Night shift work affects levels and timing of melatonin production

A study published in Cancer Epidemiology, Biomarkers and Prevention has been focused on circadian variation of melatonin, light exposure and diurnal preference in day and night shift workers of both sexes. This research, leaded by Manolis Kogevinas, researcher at CREAL, an ISGlobal research center, concludes that night shift work affects levels and timing of melatonin production and that may relate to future cancer risk for these workers.

Light-at-night has been shown in experimental studies to disrupt melatonin production but this has only partly been confirmed in studies of night shift workers. In this cross-sectional study we examined the circadian variation of melatonin in relation to shift status, individual levels of light-at-night exposure and diurnal preference, an attribute reflecting personal preference for activity in the morning or evening.

117 workers (75 night and 42 day) of both sexes, aged 22-64 years, were recruited from four companies. Participants collected urine samples from all voids over 24 hours and wore a data logger continuously recording their light exposure. Socio-demographic, occupational, lifestyle and diurnal preference information were collected by interview. Urinary 6-sulfatoxymelatonin, the main melatonin metabolite, concentrations were measured.

The results of the study were that mean 6-sulfatoxymelatonin levels were lower in night (10.9 ng/mg creatinine/h) compared to day workers (15.4). The lowest 6-sulfatoxymelatonin levels were observed in night workers with morning preference. “Peak time of 6-sulfatoxymelatonin production occurred 3 hours later in night compared to day workers. Phase delay was stronger among subjects with higher light-at-night exposure and number of nights worked”, explains Kyriaki Papantoniou, first author of the paper.

The main conclusion is that night shift workers had lower levels and a delay in peak time of 6-sulfatoxymelatonin production over a 24 hour period that may be related to future cancer risk.