Shift Work and Prostate Cancer Incidence in Industrial Workers A Historical Cohort Study in a German Chemical Company

Background: There is inconsistent evidence for a possible carcinogenic effect of shift work. In particular, little is known about the putative association of shift work with prostate cancer. Method: We studied a cohort of 27 828 male industrial production workers residing in the German federal state of Rhineland-Palatinate who worked for at least one year in a chemical company in the period 1995-2005. We obtained data on shift work and potential confounders including age, occupational task, and duration of employment from personnel files and from the records of the occupational health service. New cases of cancer in the period 2000-2009 were ascertained from the state cancer registry. Differences in risk between shift workers and daytime workers were analyzed with Cox regression, stratified by stage of cancer, and adjusted for potential confounding effects. Results: There were 146 new cases of prostate cancer in 12 609 rotating shift workers and 191 in 15 219 daytime workers. The median year of birth was 1960 in the first group and 1959 in the second. The shift workers did not have an elevated hazard ratio for prostate cancer in comparison to the daytime workers (HR = 0.93, 95% confidence interval [CI] 0.73-1.18). Some differences were seen depending on tumor stage. Both groups of workers had a higher incidence of prostate carcinoma than the general population (standardized incidence rate [SIR] = 1.44, 95% CI 1.22-1.70 for daytime workers; SIR = 1.51, 95% CI 1.30-1.74 for shift workers). Conclusion: In this well-documented, large-scale cohort study, the incidence of prostate cancer among shift workers did not differ from that among daytime workers. In the authors' opinion, further follow-up of this relatively young cohort is required.