Shift Work and Cortisol Production Among Female Hospital Employees
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Background: Shift work is associated with an increased risk for cardiovascular diseases (CVD). This thesis focuses on the potential disruption of cortisol production by shift work, a proposed underlying pathway to CVD. Objectives: (1) To describe the diurnal quantity and pattern of cortisol production according to shift work status (exclusive-day, or rotating days and nights), and according to parameters of rotating shift work (timing, length, and intensity). (2) To determine how current shift work status and past shift work affects diurnal quantity and pattern of cortisol production. (3) To determine the effects of rotating shift work parameters on diurnal pattern and quantity of cortisol production. Methods: 328 female hospital employees (160 day workers, 168 rotating shift workers) participated in a cross-sectional study consisting of: (1) an initial interview and anthropometric assessment, (2) completion of a questionnaire package to ascertain work characteristics, and (3) collection of urine over a 48-hour period to measure creatinine-adjusted cortisol. Cortisol profiles and unadjusted summary measures were used to describe the quantity and pattern of diurnal cortisol production by shift work status and parameters of rotating shift work exposure. The effect of shift work on diurnal cortisol was determined using multivariable linear regression modeling. Results: Compared to day workers, rotating shift workers had flatter diurnal cortisol curves and produced less cortisol during their night shift cycle. However, during day shift cycles, there was no difference between shift workers and day workers in the quantity produced. Each additional year of shift work exposure was associated with an increase in diurnal cortisol production in day workers only. Conclusions: Night work is associated with acutely attenuated cortisol production, while a greater number of years of past shift work increased cortisol production. Thus, cortisol disruption may be a potential mechanism linking shift work to CVD development.