Chapter 1 Introduction

1.1 Population Aging

1.1.1 Aging in the 21st Century

Population aging—the process by which the median age and the relative proportion of older people are increasing—is widespread across the world. In 1950，there were 205 million people age≥60 years throughout the world（Figure 1.1）. Fifty years later，the world’s population of people age≥60 years tripled，and is estimated to reach nearly 2 billion by 2050. Between 2000 and 2050，the proportion of the world’s population≥60 years old will double from about 11% to 22%；the proportion will increase from 20% to 32% in more developed regions and from 8% to 20% in less developed regions[1]（Figure 1.1）.

A society is considered to be an “aging society” when elderly individuals—those age≥65 years—comprise more than 7% of the population；in an “aged society”，elderly individuals comprise more than 14% of the total population；and in a “super-aged society”，this age group accounts for more than 21% of the total population. Table 1.1 shows that for selected countries，the dates when the population reached，or is expected to reach，each point. Typically，the transition from 7% to 14% of elderly individuals took longer in countries that reached 7% at an earlier date. For example，Sweden and France reached 7% before 1900，and took 85 years and 115 years to reach 14%，respectively. That same transition required only 24 years in Japan，which was an exceptionally short period compared to that for other countries. More developed countries are in general in a more advanced stage of demographic transition，as a consequence of several factors，such as advanced industrial economics and public health systems；thus，the proportions of older individuals in such countries are projected to remain significantly higher than those in less developed regions；indeed，growth of the older population is often more remarkable in more developed counties（Figure 1.1）. However，the older population is also growing at a faster rate in less developed regions. As a result，the world will be faced with populations that are aging at a rapid speed.

Figure 1.1 Numbers and proportions of population age≥60 years：1950-2050

Source：United Nations Department of Economic and Social Affairs，2011[2].

Table 1.1 Aging rate in selected countries

Population aging occurs due to two distinct demographic changes：falling fertility rates and increasing longevity. The overall median age for the world rose from 23.9 years in 1950 to 26.7 years in 2000，and is forecasted to reach 37.9 years by 2050. The corresponding figures for more developed regions as a whole are 29.0 years in 1950，37.4 years in 2000，and 44.3 years in 2050；in contrast，the figures for less developed regions overall are 21.5 years in 1950，24.1 years in 2000，and 36.8 years in 2050[3]. People are living longer：continuing gains in life expectancy at birth have been experienced globally by both males and females（Figure 1.2）. Over the last 6 decades（1950-2010），global life expectancy at birth increased by almost 20 years. However，large variations exist，e.g.，between people living in different regions and between genders. The gain in life expectancy at birth for males was 11.2 years in more developed regions and 23.7 years in less developed regions；in females，such gains were 12.9 years in more developed regions and 26.7 years in less developed regions. Sustained gender differences in life expectancy at birth from 1950-2010 have also been observed，ranging from 5.0-6.7 years in more developed regions and 0.8-3.8 years in less developed regions. In addition，as can be seen from data from select countries in the Organization for Economic Co-operation and Development（OECD）presented in Figure 1.3，the life expectancy at age 65 years has been rising for both men and women，although to a somewhat larger degree in women，since 1960. On average，life expectancy at age 65 years increased by 4.4 years for males and by 5.6 years for females in OECD countries from 1960-2009. However，some countries recorded much greater increases. For example，the average life expectancy at age 65 years in Japan rose by 7.3 years for males and 9.9 years for females. This means that people are spending more years as elderly individuals. Moreover，many of the very old lose their ability to live independently due to limited mobility，frailty，or mental health problems. Thus，along with other health challenges for the 21st century，it is important to prepare health providers and societies to meet the specific needs of older populations with respect to both quality of life（QOL）and long-term care（LTC）prevention.

1.1.2 Population Aging in Japan

In 2018，the total Japanese population was 126.44 million；about 35.58 million were age≥65 years（15.46 million men and 20.12 million women）. The elderly（age≥65 years）represented 28.1% of the total population，in which individuals age 65-74 years（young-old）and≥75 years（old-old）represented 13.9% and 14.2%，respectively，of the population. Thus，more than 1 in every 4 people in Japan was≥65 years old，and more than 1 in 10 was≥75 years old. Women are overrepresented due to their longer average life expectancy；for example，there were 16 women for every 10 men among people≥75 years old. The proportion of people age≥75 years was 2.1% in 1970 when Japan became an aging society，a figure that had almost doubled by 1990 to 4.8%，and nearly quintupled by 2010 to 10.9%；it is expected to increase to 24.5% by 2050（Figure 1.4）.

