The risk of insomnia by work schedule instability in Korean firefighters.

Background: Firefighters are exposed to shift work, as well as unpredictable emergency calls and traumatic events, which can lead to sleep problems. This study aimed to investigate the risk of insomnia by work schedule instability in Korean firefighters.
Methods: This study used the Insomnia Severity Index to assess the insomnia in firefighters. The work schedule stability was classified with the frequency of the substitute work and the timing of notification for work schedule changes. Logistic regression analysis was used to assess the adjusted odds ratio of insomnia by work schedule stability with covariates including sex, age, education, smoking, alcohol, caffeine intake, shift type, job, and underlying conditions.
Results: Of the 8,587 individuals, 751 (8.75%) had moderate to severe insomnia (Insomnia Severity Index ≥ 15). The prevalence of insomnia was statistically significantly higher as the frequency of substitute work increased: <1 time per month (6.8%), 1-2 times (9.5%), 3-5 times (13.4%), and more than 5 times (15.7%) (p < 0.001). Additionally, the prevalence of insomnia was statistically significantly higher when the timing of the schedule change notification was urgent or irregular: no change or several weeks before (5.4%), several days before (7.9%), one day before or on the day (11.2%), irregularly notification (11.6%) (p < 0.001). In comparison to the group with good frequency of the substitute work/good timing of schedule change notification group, the adjusted odds ratios of insomnia were 1.480 (95% confidence interval [CI]: 1.237-1.771) for Good/Bad group, 1.862 (95% CI: 1.340-2.588) for Bad/Good group, and 1.885 (95% CI: 1.366-2.602) for Bad/Bad group.
Conclusions: Work schedule instability was important risk factor of insomnia in firefighters. It suggests that improving the stability of work schedules could be a key strategy for reducing sleep problems in this occupational group.