Chronotype, Night Shift Work, and Diurnal Salivary Cortisol Rhythms Among Healthcare Professionals

Background: Chronotype is a determinant of tolerance to shift work; however, its physiological and psychological correlates remain insufficiently explored in healthcare workers. This study investigated associations between chronotype, perceived stress, sleep quality, and health behaviours in a large cohort of shift-working nurses and physicians. Additionally, diurnal salivary cortisol patterns were characterised in a physiological subsample. Methods: A cross-sectional study was conducted with 451 participants (77% female; mean age 42 ± 11 years) completing validated instruments, including the Perceived Stress Scale (PSS), Athens Insomnia Scale (AIS), Patient Health Questionnaire Somatic Symptom Scale (PHQ-15), and reduced Morningness-Eveningness Questionnaire (rMEQ). In addition, a prospective pilot substudy was performed in a physiological subsample of nurses (n = 40), in which salivary cortisol was measured at three time points during both day and night shifts. Results: Evening chronotype exhibited a higher prevalence of insomnia (70%) and elevated AIS scores (8.2 ± 4.2, p < 0.001). In the physiological subsample, evening types demonstrated a significantly attenuated cortisol awakening response (6.5 ± 5.1 nmol/L, p = 0.02) and a flatter diurnal cortisol slope during day shifts (p = 0.01). Logistic regression indicated that increased age, somatic symptom burden, and perceived stress were significant risk factors for insomnia, whereas morningness was protective (OR = 0.89, p = 0.003). Conclusions: Evening chronotype among healthcare professionals is associated with altered hypothalamic-pituitary-adrenal axis regulation and impaired sleep quality. These findings highlight the potential utility of chronotype-based scheduling and behavioural interventions targeting circadian misalignment to improve occupational health outcomes in shift-working populations.