Recovery from a life-disrupting disaster presents challenges to everyone. But the elderly may struggle with difficulty in receiving appropriate medical care, isolation due to loss of social support networks, and trauma due to relocation after decades of having lived in the same place. Previous studies of natural disasters and seniors have not assessed how these challenges affect the elderly’s ability to function.

A recent paper published in PNAS showed that the degree to which housing was damaged due to the 2011 Great East Japan Earthquake and Tsunami was associated with a cognitive decline in survivors who were 65 years old or older. This study is the first to suggest that life-disrupting disaster events may hasten the onset of dementia in the elderly.

The 2011 Great East Japan Earthquake and Tsunami caused housing damage and loss that displaced an estimated 340,000 residents of Japan. This event presented a unique “natural experiment,” in which researchers had access to a discrete population that had been exposed to the natural disaster. Researchers studied 3,594 elderly survivors who had participated in the Japan Gerontological Evaluation Study from the city of Iwanuma, approximately 80 kilometers from the epicenter of the earthquake. The researchers examined their health status, health behaviors, social determinants of healthy aging, and the dementia symptoms.

This data was combined with the participants' demographic characteristics and earthquake/tsunami-related losses and was compared to their declines in cognitive ability. The extent of an individual's home’s destruction was significantly associated with dementia symptoms, particularly for those whose homes incurred major damage or were destroyed.

(To assess the level of home destruction, the researchers used data from field officers who surveyed the relevant properties. This procedure helped to ensure that the home damage variable was classified consistently and was not dependent on self-reporting, which can be biased.)

Though the extent of home damage was associated with dementia symptoms, the loss of relatives or friends wasn’t. This finding is unexpected because social engagement protects against cognitive decline. The loss of a social support network due to natural disaster would be expected to accelerate the occurrence of cognitive decline, but that is not what appeared to happen in this population.

The authors have speculated that this may be because they do not have information on the frequency of interaction among the participants and their lost friends and family. If they only interacted rarely, it could explain this finding. Future studies of this phenomenon should include frequency of interaction as an important variable when examining the impact of lost social contacts.

The researchers also examined the role that other factors may have played in this association, such as onset of depression and resulting lack of interaction with neighbors. Mediators are variables that are thought to be on the pathway between the cause (the earthquake) and effect (dementia). So, in this example, the loss of a home may have caused participants to become depressed or interact less with neighbors, which in turn may have accelerated their cognitive decline. When these mediators were included in the model, the effect of home damage on cognitive decline was attenuated and less striking.

Though previous studies hinted that there may be a connection between natural disasters and cognitive decline, this is the first to look into whether there might be a causal relationship. It uses a unique population to look into how disasters may expose the elderly to unique health risks. Future studies that probe these causal pathways more fully could indicate which post-disaster interventions could help older survivors.

PNAS, 2016. DOI: 10.1073/pnas.1607793113 (About DOIs).