The associations of shift work exposure and chronotype with sleep problems among Hong Kong nurses: results from the HKNight cohort baseline

Shift work is often associated with poor sleep outcomes; however, findings vary among different individual chronotypes. This study aimed to investigate the associations between various shift work exposures, individual chronotypes, and scale-assessed sleep quality and insomnia among Hong Kong nurses. The study was conducted between March 2022 and February 2023. The participants completed a self-reported online questionnaire. Sleep outcomes were assessed using the Pittsburgh Sleep Quality Index (PSQI score ≥ 6 indicates poor sleep quality) and the Insomnia Severity Index (ISI score ≥ 8 indicates insomnia). Chronotype was measured using the Munich Chronotype Questionnaire. Multivariate ordinal logistic regression models were used to estimate the associations. We recruited 718 full-time nurses and 208 daytime office workers. Compared with daytime office workers, night shift nurses had significantly greater odds of having a PSQI score ≥ 6 (adjusted odds ratio [aOR] = 3.38, 95% CI: 2.37–4.81) and an ISI score ≥ 8 (aOR = 1.69, 95% CI: 1.18–2.43). Additionally, workers with an evening chronotype presented greater odds of having a PSQI score ≥ 6 compared with those with a morning type (aOR = 1.69, 95% CI: 1.17–2.44). Among shift nurses, the odds of a PSQI score ≥ 6 increased with the number of night shifts worked in the previous month (Ptrend = 0.028). Furthermore, the start time of afternoon shifts demonstrated a quadratic relationship with nurses whose PSQI score was ≥ 6 (Ptrend <0.001). Poor mental health significantly mediated the effect of night shift work on poor sleep. Night shift work and evening chronotype were significantly associated with poor sleep quality and insomnia among Hong Kong nurses, and this association was partially mediated by poor mental health. Optimizing shift schedules (particularly afternoon timing) and enhancing mental health support may mitigate these effects. Chronotype-aligned scheduling may not improve sleep quality among nurses.