Abstract
IMPORTANCE: Older adults are at high risk for cognitive impairments following natural disasters, but the persistence of such effects is not well understood. OBJECTIVE: To track older adults' postdisaster cognitive disability trajectories over a decade and examine associations of cognitive disability with disaster damage exposure. DESIGN, SETTING, AND PARTICIPANTS: This prospective cohort study used predisaster baseline surveys conducted in August 2010 and 4 follow-ups approximately every 3 years until November 10, 2022. Invitations were mailed at baseline to all citizens 65 years or older in Iwanuma City, Japan, a coastal municipality significantly impacted by the 2011 Great East Japan Earthquake and Tsunami. A total of 1988 respondents who were cognitively independent (ie, without cognitive disability) before the disaster completed the 4 postdisaster cognitive assessments. EXPOSURES: Experiences of residential damage, worsening financial conditions, loss of loved ones, and disruption in health care services. A composite score quantified these experiences, with higher scores indicating greater overall damage. MAIN OUTCOMES AND MEASURES: Cognitive disability level was assessed using a standardized in-home evaluation under a national long-term care insurance scheme. Trained investigators evaluated participants' activities of daily living, cognitive function, and presence of mental and/or behavioral disorders. Latent class growth analyses (LCGA) identified distinct cognitive disability trajectories. Primary outcomes consisted of inclusion in these trajectories. RESULTS: The analytic sample consisted of 1988 participants who were cognitively independent at baseline, with a mean (SD) age of 72.4 (5.4) years, of whom 1159 (58.3%) were female. LCGA identified 3 cognitive disability trajectories: high and gradual deterioration (277 [13.9%]; high levels of cognitive disability with increasing impairment over time), low and progressive deterioration (541 [27.2%]; low levels of cognitive disability with accelerated decline in cognitive function over time), and low and stable (1170 [58.9%]; low levels of cognitive disability that remained stable). In multinomial regression analyses with the low and stable trajectory serving as the reference, housing damage (adjusted odds ratio [AOR], 2.52; 95% CI, 1.26-5.04), worsening financial conditions (AOR, 1.83; 95% CI, 1.15-2.90), and disruption in health care services (AOR, 1.76; 95% CI, 1.03-2.99) were associated with high and gradual deterioration. Worsening financial conditions (AOR, 1.38; 95% CI, 1.01-1.90) and higher composite damage scores (AOR, 1.16; 95% CI, 1.01-1.34) were associated with low and progressive deterioration. These associations no longer remained after adjusting for postdisaster depressive symptoms. CONCLUSIONS AND RELEVANCE: In this cohort study of older adults who survived the 2011 Great East Japan Earthquake and Tsunami, disaster-related exposures were associated with worse long-term cognitive disability trajectories. These findings could inform tailored interventions to preserve cognitive function in older disaster survivors.