6533b829fe1ef96bd128ab62

RESEARCH PRODUCT

Shift Work and Prostate Cancer Incidence in Industrial Workers

subject

description

In 2007 the International Agency for Research on Cancer (IARC) classified shift work involving circadian disruption as a probable human carcinogen (1). Most of the evidence for this is based on animal experiment models and only a few reliable epidemiological studies. The cancer best described to date is breast cancer; this has mainly been investigated in female nurses and flight attendants (2, 3). Shift work can also increase the incidence of prostate cancer, as plausibly described in a review article published in 2012 (4). Mechanistically, it is possible that nocturnal light exposure and disrupted circadian rhythms cause cancer, or that tumor growth is favored by hormonal mediation. Nocturnal light exposure suppresses melatonin secretion in the pineal gland. In vitro and in vivo experiments have shown that melatonin prevents or inhibits tumor growth, particularly that of prostate cancer, and that there is a dose–effect relationship (1, 5). The epidemiological evidence on prostate cancer comes from only a few studies involving individual data on shift work (6– 8) (Table 1). In studies of flight personnel, duration of employment or number of flight hours was used as a proxy measure (9– 11). In one large Scandinavian study, the probability of exposure was estimated using a job exposure matrix (12). Table 1 Review of earlier studies on shift work and on prostate cancer Earlier research of a cohort of 31 143 male production workers in the chemical industry, 45% of whom worked shifts, showed no overall increase in deaths from cancer or individual tumors (13, 14). This article investigates the incidence of prostate cancer in this cohort and examines earlier findings on overall tumor incidence in more detail (15). The complete scientific report is available online (16).