Association between night-shift frequency and metabolic syndrome among healthcare workers: a moderated mediation analysis of occupational stress and sleep quality.

Background: Night-shift work is highly prevalent among healthcare workers and has been associated with various adverse health outcomes, including metabolic syndrome (MetS). However, the psychosocial factors potentially involved in this association remain unclear. This study aimed to examine the association between night-shift frequency and MetS among healthcare workers and to explore the potential statistical indirect association through occupational stress, as well as whether the association between night-shift frequency and occupational stress varied according to sleep quality, providing scientific evidence for workplace health promotion and MetS prevention in healthcare settings. Methods: A hospital-based cross-sectional study involving 719 healthcare workers from a tertiary Grade A hospital in Shanxi Province, China, was conducted from January to March 2026. Participants were selected using stratified cluster sampling. Night-shift frequency, occupational stress, sleep quality, and relevant covariates were assessed using questionnaires, with occupational stress measured using the Effort-Reward Imbalance Questionnaire. MetS was determined based on physical examination and laboratory criteria. Multivariable logistic regression was used to evaluate the associations of night-shift frequency and occupational stress with MetS. Exploratory mediation analysis was performed to assess the statistical indirect association through occupational stress, and moderated mediation analysis was used to examine whether the association between night-shift frequency and occupational stress varied according to sleep quality. Results: Of the 719 healthcare workers, 124 (17.2%) had MetS. Compared with participants reporting 0 night shifts per month, those reporting 1-3 night shifts per month did not have significantly higher odds of MetS, whereas those reporting ≥4 night shifts per month had substantially higher adjusted odds (OR = 6.65, 95% CI 2.56-17.28). Exploratory mediation analysis showed a statistically significant indirect association through occupational stress in the ≥4 night shifts per month group (indirect effect 0.725, 95% CI 0.424-1.173), accounting for approximately 27.7% of the total association. The association between night-shift frequency and occupational stress was stronger at poorer sleep quality levels. In the ≥4-night-shift group, the conditional indirect effect increased from 0.350 (95% CI 0.149-0.647) at better sleep quality to 1.187 (95% CI 0.699-1.921) at poorer sleep quality. Conclusion: Higher night-shift frequency was associated with higher odds of MetS among healthcare workers. Exploratory analyses suggested a potential statistical indirect association through occupational stress, and this indirect association varied according to sleep quality. These findings may help inform future workplace health strategies focusing on night-shift scheduling, occupational stress management, metabolic health monitoring, and sleep health support.