Figure 1.2 Male and female life expectancy at birth：1950-2050

Source：United Nations Department of Economic and Social Affairs，2011[4].

Figure 1.3 Male and female life expectancy at age 65 years in selected OECD countries：1960 and 2009

Source：OECD Health Data 2011；World Bank and national sources for non-OECD countries[5].

Figure 1.4 Population aging trends in Japan：1950-2060

Source：Up to 2010，Ministry of Internal Affairs and Communications，“Population Census.” After 2015，National Institute of Population and Social Research，“Projected Population of Japan” in 2011，based on the estimated figure on the assumption that birth and death rates are ranked medium[6].

With limited international migration，the rapid aging of the Japanese population is attributed to the steady prolongation of its life expectancy and the sharp drop in its birthrate. Japan has one of the highest life expectancies in the world，and this figure continues to increase（Figure 1.5）. The average life expectancy at birth was 81.09 for males and 87.26 for females in 2017，and these figures are expected to increase to 84.02 years for males and 90.40 for females by 2050，after which female life expectancy is projected to exceed 90 years. Furthermore，the average life expectancy at age 65 years was 18.9 years for males and 24.0 years for females in 2009. Compared to 11.6 years for males and 14.1 years for females in 1960，the life expectancy at age 65 years has substantially increased，particularly for women（Figure 1.3）. As the total population size decreases，aging will continue to accelerate. By 2055，the Japanese population is projected to drop to 90 million，with 36 million（41%）people age≥65 years.

Figure 1.5 Trends in average life expectancy at birth：1955-2055

Source：Up to 2005，Ministry of Internal Affairs and Communications，“Complete life tables.” “Abridged life table” in 2009. After 2015，National Institute of Population and Social Research，“Projected Population of Japan” in 2005，based on the estimated figure on the assumption that birth and death rates are ranked medium[7].

Geographic variation of the aging rate in Japan exists. Among the 47 prefectures in 2011，Akita had the highest rate of 29.7% while Okinawa had the lowest rate of 17.3%. Prefectures in major urban areas have relatively low aging rates，while 35 prefectures show rates higher than the national average of 28.1%. The aging rate in all 47 prefectures is expected to increase in the future. In 2035，the highest percentage of elderly individuals will reach 41.0% in Akita Prefecture；the lowest figure will reach 27.7% in Okinawa Prefecture. Simultaneously，increases in aging rates will differ between prefectures；for example，the aging rate will increase remarkably from 2011 to 2035 in Saitama Prefecture（12.9%）and Chiba（12.2%）. Thus，services for the rapidly increasing elderly populations in some regions will be necessary.

1.1.3 Theories about the Population Health Status Changes Due to Aging

In 1984，a general model of health transitions was proposed that distinguished between mortality，morbidity，and disability to explain the different states of life：total survival，survival without chronic disease，and disability-free survival. The model is portrayed using three main curves：“mortality，” “disability，” and “morbidity”[8]. Three main theoretical hypotheses that highlight the effects that an observed decline in mortality might have on the morbidity and disability of the elderly in the future are described below.

Compression of Morbidity

Fries initially proposed that life expectancy was approaching a maximum limit in the 1980s[9]. This optimistic compression scenario suggests that the burden of illness may be reduced by postponing the onset of chronic diseases/disability，due to medical progress and improved general health improvements，such as prevention of being overweight or obese，quitting smoking，and physical practices. Thus，the proportion and a quantum lifetime spent in good health toward the end of life has increased. The health transition model can illustrate the hypothesis that if the “mortality” curve remains stable，both the “disability” and “morbidity” curves shift upward and the areas between “mortality” with “disability” and “morbidity” are reduced. However，in combination with the increased number of older people in this scenario in the future，long-term care costs would be mitigated if extra years of life are spent in good health. Thus，the policy implication of this rather optimistic theory is that health resources should be shifted to the later stages of life and for a shorter period of time[10].

