The results of a study published in the American Journal of Epidemiology suggest there is a significant association between rotating-shift work and prostate cancer.

“Shift workers are known to be a high-risk population for…some cancers,” such as breast cancer and colorectal cancer, Dr. Tatsuhiko Kubo, of the University of Occupational and Environmental Health, Kitakyushu, Japan, and colleagues write.

The researchers looked for a link between shift work and the incidence of prostate cancer among 14,052 male workers enrolled in the Japan Collaborative Cohort Study for Evaluation of Cancer Risk. A survey on lifestyle factors was conducted between 1988 and 1990.

The subjects were asked what their most common work schedule was: day work, rotating-shift work or night work. Overall, 11,269 (80.2 percent) were day workers, 982 (7.0 percent) were night workers, and 1801 (12.8 percent) worked a rotating-shift.

Thirty-one cases of prostate cancer were reported over an average follow-up period of 8 years.

When the data were adjusted for the effect of age, the researchers noted a three-fold increase in the risk of prostate cancer among the rotating-shift workers. A slight increase was also observed among the night workers.

These results were not significantly altered by further adjusting the data to account for other possible risk factors including family history of cancer, body mass index, smoking, alcohol consumption, job type, physical activity at work, perceived stress, educational level and marital status.

Kubo’s team suggests that reduced secretion of the hormone melatonin may be involved, since it helps induce sleep and has anticancer effects.

Because this is the first time that shift work has been identified as a risk factor for prostate cancer, they add that the “association needs to be replicated and confirmed in other settings.”

SOURCE: American Journal of Epidemiology, September 2006.