performance, (ii) changes in behaviour, and (iii) disturbed sociotemporal rhythmicity, which might lead to distress reactions.