Expansion of Morbidity

The expansion of morbidity theory poses the pessimistic view that gains in life expectancy predominantly occur through the technological advances that have been made in extending the life of those with disease and disability[11]. In detail，medical advances extended the lifespan of a much broader spectrum of the population，thus increasing the survival of the frail elderly and leading to more years lived with non-fatal disabling diseases of old age，such as Parkinson’s disease，dementia，and arthritis[12][13]. Gruenberg[14] originally characterized this rather expressively as the “failure of success”. The health transition model can illustrate the hypothesis that if both the “disability” and “morbidity” curves remain stable，the “mortality” curve shifts to the right and the areas between “mortality” with “disability” and “morbidity” are expanded. Thus，as the older population grows，the demand for health and social care services as well as the pressure on careers and communities will rise dramatically due to the increase in morbidity.

Dynamic Equilibrium

Manton[15] proposed a dynamic equilibrium in which progress is made in prolonging both total and healthy lifespans，leading to approximate stability in the ratio of healthy lifespan to total lifespan. In other words，although more disability is possible，it would be light and moderate，with a dynamic equilibrium maintained. The health transition model illustrates this hypothesis by expanding the area between “morbidity” and “mortality”；if the disability is considered to be severe morbidity，the area between “disability” and “mortality” remains the same. This scenario does not envisage greater long-term social care costs，but primary care and long-term health services could experience greater pressure[16].

1.1.4 Global Studies on the Population Health Status Changes Due to Aging

The above-mentioned hypotheses constitute the background for several studies，which attempted to understand whether the mortality reduction is accompanied by improvement or deterioration of the population’s health status[17]. However，these studies did not yield consistent results.

Since 1991，many published studies have contributed considerably to the body of evidence indicating an absolute expansion of morbidity/disability，such as in Australia[18]，the United Kingdom（UK）[19]，Japan[20]，and Taiwan[21]. The first wave of very robust evidence for this altered view of disability trends in the older population came from the United States[22][23]. In the National Long Term Care Study（NLTCS）conducted in the late 1980s and the 1990s，the age-specific disability rates were lower in the 1990s than in the 1980s，indicating a significant reduction in the rate of functional decline in old age during those two decades. In addition，a few other countries，such as Austria[24] and Denmark[25]，appeared to have experienced an actual contraction of the period of disability at the end of life. Strong evidence from New Zealand[26] and the Netherlands[27][28] indicated an expansion of disability attributed primarily to an increase in age-specific prevalence rates for mild-to-moderate disability rather than severe disability，thereby lending support to the dynamic equilibrium hypothesis. A recent OECD study yielded mixed results regarding activities of daily living（ADL）disability trends，which denote a severe level of disability among individuals age≥65 years. Of the 12 countries studied，only 5（Denmark，Finland，Italy，the Netherlands，and the United States）showed clear evidence of a decline in disability among elderly people. Three countries（Belgium，Japan，and Sweden）reported an increased rate of severe disability among people age≥65 years，and two countries（Australia and Canada）reported stable rates. In France and the UK，data from different surveys showed different trends in ADL disability rates，making it impossible to reach any definitive conclusions regarding the direction of the trend[29][30].

Most countries are experiencing a strong increase in life expectancy due to medical，cultural，and social causes. It is unknown whether an upper limit of human life expectancy exists and what this limit could be. The resulting patterns in different countries can be concluded as follows：1）living longer exposes more people to non-fatal disabling diseases of old age；2）improved control of the progression of chronic diseases leads to a dynamic equilibrium between the decrease of mortality and the increase in disability；3）improved medical care and health behaviors compressed the number of time people live with disease and disability into a short period before death；and 4）the eventual emergence of very old and frail populations leads to a new expansion of morbidity[31]. Even though these four theories are generally understood as mutually exclusive alternatives，the causal factors they each highlight are not. The theories are mutually exclusive insofar as they state that the primary causal driver behind the continuing postponement of death by chronic disease is either delayed onset（as a result of improved primary prevention），delayed progression of disease（as a result of improved secondary prevention），or increased survival with severe disease（as a result of improved tertiary prevention）[32].