A new meta-analysis confirms that shift workers have increased risks for developing prostate cancer (PCa) and provides some additional insight.

Zuxun Lu, MD, of Huazhong University of Science and Technology in China, and his peers reviewed 15 studies published 2002 to 2017 including 2,546,822 men, of whom 10,715 developed PCa. According to pooled results published online in Carcinogenesis, shift workers had a significant 23% higher risk of PCa than those who had never performed shift work. The investigators found a nonlinear relationship between longer shift duration and greater PCa risk. Results were adjusted for age, smoking status, education, body mass index, physical activity, and area of residence.

Included studies were conducted in Europe, the United States, Canada, Japan, and China. A subgroup analysis found that Asian shift workers had nearly twice the risk of PCa compared with those from Western countries.

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Investigators categorized shift work as rotating, night, evening, or mixed. Rotating shift schedules – which might include a day shift followed by a night shift, for example – had the most association with PCa risk. The investigators explained that rotating schedules force shift workers to adjust their body functions to their on-duty periods, thereby disrupting their sleep pattern.

Possible biologic mechanisms linking shift work in general to PCa include disruption of circadian rhythms, decreased melatonin (a hormone that has antioxidant, anti-mitosis, anti-angiogenesis, and immune effects that might protect from cancer), and impaired vitamin D synthesis due to reduced sunlight exposure.

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Gan Y, Li L, Zhang L, et al. Association between shift work and risk of prostate cancer: a systematic review and meta-analysis of observational studies.  Carcinogenesis. Epub December 2017.