Background Increasing number of observational studies suggests that shift work is associated with prostate cancer. However, the results remain controversial. We conducted a meta-analysis including either studies that directly assessed shift work or those that assessed shift work-related occupations to clarify the association.

Methods Relevant studies were identified by searching 3 databases through February 2016 and reference lists of the retrieved articles were also reviewed. We included observational studies that reported risk estimate with 95% CIs for the association between shift work and the risk of prostate cancer. Random-effects models were used to calculate the pooled risk estimates.

Results A total of 25 studies with 712,296 participants involving 15571 prostate cancer cases were included. A significantly increased risk of prostate cancer was observed among either studies directly assessing shift work exposure (OR = 1.22, 95% CI: 1.08 to 1.36) or those assessing shift work-related employments (OR = 1.16, 95% CI: 1.09 to 1.23) with substantial heterogeneity. The association remained significant in most subgroup and sensitivity analyses. Dose-response analysis suggested that the risk of prostate cancer increased by 2.8% (95% CI: 0.4 to 5.5, p = 0.023) for every 5-year increase of exposure to shift work. The percent of prostate cancer deaths attributable to shift work was approximately 3.5% and 4.4% in the US and Europe respectively, equal to 4906 deaths per year in total.

Conclusion Shift work is associated with an increased risk of prostate cancer. Further studies assessing different domains of shift work are warranted to confirm our findings and clarify the underlying mechanisms.