Objective: Low sleep quality (LSQ) activates the hypothalamic–pituitary–adrenal (HPA) axis and is related to arousal. Nursing staff, who work in shifts, tend to exhibit LSQ, which affects the level of vigor after awakening. This study investigated the effects of nocturnal sleep quality on diurnal cortisol profiles and sustained attention in day-shift nurses. Method: This study adopted a prospective cross-sectional design. Participants were recruited from a university-affiliated hospital in northern Taiwan. In the initial stage of this study, the Chinese Pittsburgh Sleep Quality Index (PSQI) Questionnaire was administered to 199 participants to categorize them as either LSQ (PSQI > 5) or high sleep quality (HSQ; PSQI ≤ 5). Participants were then randomly sampled from the two groups. Nocturnal sleep data and four diurnal saliva samples were collected for each participant. Sustained attention was measured before they started work. A total of 32 and 29 participants in the HSQ and LSQ groups, respectively, completed the data collection process. Results: Compared with the HSQ group, the LSQ group exhibited earlier wake-up times (p =.02), a flatter cortisol awakening response (CAR) slope (p <.01), a flatter morning-to-evening slope (p <.01), and prolonged reaction speed and mean reaction time before starting work (p <.01). Conclusion: Compared with the HSQ group, the LSQ group exhibited impaired HPA-axis regulation, with a flatter CAR and diurnal cortisol slope and poor sustained attention in the morning. Nursing staff are advised to achieve HSQ to improve attention and performance levels and maintain optimum work safety.
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