Japanese population projected to live longer without dementia A new microsimulation projects that over the next 20 years, Japanese people will live longer without dementia, but older women with a less than high school education will benefit less than men. Research news

April 27, 2022

A blue bar chart and a red bar chart, showing projected cases of dementia for men and women in 2043 based on educational background.

These bar charts show projected life expectancy for men and women aged 65 years in 2016 and 2043, with and without dementia, and by educational background. ©2022 The Lancet Public Health, Kasajima, et al. CC BY 4.0

A new detailed microsimulation, using a database of 40 million people, has examined the future of Japan’s aging population up to 2043. It projects that more people will live longer, and that overall years spent living with dementia will decrease. However, the model highlighted the diversity of impacts on different segments of the population, as Japanese women with a less than high school education aged 75 and over may be disproportionately affected by both dementia and frailty. Better understanding where health gaps like this exist can help inform public health planning, to minimize future economic costs and support those most in need.

Taking care of the older members of society is a common concern around the world. Japan is famous for its long-lived residents, the number of which continues to rise. In 2020, almost 30% of the Japanese population was aged 65 years or older, and this age group is not projected to peak until 2034. Caring for people with age-related ailments, such as dementia and frailty, poses a challenge both to individuals and public health care systems.

Microsimulation models, which are computer models that can provide detailed analysis on an individual basis, are currently used to project future population health in some countries, such as the U.K. and the U.S. Professor Hideki Hashimoto and researchers at the University of Tokyo, along with researchers from Stanford University in the U.S., wanted to create a new microsimulation model for Japan, which would take into account more diverse conditions than had been considered before.

“We developed a new Japanese microsimulation model that accounts for 13 chronic conditions (including heart disease, stroke, diabetes, depression and dependency), as well as frailty and dementia,” explained Hashimoto.“Using an ultralarge data system, we were able to ‘follow’ a virtual cohort of more than 40 million people aged 60 and over from 2016 to 2043.”

According to Hashimoto, projections of aging in Japan usually rely on the “average” status of older people and so don’t consider the diversity of the population. “I believe that problems of aging are a matter of health gaps over the course of people’s lives,” he said. “Our projection brings attention to a widening health gap among older people. It highlighted that women with a less than high school education aged 75 or over are more likely to be affected.”

Identifying where health gaps like this exist could be used to better inform public policy, not only about health care but other influential aspects of life. “Japan’s case may suggest that improvement in educational attainment, as well as population health, could be a key to making a healthier and more manageable aging society,” said Hashimoto.

Positively, this study shows hope for a future where many people live longer and more healthy lives. “People might believe that an increase in cases of dementia is inescapable, given population aging. However, in this study we found that in Japan, despite an aging population, the number of people with dementia is expected to decrease over the next two decades,” said Hashimoto. “Population aging does not necessarily mean an increase of social burden for care, but it does bring a diversity of problems that requires careful study and science-based policy attention, to close the health gap.”


Megumi Kasajima, Karen Eggleston, Shoki Kusaka, Hiroki Matsui, Tomoki Tanaka, Bo-Kyung Son, Katsuya Iijima, Kazuo Goda, Masaru Kitsuregawa, Jay Bhattacharya, Hideki Hashimoto , "Projecting prevalence of frailty and dementia and the economic cost of care in Japan from 2016 to 2043: a microsimulation modelling study," Lancet Public Health 2022; 7: e458–68: April 27, 2022, doi:10.1016/S2468-2667(22)00044-5.
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