Psychological distress and the incident risk of functional disability in elderly survivors after the Great East Japan Earthquake

Background: We conducted a prospective cohort study to investigate whether psychological distress would have increased the incident risk of functional disability after the 2011 Great East Japan Earthquake. Methods: First phase data pertaining to psychological distress and other lifestyle factors were collected from 1037 subjects aged >= 65 years, from June to December 2011, in four affected areas of Miyagi prefecture in Japan. Psychological distress was measured by the Kessler 6-item psychological distress scale (K6), and classified into three categories (K6 score <= 9, 10-12, >= 13). Outcome data on functional disability were collected from the public Long-term Care Insurance database. Participants were followed up for about 2.6 years. The Cox model was used to calculate the multivariate hazard ratios (HRs) and 95% confidence intervals (CIs). Results: During the follow-up period, 118 participants were certified as incident disability (43.8 disability events per 1000 person-years). Compared with the lowest category (K6 score <= 9), participants in the highest category (K6 score >= 13) had a significantly higher risk of functional disability (HR = 2.65, 95% CI = 1.35-5.18, p = 0.002). In order to consider reverse causality, we conducted analysis excluding all incidents and deaths that occurred within the first year of follow-up, but our findings remained unchanged. Limitations: We did not consider all potential confounders and use of appropriate medication. Conclusions: The present study has demonstrated that psychological distress was associated with an increased risk of functional disability among elderly survivors of a natural disaster.