Relationships among shift work, hair cortisol concentration and sleep disorders: a cross-sectional study in China

Objective The present study was designed to demonstrate the relationships among shift work, hair cortisol concentration (HCC) and sleep disorders. Design A cross-sectional study. Setting Three petroleum administrations in Karamay city of Xinjiang, China. Participants 435 individuals including 164 males and 271 females participated in the research. Outcome measures Information on shift work was collected by a self-administered questionnaire. HCC was determined using an automatic radioimmunoassay instrument. Sleep quality was measured on the Pittsburgh Sleep Quality Index scale. Results Shiftwork was associated with an increased prevalence of sleep disorders compared with the fixed day shift (two shifts: OR 3.11, 95% CI 1.57 to 6.19; three shifts: OR 2.87, 95% CI 1.38 to 5.98; four shifts: OR 2.22, 95% CI 1.17 to 4.18; others: OR 3.88, 95% CI= 1.36 to 11.08). Workers with different shift patterns had higher HCC levels than day workers ((fixed day shift: geometric mean +/- geometric SD=2.33 +/- 1.65; two shifts: 3.76 +/- 1.47; three shifts: 3.15 +/- 1.64; four shifts: 3.81 +/- 1.55; others: 3.60 +/- 1.33) ng/g hair, eta(2)=0.174) and high HCC was associated with the higher prevalence of sleep disorders (OR 4.46, 95% CI 2.70 to 7.35). The mediating effect of HCC on the relationship between shift work and sleep disorders was 0.25 (95% CI 0.09 to 0.41). Conclusion We found that, when compared with the fixed day shift, shiftwork was associated with both the higher HCC, and also with an increased risk of sleep disorders. High HCC was associated with the occurrence of sleep disorders. In addition, HCC had mediating effect in shift work and sleep disorders. Thus, HCC can be considered as an early marker of shiftwork circadian disruption to early detection and management of sleep disorders.