Association between shift work and risk of prostate cancer: a systematic review and meta-analysis of observational studies.

Observational studies suggest that shift work may be associated with prostate cancer. However, the results are inconsistent. The objective of this study is to quantitatively assess the association between shift work and the risk of prostate cancer. Relevant studies were identified by a comprehensive search of the PubMed, Embase, Web of Science and China National Knowledge Infrastructure databases to September 2017. We also reviewed the reference lists from retrieved articles. Observational studies that reported relative risk (RR) with 95% confidence intervals (CIs) for the association between shift work and the risk of prostate cancer were included. Linear and non-linear dose-response meta-analyses were performed. Fifteen studies with 16 independent reports involving 2 546 822 individuals and 10 715 patients with prostate cancer were included. The pooled adjusted RR for the association between ever exposure to shift work and prostate cancer risk was 1.23 (95% CI, 1.08-1.41; P < 0.001). A non-linear association of prostate cancer risk with duration of shift work was identified (P for non-linearity = 0.001). Subgroup analysis demonstrated a higher pooled RR of prostate cancer for studies among Asian populations (RR = 1.98, 95% CI, 1.34-2.93; P = 0.618). A positive association was observed in rotating shift groups (RR = 1.10, 95% CI, 1.00-1.26; P = 0.156), but not in other shift groups. Integrated evidence from this meta-analysis suggests that shift work is significantly associated with an increased risk of prostate cancer, and a non-linear association between duration of shift work and prostate cancer was found.