RELATIONSHIP BETWEEN SLEEP QUALITY AND SERUM CORTISOL LEVELS AMONG HEALTHCARE WORKERS: A CROSS-SECTIONAL STUDY

Abstract

Background: Work undertaken during night-shift hours is commonly linked with sleep disturbance, circadian rhythm disruption and increased physiological stress among healthcare providers. Objective: The objective of this study was to explore the relationship between sleep quality and serum cortisol among healthcare workers working regular night shifts in Baghdad, Iraq. Methods: Two hundred healthcare workers working in governmental hospitals in Baghdad completed a cross-sectional study between October 2025 and February 2026. The sleep quality was measured by the Pittsburgh Sleep Quality Index (PSQI). Serum cortisol concentrations were measured using the VIDAS® Cortisol assay, an enzyme-linked fluorescent assay (ELFA) technology. Results: Poor sleep quality was common, with 71.0% of participants poor sleepers. Serum cortisol concentrations increased significantly among poor sleepers compared with good sleepers in the sample (24.7 ± 4.6 vs. 13.4 ± 2.8 μg/dL, p < 0.001). Increasing frequency of monthly night-shift duties resulted in progressively rising levels of cortisol. There was a significant positive Pearson correlation established between PSQI score and serum cortisol concentrations (r = 0.72, p < 0.001), whereas sleep duration showed a significant negative correlation (r = −0.66, p < 0.001). Multiple linear regression found that: PSQI score, sleep duration, and night-shift frequency were significant independent variables predicting serum cortisol levels (Adjusted R² = 0.61, p < 0.001). Conclusions: Poor sleep quality and frequent night-shift duty were significantly associated with high serum cortisol levels in the healthcare workers indicating a close association between occupational sleep disturbance and physiological stress response.