Grant: Travel Awards - Institute Community Support

Background: Shift work has emerged as a risk factor for many chronic diseases, particularly cardiovascular disease (CVD). While the biological pathway by which shift work increases a person's CVD risk is still not fully understood, it is hypothesized that disruption of cortisol during night work is an intermediate. The aim of this study is to determine whether total cortisol production, diurnal pattern, and cortisol variability mediates the relationship between current shift work status and cardiometabolic risk among female hospital employees. Methods/Results: 326 female employees (166 rotating shift workers, 160 day workers) from a hospital in Southeastern Ontario, Canada participated in this cross-sectional, biomarker study. Current shift work exposure and other variables were reported in personal interviews. Urinary free cortisol was measured at every void over two 24-hour cycles, which included one-night shift for shift workers. Diurnal cortisol production and cortisol pattern were calculated, as well as the magnitude of variation for both production and pattern. Cardiometabolic risk criteria was determined through clinical exams. A cardiometabolic risk score was created based on score created by Hillier & colleagues (2012). Current shift work is associated with metabolic syndrome and a higher cardiometabolic risk score. Shift work is also associated with lower levels of diurnal cortisol production and a greater magnitude of variation in pattern. We found that diurnal cortisol production partially mediates the relationship between shift work and the cardiometabolic risk score. There is no evidence that the cortisol pattern or the magnitudes of variation are intermediates. Conclusion: Shift work is associated with metabolic syndrome and a higher cardiometabolic risk score. Diurnal cortisol production partially mediates the relationship between current shift work and cardiometabolic risk, while cortisol pattern and variability do not appear to be mediators.