Shift Work, Chronotype, and Melatonin Patterns among Female Hospital Employees on Day and Night Shifts

Abstract

Background: Shift work-related carcinogenesis is hypothesized to be mediated by melatonin; however, few studies have considered the potential effect modification of this underlying pathway by chronotype or specific aspects of shift work such as the number of consecutive nights in a rotation. In this study, we examined melatonin patterns in relation to shift status, stratified by chronotype and number of consecutive night shifts, and cumulative lifetime exposure to shift work.Methods: Melatonin patterns of 261 female personnel (147 fixed-day and 114 on rotations, including nights) at Kingston General Hospital were analyzed using cosinor analysis. Urine samples were collected from all voids over a 48-hour specimen collection period for measurement of 6-sulfatoxymelatonin concentrations using the Buhlmann ELISA Kit. Chronotypes were assessed using mid-sleep time (MSF) derived from the Munich Chronotype Questionnaire (MCTQ). Sociodemographic, health, and occupational information were collected by questionnaire.Results: Rotational shift nurses working nights had a lower mesor and an earlier time of peak melatonin production compared to day-only workers. More pronounced differences in mesor and acrophase were seen among later chronotypes, and shift workers working !3 consecutive nights. Among nurses, cumulative shift work was associated with a reduction in mesor.Conclusion: These results suggest that evening-types and/or shift workers working !3 consecutive nights are more susceptible to adverse light-at-night effects, whereas long-term shift work may also chronically reduce melatonin levels.Impact: Cumulative and current exposure to shift work, including nights, affects level and timing of melatonin production, which may be related to carcinogenesis and cancer risk. Cancer Epidemiol Biomarkers Prev; 25(5); 830-8. Ó2016 AACR.

Sleep disruption, chronotype, shift work, and prostate cancer risk and mortality: a 30-year prospective cohort study of Finnish twins

“…Recent evidence suggests that chronotype may modify the degree of sleep and melatonin disruption that accompanies various shift patterns [18, 22, 23]. It is biologically plausible that chronotype may modify the association between shift work and cancer along several of these proposed pathways.…”

“…Such findings highlight the importance of looking beyond the cancer risk associated with working or sleeping in a particular time window to a more personalized examination of the risk associated with working in a time window that is not compatible with one’s diurnal preference. Investigators have therefore recently begun to incorporate measures of chronotype into studies of breast [19–21] and prostate [12] cancer, as well as studies of shift work and melatonin levels [22, 23]. …”

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