Previous reviews have suggested that shift work is associated with an increased risk of diabetes mellitus (DM); however, the results should be interpreted with caution due to differences in study designs and non-comprehensive literature searches. In addition, the quantitative dose-response relationship between years of shift work and DM risk is still unknown. We aimed to conduct an updated meta-analysis with cohort studies and to evaluate the relationship between the duration of shift work and the risk of DM in a dose-dependent manner. The PubMed and Web of Science databases were searched through 15 August 2019, and multivariate-adjusted relative risks (RRs) were pooled using random-effects models. Restricted cubic spline analysis with three knots was used to explore the relationship of years of shift work and risk of DM. Twelve cohort studies with 28 independent reports involving 244,266 participants and 15,906 DM cases were included. The summarized adjusted RR for the relationship between shift work and DM risk was 1.14 (95% CI 1.10 to 1.19; I2 = 38.9%, P = 0.028). The summary RR of a 5-year increase in shift work was 1.07 (95% CI 1.04 to 1.09), without heterogeneity (I2= 0.0%, P = 0.829) for the female population. Shift work is associated with an increased risk of DM, and a strong and highly significant linear dose-response relationship between the duration of shift work and the risk of DM in women was observed. Further studies are needed to confirm the results, establish causality and elucidate the underlying mechanisms.
Keywords: Cohort; Diabetes mellitus; Dose-response relationship; Meta-analysis; Shift work.