Elderly people who were uprooted from damaged or destroyed homes and who lost touch with their neighbors after the 2011 tsunami in Japan were more likely to experience increased symptoms of dementia than those who were able to stay in their homes, according to a new study from Harvard T.H. Chan School of Public Health. The study was the first to look at dementia as a potential health risk in the aftermath of a disaster.
The study was published online October 24 in an early edition of the Proceedings of the National Academy of Sciences journal (PNAS).
“In the aftermath of disasters, most people focus on mental health issues like PTSD,” said Dr. Hiroyuki Hikichi, research fellow at Harvard and lead author of the study. “But our study suggests that cognitive decline is also an important issue. It appears that relocation to a temporary shelter after a disaster may have the unintended effect of separating people not just from their homes but from their neighbors—and both may speed up cognitive decline among vulnerable people.”
The Harvard researchers, working with colleagues in Japan, were able to conduct a “natural experiment” among a group of elderly residents of the coastal city of Iwanuma, located about 80 kilometers west of the earthquake epicenter, where nearly half the land area was inundated by the tsunami. Seven months before the disaster, elderly residents of Iwanuma had been surveyed about their health as part of an ongoing study of aging called the Japan Gerontological Evaluation Study (JAGES). Two-and-a-half years after the tsunami, the researchers conducted a follow-up survey among the same group.
Out of 3,566 survivors of the tsunami disaster aged 65 or older—some who were able to remain in their homes and some who were forced out—38.0 percent said they lost relatives and/or friends and 58.9 percent reported property damage. In the pre-tsunami survey, 4.1 percent of respondents had been assessed with dementia symptoms; after the tsunami, the percentage jumped to 11.5 percent. The prevalence of stroke increased, from 2.8 percent to 6.5 percent, as did the prevalence of hypertension (54.0 percent to 57.2 percent). The percentage of people who reported not interacting with their neighbors—not even with greetings—nearly doubled, from 1.5 percent to 2.9 percent.
Those who wound up in temporary housing after their houses were either destroyed or sustained major damage had the highest levels of cognitive decline. There was a strong dose-response association: People whose houses were more severely damaged experienced more cognitive decline. Depression and declines in informal social interactions with friends and neighbors appeared to play a role in the link.
By contrast, loss of relatives and/or friends did not seem to impact cognitive abilities.
Funding for the study came from the National Institutes of Health (R01 AG042463); Grants-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (KAKENHI 23243070, KAKENHI 22390400, and KAKENHI 24390469); a Health Labour Sciences Research Grant from the Japanese Ministry of Health, Labour and Welfare (H24-Choju-Wakate-009); and a grant from the Strategic Research Foundation Grant-Aided Project for Private Universities from the Japanese Ministry of Education, Culture, Sports, Science and Technology (S0991035).
“Increased risk of dementia in the aftermath of the 2011 Great East Japan Earthquake and Tsunami,” Hiroyuki Hikichi, Jun Aida, Katsunori Kondo, Toru Tsuboya, Yusuke Matsuyama, S.V. Subramanian, and Ichiro Kawachi, PNAS, online October 24, 2016, doi: 10.1073/pnas.1607793113