Counter‐clockwise shift‐work and prostate cancer: Putting pieces in the puzzle

Abstract

The retrospective cohort study 1 of prostate cancer risks among rotating shift-workers published by Dr Kubo et al. can be relevant for several reasons. In 2006, Kubo et al. were the first to investigate possibly elevated prostate cancer risks in male shift workers.2 At that time, their prospective cohort study evinced that rotating-shift workers were significantly at risk for prostate cancer. A little later, the 2007 International Agency for Research on Cancer (IARC) classification of "shift-work that involves circadian disruption is probably carcinogenic to humans" (Group 2A) 3 provided further impetus for observational studies into shift work and cancer.From scientific and public health viewpoints, this classification of a "probable" nexus of widespread and inevitable shift work, on the one hand , and epidemic and , thus far, mainly unpreventable cancers such as breast and prostate cancer, on the other, left us with a puzzle. What, if any, shift work conditions might increase the risk of what, if any, cancer? The IARC experts based their evaluation of epidemiological data almost exclusively on breast cancer in female nurses and flight personnel, 3 and an IARC press release called for studies of "potential risks in other professions and for other cancers". 4 In this vein, Dr Kubo et al. now contribute to filling in information regarding two important pieces of this puzzle.First, with regard to end-points, this study adds to the few studies that addressed prostate cancer. 2,5,6 Second , with regard to exposures, it appears that this study is unique insofar as it focused on counter-clockwise shift regimens. Although prior studies based on "shift work" status might have included such shift organization, we simply don't know when, and there could have been mixes of clockwise and counter-clockwise shifts. That the direction of shift rotation might be important information to consider has been pointed out by Foster and Kreitzman, who emphasized that it is not settled empirically whether forward or backward shift rotation is less favorable for shift workers. 7 It is indeed conceivable that, possibly depending on the shift workers' chronotypes, some individuals might do better with counter-clockwise rather than clockwise rotation of shifts. Importantly, therefore, we need factual data on the possible effects of counter-clockwise shifts. That the study by Kubo et al. used industry-based shift work data documented in an independent fashion (when compared with questionnaire or interview information) is a further asset. 8 Taken together, as the "remarkably high quality exposure information" on a "counterclockwise three-shift system" constitutes a key facet of this study, it would have been a candidate for inclusion in the abstract.A final reason as to why this study can be relevant is the fact that its results are now available in the public scientific domain. The authors point out that "some increase in the risk of prostate cancer for shift workers was observed , although the result was not statistically signific...

Length polymorphism in the Period 3 gene is associated with sleepiness and maladaptive circadian phase in night‐shift workers

“…It is well known that regular night work increases the risk for a variety of cardiovascular (Akerstedt and Knutsson, ; Czeisler et al ., ; Gamble et al ., ; Leclerc, ; Murata et al ., ; Puttonen et al ., ) and gastrointestinal (Vener et al ., ) disorders, as well as breast (Davis et al ., ; Kamdar et al ., ; Pijpe et al ., ; Wang et al ., ) and prostate (Conlon et al ., ; Erren et al ., ) cancers. Thus, in addition to the differences in circadian phase and sleepiness found in the present study, future investigations are needed to determine if night‐shift workers with different length polymorphisms in PER3 have differential long‐term health outcomes in response to working night‐shifts.…”

Response to Counter‐clockwise shift‐work and prostate cancer: Putting pieces in the puzzle (Author's Reply)

“…We thank Dr Thomas Erren and his colleagues 1 for their comments on our recent article on prostate cancer risk among shift workers. 2 In October 2007, an International Agency for Research on Cancer panel concluded that shift work involving circadian disruption is probably carcinogenic to humans.…”