The present study aims to compare 6-sulfatoxymelatonin (aMT6s) secretion patterns and levels of cortisol and sex hormones (estradiol, progesterone, DHEA, DHEAS, and testosterone) among rotating night-shift workers and day-shift workers. We performed a cross-sectional study in Cantabria (northern Spain) including 136 women (73 day-shift workers and 63 rotating night-shift workers). Blood and urine samples were obtained after two consecutive working days. Differences in means were estimated using ANCOVA, stratified by menopausal status, ovulation phase, and adjusted for season, age, body mass index, consumption of cigarettes in the last 24 h. aMT6s circadian rhythm was analyzed using the cosinor analysis. The present study showed that rotating night-shift workers had lower excretion of aMT6s than day-shift workers (mesor = 50.26 ng aMT6s/mg creatinine in women with rotating night shift versus 88.79 ng aMT6s/mg creatinine in women with day shift), lower fluctuation (amplitude = 45.24 ng aMT6s/mg creatinine in rotating night-shift workers versus 79.71 ng aMT6s/mg creatinine in day-shift workers), and a later acrophase (aMT6s peak time: 08:31 in rotating night-shift workers versus 07:13 h in day-shift workers). Additionally, women with rotating night shift had higher estradiol and progesterone levels, compared to day workers, especially in the follicular phase on the menstrual cycle.
Keywords: Breast cancer risk; circadian disruption; day-shift work; light exposure; rotating night shift work.