Author(s): MURATA, H., SAKURAI, A., TAKANO, D., SUZUKI, R., HORINO, M., MATSUSHIMA, S., HIRASAWA, A., MATSUDA, T., SHIBATA, S., Institution: KYORIN UNIVERSITY, Country: JAPAN, Abstract-ID: 714

Introduction: The night shift is an essential work pattern in a variety of fields, including the medical sector. However, shift work disrupts the body's natural circadian rhythm, which is associated with an increased risk of health problems such as cardiovascular disease and mental health disorders. The impact on psychological health can be severe; studies have suggested that night shift workers have higher rates of mood disorders, such as anxiety and depression. The cortisol awakening response (CAR), which reflects the reactivity of the hypothalamic–pituitary–adrenal (HPA) axis responsible for the body's stress response, has been reported to be associated with these risks to psychological health. However, the relationship between CAR and mood states has not yet been adequately investigated. The present study aimed to clarify differences in CAR between night-shift workers and non-night-shift workers, and to examine whether the association between CAR and mood state, as measured by the Profile of Mood States 2 (POMS2), varies according to work schedule.
Methods: A cross-sectional study was conducted on 40 healthy adults (20 in the night shift work [NSW] group and 20 in the day work [DW] group). Salivary cortisol levels were measured at six time points: upon waking; 30 minutes after waking; 60 minutes after waking; before lunch; at around 5 pm in the evening; and before bedtime. Mood states were evaluated using the Profile of Mood States-2 (POMS2), which assesses overall mood disturbance (Total Mood Disturbance: TMD) as well as each of the following subscales: Anger–Hostility (AH), Confusion–Bewilderment (CB), Depression–Dejection (DD), Fatigue–Inertia (FI), Tension–Anxiety (TA) and Vigor–Activity (VA). Furthermore, mental health was also assessed using the Quick Inventory of Depressive Symptomatology-Self-Report Japa (QIDS-J).
Results: In the between-group comparison, DWgroup had lower CAR-AUCg values and lower cortisol levels upon waking than NSW group (p<0.05). The QIDS-J score was significantly higher in NSW group than in DW group (p<0.05), indicating stronger depressive symptoms among night shift workers. No significant difference was observed in POMS2 score. Correlation analysis revealed that, within the night shift group, CAR-AUCg was negatively correlated with TMD (ρ = -0.49, p < 0.05) and with Anger-Hostility (AH) (ρ = -0.52, p < 0.05). Conversely, in the non-night shift group, CAR-AUCg positively correlated with TMD (ρ = 0.46, p < 0.05) and negatively correlated with vitality (VA) and friendliness (F) (VA: ρ = -0.53, p < 0.05; F: ρ = -0.52, p < 0.05).
Conclusion: Night shift workers exhibited reduced CAR levels reflecting HPA axis hyporesponsiveness, which was associated with mood states. This study suggests that some of the psychological health risks associated with night shift work may be explained by alterations in HPA axis responsiveness. This provides important insights into the health management of irregular workers.