8288908 Altered coordination between sleep timing and cortisol profiles in night-working female hospital employees

<h3>Objective</h3> Night-shift work is known to disrupt circadian rhythms, potentially leading to adverse health effects. This study investigated the relationship between sleep timing and cortisol secretion profiles among female hospital employees. <h3>Material and Methods</h3> 89 female hospital workers (68 shift workers, 21 non-shift workers) were included in this cross-sectional study. Shift workers worked rotating shifts, including night shifts, whereas non-shift workers maintained regular day shifts. Shift workers provided salivary cortisol samples collected at multiple time points during two consecutive day shifts and three consecutive night shifts. Non-shift workers collected their samples across two consecutive day shifts. Sleep timing was assessed through polysomnography and sleep diaries. Using generalized additive mixed models, we estimated shift-specific cortisol curves, considering the non-linear relationship between time since waking up and logarithmized cortisol levels, adjusted for age, chronotype, menopausal status, contraceptive use, stress load, smoking status. Each cortisol curve was summarized by cortisol awakening response (CAR), peak-to-bed slope, and total cortisol output. <h3>Results</h3> Shift workers on night shifts showed a flattened U-shaped cortisol profile after the post-awakening peak, with peak-to-bed slope close to zero (-0.02, 95%-CI = -0.82, 0.78). In the same women, a normal diurnal cortisol profile with a steep negative peak-to-bed slope after the post-awakening peak (-2.57, 95%-CI = -3.17, -1.98) was observed on day shifts. Day-shift cortisol curves were similar in shape for both, shift workers and non-shift workers, showing differences in mean cortisol levels at waking up (-0.41 log(nmol/L), 95%-CI = -0.79, -0.02) and in CAR (0.37 log(nmol/L), 95%-CI = 0.10, 0.63). <h3>Conclusion</h3> This study in female shift workers showed night-work associated circadian misalignment between timing of sleep and cortisol rhythm. These findings highlight the importance of considering circadian biology in occupational health, particularly for professions requiring night work.