Night Shifts Implicated in Increased Prostate Cancer Risk

Shift work is positively associated with higher levels of prostate-specific antigen (PSA) levels in men between the ages of 40 and 65, according to results of a recent study published in the Journal of the National Cancer Institute.

Nearly a quarter of all American workers participate in some form of rotating shift work. This can lead to disrupted circadian rhythms, thought to be caused by loss of melatonin production. A correlation between shift work and cancer of different forms, including prostate cancer, has been suggested by previous studies. To this end, this study from the Division of Sleep Medicine at Brigham and Women’s Hospital attempted to evaluate the levels of PSA in male workers to see if elevated PSA is correlated with shift work.

Data on men were gathered from three consecutive National Health and Nutrition Examination Survey (NHANES) studies. A total of 2,017 men aged 40 years or older and younger than 65 with known PSA test results from 2005 to 2010 were included. Men with prior cancer history were excluded, except in the case of non–melanoma skin cancer. Shift work was defined as employment with regular night or rotating shifts. A threshold of 4 ng/mL was chosen as a binary cutoff point for further study, primarily because this value has been the typical threshold for clinical screening. Total PSA levels > 4 ng/mL have been previously shown to increase the risk of prostate cancer risk and mortality. The percentage of free PSA was also assessed, since depressed levels (ie, below 25%) of free PSA have been correlated with more aggressive disease.

Of the 2,017 men, 233 engaged in shift work. The average age between the non–shift workers and shift workers was comparable (50.4 vs 51.4, respectively), as were average body characteristics such as height and weight. Shift workers obtained significantly less sleep per night when compared with non–shift workers (6.2 vs 6.7 hours, P < .001).

PSA levels for shift workers was found to be elevated 2.48 times as often as non–shift workers. When adjusted for factors such as age, sleep duration, and health insurance status, this odds ratio reached 2.62. When factoring in the free PSA levels in the blood, shift workers were found to be high risk compared with non–shift workers with an odds ratio of 3.13.

Overall, this study was the first work that demonstrated an elevation in PSA levels in workers with routine disruption of circadian rhythm, in agreement with previous reports indicating increased cancer risk in shift workers. It remains to be seen whether length of time at a job that requires regular night shifts will enhance PSA levels over time. Remarked the authors, “there were insufficient cases to stratify based on years of shift work with the current employer, and type of shift worked with former employers was not assessed in this survey.” Future studies may be able to extend the results presented by prospective study design to determine the association between circadian disruption and PSA levels more directly.