Shift work and risk of cardiovascular disease morbidity and mortality: A dose-response meta-analysis of cohort studies

Background: Previous studies have suggested that shift work is associated with a higher risk of cardiovascular disease. However, the quantitative dose-response relationship between duration of shift work and cardiovascular disease risk is still unknown. We aimed to evaluate the dose-response association between duration of shift work and risk of cardiovascular disease morbidity and mortality. Design: A systematic review and meta-analysis. Methods: PubMed and Embase were searched from inception to I December 2017. Prospective cohort studies that reported the associations between duration of shift work and cardiovascular disease risk with at least three categories were included. Data were pooled by using fixed or random effect models. The continuous dose-response associations were assessed by using fixed effect restricted cubic splines with four knots. Results: Five prospective cohort studies with 10 reports were included. No evidence of a curvilinear association was observed between duration of shift work and risk of cardiovascular disease, similar findings were observed in cardiovascular disease morbidity and mortality. The summary relative risk (RR) of an increase of 5 years of shift work was 1.05 (1.04-1.07) with moderate heterogeneity (P=0.142, I-2 = 33.2%) for cardiovascular disease, 1.06 (1.04-1.08) with low heterogeneity (P= 0.279, I-2 =- 21.7%) for cardiovascular disease morbidity, and 1.04 (1.02-1.06) with moderate heterogeneity (P = 0.135, I-2 = 38.5%) for cardiovascular disease mortality, respectively. Conclusions: Shift work could probably increase the risk of cardiovascular disease and cardiovascular disease mortality in a dose-response way. These findings could have implications for guideline recommendations regarding the risk related to shift schedules.