DOES DISRUPTION IN CORTISOL PRODUCTION MEDIATE THE RELATIONSHIP BETWEEN SHIFT WORK AND CARDIOMETABOLIC RISK? – A CROSS-SECTIONAL STUDY AMONG FEMALE HOSPITAL EMPLOYEES

Abstract

Shift work has emerged as a risk factor for many chronic diseases, particularly cardiovascular disease (CVD). While the exact 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. Thus, the aim of this study is to determine whether total cortisol production, diurnal pattern, and cortisol variability mediate the relationship between current shift work (SW) status and cardiometabolic risk among female hospital employees. 326 female employees (166 rotating shift workers and 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. Metabolic syndrome (MetS) criteria was determined through clinical exams. Diurnal cortisol production (AUCG) and cortisol pattern (AUCI) were calculated, as well as the magnitude of variation for both AUCG and AUCI. A cardiometabolic risk score (MetS score) was created based on score created by Hillier and colleagues (2012). Current shift work is associated with MetS (OR=2.41, 95% CI: 1.25, 4.64) and a higher MetS 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 mediates the relationship between shift work and the MetS score. There is no evidence that the cortisol pattern or the magnitudes of variation are intermediates between shift work and the MetS score. Magnitude of AUCG variation is also associated with the MetS score while controlling for shift work, suggesting that changes in cortisol production, independent of shift work, are associated with an increased risk of MetS. Shift work is associated with the metabolic syndrome and with higher cardiometabolic risk. Current diurnal cortisol production mediates the relationship between current shift work and metabolic syndrome, while cortisol pattern and cortisol variability did not appear to be mediators. Future studies will investigate path analyses that consider other intermediates, such as sleep and work stress, in the pathway between shift work and CVD.