Increased and Mistimed Sex Hormone Production in Night Shift Workers

Background: Night shift work has been associated with an increased risk for breast and prostate cancer. The effect of circadian disruption on sex steroid production is a possible underlying mechanism, underinvestigated in humans. We have assessed daily rhythms of sex hormones and melatonin in night and day shift workers of both sexes. Methods: We recruited 75 night and 42 day workers, ages 22 to 64 years, in different working settings. Participants collected urine samples from all voids over 24 hours on a working day. Urinary concentrations of 16 sex steroid hormones and metabolites (estrogens, progestagens, and androgens) and 6-sulfatoxymelatonin were measured in all samples. Mean levels and peak time of total and individual metabolite production were compared between night and day workers. Results: Night workers had higher levels of total progestagens [geometric mean ratio (GMR) 1.65; 95% confidence intervals (CI), 1.17–2.32] and androgens (GMR: 1.44; 95% CI, 1.03–2.00), compared with day workers, after adjusting for potential confounders. The increased sex hormone levels among night shift workers were not related to the observed suppression of 6-sulfatoxymelatonin. Peak time of androgens was significantly later among night workers, compared with day workers (testosterone: 12:14 hours; 10:06-14:48 vs. 08:35 hours; 06:52-10:46). Conclusions: We found increased levels of progestagens and androgens as well as delayed peak androgen production in night shift workers compared with day workers. Impact: The increase and mistiming of sex hormone production may explain part of the increased risk for hormone-related cancers observed in night shift workers. Cancer Epidemiol Biomarkers Prev; 24(5); 854–63. ©2015 AACR .