The magnitude-9.0 earthquake and resulting tsunami that struck Japan in March 2011 killed 20,000 people and . Now there is evidence that they may also have contributed to cognitive decline in certain people.
at Harvard University and his colleagues wanted to know whether directly experiencing the earthquake and tsunami, as well as the disruption both left in their wake, had an effect on cognitive decline among people aged 65 years or older at the time.
鈥淚dentifying particularly vulnerable subpopulations is important because it will contribute to allocating public health resources in future emergencies,鈥� says Shiba.
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The researchers turned to a national study of people in Japan aged 65 years or older called . They focused their efforts on data taken from Iwanuma in Miyagi Prefecture, which was severely hit by the tsunami.
About 3350 adults with an average age of 73.2 took part in the initial survey, which occurred seven months before the disaster, and they were surveyed again in a follow-up study 2.5 years later. In a second follow-up survey that took place 5.5 years after the earthquake, 2664 of the adults took part. In each survey, participants completed a questionnaire that helped caregivers assess their current cognitive state.
After analysing the data, the team concluded that individuals who lost their home during the disaster typically experienced an increase in their rate of cognitive decline. Surprisingly, the researchers also found that the loss of a loved one during the disaster wasn鈥檛 associated with an increase in the subsequent rate of cognitive decline. Shiba says it is unclear why this was the case.
They also considered each individual鈥檚 unique circumstances to determine how these personal factors may have contributed to any cognitive decline. 鈥淢achine learning took care of this complex modelling part,鈥� says Shiba. The results suggested that low-income individuals were particularly vulnerable to experiencing a subsequent increase in the rate of cognitive decline. These people were also more likely to be older, unmarried and less well-educated.
This may be because those with less money and fewer social contacts may, because of their circumstances, have had to stay in temporary accommodation for longer and experienced greater social isolation, says Shiba.
He says the findings point to the need to build community hubs for when future disasters strike. 鈥淭his will encourage social interactions amongst residents to prevent social isolation,鈥� he says.
at Imperial College London in the UK says it makes sense that those from low-income backgrounds are likely to face greater impacts from the trauma of a natural disaster.
鈥淭his is an important study which highlights how the greatest burden of disasters such as earthquakes will be on those most vulnerable 鈥� even in high-income countries like Japan,鈥� he says.
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