The average life expectancy in Japan has extended 4.2 years over the past 25 years as of 2015, while the gap between prefectures has widened during the same period, researchers have found.

A research team, led by Kenji Shibuya, a University of Tokyo professor of health policy, found that average life expectancy has increased to 83.2 years from 79.0 years during the quarter-century period.

They also discovered that the healthy life expectancy has also improved to 73.9 years as of 2015, from 70.4 years in 1990.

The research, which the authors claim is the first comprehensive study to look at a broader picture of disease burden and patterns in Japan, including by prefecture, found the increase in life expectancy was supported mostly by decreased mortality caused by cardiovascular diseases, particularly cerebrovascular diseases and heart diseases, neoplasms or cancers. Still they found the pace of that reduction has slowed since 2005.

It also showed the age-standardized death rates fell 29 percent over the 25 years during the time period thanks to a decline in the mortality attributed to heart disease and cancer. But the rate of deaths caused by Alzheimer’s disease and other types of dementia showed a significant increase in the 2005 to 2015 period.

The research also found that about 33.7 percent of deaths in 2015 were linked to behavioral risk factors such as smoking and high sodium consumption, followed by 24.5 percent that could be attributed to metabolic risks such as high blood pressure. Smoking was the leading risk factor for men in 2015, while unhealthy diet was the leading factor for women.

Despite an increase in life expectancy in all 47 prefectures, the regional gap has widened over the 25 years.

The gap between the longest life expectancy and the shortest life expectancy among prefectures was 2.5 years in 1990, with Nagano Prefecture (80.2) at the top while Aomori Prefecture (77.7) was at the bottom. In 2015, the gap was widened by 0.6 years to 3.1 years between Shiga Prefecture (84.7) and Aomori Prefecture (81.6).

The gap in healthy life expectancy among prefectures also widened to 2.7 years in 2015, from 2.3 years in 1990. Nagano and Shiga came first in the list for 1990 and 2015, respectively, while Kochi and Aomori, respectively, recorded the worst during the same period.

Despite widening disparities between prefectures, the research found factors such as smoking habits and unhealthy diets had no major relation to the gaps. Other factors such as medical costs and the number of doctors and nurses available also had little bearing on the disparity, the research showed.

Shibuya said the result suggests that pouring more money and human resources into prefectures with low life expectancy would not necessarily improve health outcomes, adding that he plans to conduct further research to learn the causes of the disparity.

“People tend to think we need to spend more money to fill in the gap. But our research this time suggests the amount of medical expenses or number of doctors have no correlations with the gap in prefectures’ average life expectancy,” Shibuya told the Japan Times Thursday.

“I think what we need to focus on is not how many resources we pour in, but rather how to use our resources more effectively to improve overall health care conditions,” he said.

The study was published Wednesday in the British medical journal The Lancet.

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