Association between unpredictable work schedule changes and sleep disorders among wage workers: Evidence from national working conditions surveys in Korea and Europe

OBJECTIVES: Unpredictable work schedule changes have emerged as a distinct occupational health concern, yet their association with chronic sleep disorders remains understudied. Given the contrasting institutional contexts of Korea and Europe, we hypothesized that the association would differ in magnitude between the two regions and examined this using a dose-response framework based on advance notice timing. METHODS: This cross-sectional study analyzed data from the 2017 Korean Working Conditions Survey and the 2015 European Working Conditions Survey. Habitual work schedule unpredictability, reflecting structural instability in working time arrangements, was assessed by advance notice timing. Sleep disorders were assessed using the validated Minimal Insomnia Symptom Scale. Stratified and sensitivity analyses were performed. RESULTS: Unpredictable schedule changes were associated with higher odds of sleep disorders in Korea (adjusted OR = 2.544, 95% CI: 2.195-2.948) and Europe (adjusted OR = 1.787, 95% CI: 1.543-2.070), with a formally confirmed regional difference (p for interaction < 0.0001). Risk increased progressively as advance notice shortened, demonstrating a clear dose-response relationship. Among subgroups, a statistically significant interaction was identified for long working hours in Korea, with stronger associations observed among those without overtime. CONCLUSION: Habitual work schedule unpredictability is a distinct occupational risk factor for sleep disorders. The observed dose-response pattern suggests that greater advance notice may be associated with lower risk, highlighting schedule predictability as a potential occupational health priority warranting regulatory and organizational attention.