Recovering from a life-threatening disaster presents challenges for everyone. But the elderly can have difficulty getting proper medical care, isolation due to loss of social support networks, and trauma from moving after decades of living in the same place. Previous studies of natural disasters and seniors have not assessed how these challenges affect older people’s ability to function.
A recent article published in PNAS showed that the extent of housing damage from the 2011 major earthquake and tsunami in eastern Japan was associated with a cognitive decline in survivors aged 65 or older. This study is the first to suggest that life-disrupting disasters may precipitate the onset of dementia in the elderly.
The Great East Japan Earthquake and Tsunami of 2011 caused damage and loss to homes displacing an estimated 340,000 residents of Japan. This event presented a unique “natural experiment,” where researchers had access to a separate population exposed to the natural disaster. Researchers studied 3,594 elderly survivors who participated in the Japan Gerontological Evaluation Study from the town of Iwanuma, about 50 miles (80 km) from the quake’s epicenter. The researchers examined their health status, health behaviour, social determinants of healthy aging and the symptoms of dementia.
These data were combined with participants’ demographics and earthquake/tsunami-related losses and compared to their decline in cognitive ability. The extent of the destruction of a person’s home was significantly associated with dementia symptoms, especially for those whose homes suffered major damage or destruction.
(To assess the level of home destruction, the researchers used data from field officials surveying the relevant properties. This procedure helped ensure that the home damage variable was classified consistently and did not rely on self-reporting, which may be biased.)
While the extent of damage to the home was linked to symptoms of dementia, the loss of relatives or friends was not. This finding is unexpected because social engagement protects against cognitive decline. The loss of a social support network due to a natural disaster would be expected to accelerate the onset of cognitive decline, but that’s not what seemed to happen in this population.
The authors have speculated that this may be because they have no information on the frequency of interaction between the participants and their lost friends and family. If they interacted only rarely, this 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 other factors may have played in this association, such as the onset of depression and the resulting lack of interaction with neighbors. Mediators are variables that are thought to be in the path between the cause (the earthquake) and the 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 salient.
While previous studies have suggested a possible link between natural disasters and cognitive decline, this is the first study to examine whether there might be a causal relationship. It uses a unique population to explore how disasters can expose the elderly to unique health risks. Future studies that better examine these causal pathways could indicate which post-disaster interventions might help older survivors.
PNAS2016. DOI: 10.1073/pnas.1607793113 (About DOIs).