Shift work and the risk of ischemic heart disease - a systematic review of the epidemiologic evidence

Objective The objective of this review was to evaluate the epidemiologic evidence for a causal relation between shift work and ischemic heart disease. Methods We conducted a systematic search until the end of March 2008 for studies providing information on the relative risk of ischemic heart disease in relation to shift work. The quality of included papers was evaluated with respect to design, exposure and outcome information, bias, and exposure response assessment. Results Of the 16 studies examined, relevant information was retrieved from 14. Seven of these analyzed fatal events, six combined fatal and non-fatal events, while one study reported separately on both types of events. Relative risks ranged from 0.6-1.4 in 12 papers while two papers reported relative risks around 2.0. Most studies based on fatal events showed no or weak associations while studies that combined fatal and non-fatal events showed modest positive associations. In a majority of studies, we could not reasonably rule out negative or positive bias due to the quality of outcome or exposure information, or confounder control. Five studies used years in shift work for exposure response analysis and no consistent pattern were seen. Conclusion There is Limited epidemiologic evidence for a causal relation between shift work and ischemic heart disease.