Elderly people forced out of their homes and separated from neighbors in the aftermath of a natural disaster may be more prone to dementia than survivors who are able to remain in their dwellings, a new study suggests.

This, at least, is how things unfolded after the 2011 tsunami and earthquake in the Tohoku region, according to the study of 3,556 elderly survivors.

“In the aftermath of disasters, most people focus on mental health issues like post-traumatic stress disorder,” said lead study author Hiroyuki Hikichi, a public health researcher at Harvard University in Boston. “But our study suggests that cognitive decline is also an important issue.”

While previous research has documented cognitive decline and dementia among the elderly after disasters, including hurricanes Katrina and Rita in the U.S., the current study of survivors from the 2011 earthquake and tsunami in Japan offers a unique snapshot of the factors that may influence the odds that these problems will emerge, Hikichi said by email.

That’s because in the current study, researchers had access to survey data documenting risk factors and rates of dementia both before and after the disaster.

Researchers examined survey data from a group of elderly residents of the coastal city of Iwanuma, Miyagi Prefecture. The earthquake’s center was in the ocean about 80 km (50 miles) due east of Iwanuma, where nearly half the land area was inundated by the subsequent 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). Then, 2½ years after the tsunami, the researchers conducted a follow-up survey among surviving members of the same group.

Overall, 38 percent of the participants said they lost relatives and friends and about 59 percent reported property damage after the disaster, researchers reported in Proceedings of the National Academy of Sciences on Oct. 24.

Before the tsunami, about 4 percent of these older adults had at least some symptoms of dementia, the study found. About 30 months later, roughly 12 percent of them had some symptoms of dementia.

Strokes became more common, too. About 3 percent reported a previous stroke before the disaster, compared to almost 7 percent afterward.

At the same time, the proportion of people who reported no contact with neighbors — not even greetings on the street — almost doubled from 1.5 percent to 2.9 percent.

People who wound up in temporary housing after their houses were either destroyed or sustained major damage had the highest levels of cognitive decline. The decline was also steeper for people with the most damaged homes, compared to people with homes that had only mild damage.

Depression and declines in informal social interactions with friends and neighbors appeared to influence the odds of dementia or cognitive decline after the disaster, but the loss of family and friends didn’t seem to be a factor.

“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,” Hikichi said.

The study does not, however, prove that housing damage causes dementia. One limitation of the analysis is that researchers can’t rule out the possibility that people at risk for dementia and cognitive decline were also more likely to be living in homes with greater potential for damage, the authors noted.

Still, the link between stress and dementia is well known and it’s quite plausible that housing damage and displacement after a disaster would be a significant source of stress, said Dr. Richard Lipton, an aging and neurology researcher at Albert Einstein College of Medicine and Montefiore Medical Center in New York.

Stress from displacement could lead to surges in cortisol, a stress hormone, and activation of what’s known as the sympathetic nervous system, a fight or flight response, potentially increasing memory decline and the risk of dementia, Lipton, who wasn’t involved in the study, said by email.

“Under this hypothesis we would predict that stress management, meditation, social support and other interventions might reduce the impact of catastrophic events on brain function,” Lipton added.

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