Abstract
BACKGROUND: The present study aimed to investigate whether insomnia is associated with suicidal ideation (SI) among Japanese workers by conducting a multi-level analysis with sense of coherence (SOC) as a random effect. PARTICIPANTS AND PROCEDURE: A cross-sectional survey was conducted among 19,481 workers in Tsukuba, Japan. Data from 7,175 participants aged 20-65 years were included in the analysis. The Athens Insomnia Scale (AIS) was used as the independent variable, and SI over the past year was used as the dependent variable. SOC was measured using the five-point SOC-13 scale, and socioeconomic and health factors were investigated as covariates. Participants were divided into three groups (low, medium, and high) based on their SOC scores. Multilevel logistic regression analysis was performed to calculate odds ratios (OR) and 95% confidence intervals (95% CI). RESULTS: In the high-SOC group, only one person had SI. In a multi-level logistic analysis that excluded the high SOC group, insomnia was found to be associated with SI (OR = 2.26, 95% CI [1.75, 2.93]). Furthermore, the AIS sub-items "Final awakening earlier than desired" (OR = 1.26, 95% CI [1.05, 1.50]) and "Sense of well-being during the day" (OR = 1.63, 95% CI [1.34, 1.99]) were associated with SI. 8.95% or 11% of the variation in the presence or absence of SI was found to be explained by differences between SOC groups. CONCLUSIONS: The study highlights that insomnia is associated with SI, and that high SOC may reduce SI even under insomnia. Future longitudinal studies are needed to confirm whether high SOC reduces SI due to insomnia.