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.
Shift work is associated with an increased risk of cardiovascular diseases (CVD). Disruption of cortisol production is a potential underlying mechanism. This study explored the associations of diurnal quantity and pattern of cortisol production in relation to (1) current shift work status (exclusive day versus rotating days and nights), (2) years of past shift work and (3) parameters of rotating shift work (timing, length and intensity). Female hospital employees (160 day workers and 168 rotating shift workers) from southeastern Ontario, Canada, participated in a cross-sectional study. Participants completed a baseline questionnaire and measures of body height, weight, and waist circumference were taken. Midstream urine samples were collected over two separate 24-hour periods to measure creatinine-adjusted cortisol. Total diurnal cortisol production and pattern were described with two measures of the area under the curve. The effect of shift work on cortisol was modeled using multivariable linear regression analyses. Cortisol production in day workers and shift workers on their day shift were similar; however, shift workers on the night shift had flatter diurnal cortisol curves and produced less cortisol. This suggests that night work is associated with an acute attenuation of cortisol production.
Introduction Cardiovascular disease (CVD) is currently the leading cause of death worldwide, contributing to 30% of all deaths. CVD etiology is complex, with many modifiable and nonmodifiable risk factors. Epidemiological evidence generally supports an association between shiftwork and an increased risk for CVD. However, the underlying physiological mechanisms remain poorly understood. Limited research suggests that the production of cortisol may differ between shift workers and non-shift workers, resulting in physiological changes that potentially increase the risk of CVD among shift workers. This study will focus on females who comprise the largest proportion of workers in healthcare settings. Objectives 1) To describe and compare total cortisol levels and its diurnal pattern in relation to current shiftwork status, and cumulative duration of exposure to shiftwork. 2) To determine if current shiftwork status and/or cumulative duration are associated with total cortisol levels, and diurnal pattern.
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