Associations Between the 2011 Great East Japan Earthquake and Tsunami and the Sleep and Mental Health of Japanese People: A 3-Wave Repeated Survey

Purpose: Large-scale natural disasters have an enormous physical and mental impact, immediately after they occur, on people living near the central disaster areas. It is known that, in the early stages, a seismic disaster triggers high rates of symptoms for insomnia, depression, and anxiety. However, little information is available about their medium- to longterm clinical outcomes. In this study, we conducted a repeated cross-sectional nationwide questionnaire survey to clarify changes in the prevalence of insomnia and its background factors after the Great East Japan Earthquake, a huge earthquake with a moment magnitude of 9.0 that occurred on March 11, 2011. Methods: We conducted a repeated cross-sectional survey in November 2009 (preearthquake, 1224 participants), July 2011 (4 months post-earthquake, 1259 participants), and August 2012 (18 months post-earthquake, 1289 participants) using stratified random sampling from 157 Japanese sites. Results: Compared to 2009, the prevalence of insomnia statistically increased nationwide immediately post-disaster (11.7% vs 21.2%; p < 0.001) but significantly decreased in 2012 compared to immediately after the earthquake (10.6% vs 21.2%; p < 0.001). In 2011, insomnia was most frequent in the central disaster area. Multivariable logistic regression models demonstrated the association between the following factors and increased risk of insomnia: being a woman (odds ratio [OR] 1.48, 95% confidence interval [CI]: 1.00-2.19), being employed in 2009 (OR 1.74, 95% CI: 1.15-2.62), and being of younger age group (20-64 years) in 2011 (OR 1.64, 95% CI: 1.12- 2.42) and 2012 (OR 2.50 95% CI: 1.47-4.23). Post-earthquake, the prevalence of insomnia symptoms in men increased, while the gender difference decreased and was no longer statistically significant. Additionally, insomnia was associated with psychological distress (scores >= 5 on the Kessler Psychological Distress Scale) in 2011 and 2012. Conclusion: This study demonstrated that the prevalence of insomnia was significantly higher after the earthquake. Moreover, individuals with insomnia were more likely to experience psychological distress after the earthquake that continued until 2012.