While it is well-known that a severe natural disaster can increase the risk for certain mental disorders, such as post-traumatic stress disorder (PTSD), a new study finds that this type of trauma can also increase the risk of dementia in the elderly.
Researchers at the Harvard T.H. Chan School of Public Health found that elderly people who had been uprooted from their destroyed homes and had lost touch with their neighbors after the 2011 tsunami in Japan were much more likely to experience increased symptoms of dementia than those who were able to stay in their homes.
The study, published in the Proceedings of the National Academy of Sciences journal (PNAS), is the first to look at dementia as a potential health risk in the aftermath of a disaster.
“In the aftermath of disasters, most people focus on mental health issues like PTSD,” said Dr. Hiroyuki Hikichi, research fellow at Harvard Chan School 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 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, the participants had completed a health survey 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, 38 percent said they lost relatives and/or friends and 58.9 percent reported property damage.
In the pre-tsunami survey, 4.1 percent of the participants had been assessed with dementia symptoms; after the tsunami, this number nearly tripled to 11.5 percent. The prevalence of stroke more than doubled from 2.8 percent to 6.5 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.
The prevalence of hypertension increased slightly from 54 percent to 57.2 percent.
Elderly residents who ended up moving to temporary housing after their homes were either significantly damaged or destroyed had the highest levels of cognitive decline. There was a strong dose-response association: People whose homes were more severely damaged experienced more cognitive decline. Depression and social withdrawal from 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.