Social trust predicts sleep disorder at 6 years after the Great East Japan earthquake: data from a prospective cohort study

Background: The physical and psychological health impacts on victims of the Great East Japan Earthquake (GEJE) have lasted for a long time. Some cross-sectional studies have reported a relationship between social networks and/or social support and mental health among victims. Previous studies were cross-sectional observations at one time point after a disaster, it remains unclear whether the lack of social trust soon after the GEJE predicts long-term mental health outcomes among the victims. The objective of the present study was to examine prospectively the association between social trust soon after the GEJE and trends in sleep disorders up to 6 years after the GEJE. Methods: We conducted a health survey on residents living in two areas affected by the GEJE. We analyzed data from 1293 adults (aged >= 18 years) who had participated in an initial health survey. The participants responded to a self-administrated questionnaire composed of items on health condition, mental health, including sleep disorders (based on the Athens Insomnia Scale [AIS]), and social trust. We classified the participants into two categories (high or low) based on the level of social trust at the first health survey. A linear mixed model was used to estimate trends in AIS scores in relation to social trust at the first health survey. Results: The AIS scores of participants in the low social trust group were significantly higher than those in the high social trust group throughout the 6 years after the GEJE (P<0.01). After adjusting for some covariates, the AIS score estimate for the participants who had low social trust was 1.30 point higher than those for the participants who had high social trust. Conclusion: Social trust at 3 to 5 months after the GEJE predicted AIS scores at 6 years after the GEJE among victims. This finding suggests that it may be possible to identify people who have a lower potential for mental resilience from disaster damage over the long term. Further, health interventions for this high-risk group could help promote resilience after a disaster.