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.