Lecture No.10
Population Aging

Hajime INOUE began his professional journey as a pediatric resident in Tokyo before dedicating himself to fieldwork as part of the Maternal and Child Health program in rural Philippines. Following post-graduate studies in public health, Dr. Inoue joined the Japanese Ministry of Health, Labour, and Welfare, where he amassed a wealth of technical expertise across various critical areas of global health, including UHC, Community Health, Health Emergency Response, Health Promotion, Population Ageing, Pharmaceutical Regulation, and Anti-Microbial Resistance (AMR). He has served as a Senior Advisor to the Director-General of the WHO and as Special Representative for AMR, bringing his extensive political acumen to bear as the G20 and G7 Sherpa of WHO. Among his recent achievements are the development of a new financing mechanism, the Contingency Fund for Emergency at WHO, the management of Japan's largest national hospital as its Director-General, and his pivotal role in crafting the national response plan for COVID-19 as the chief technical officer of the cabinet secretariat. Dr. Inoue's recent appointments include serving as an advisor at the World Bank’s Health, Nutrition, and Population program, and currently serving as Assistant Minister for Global Health at the Japanese Ministry of Health, Labor and Welfare. He holds a Medical Degree from Tottori University (Japan), a Master of International Health from the University of Tokyo (Japan), a Master of Public Health from Harvard School of Public Health (USA), and a Doctor of Public Health from Teikyo University (Japan).

A conceptual model was presented showing the evolution of survival curves from the 19th century through the 21st century. In the 19th century, roughly 20 percent of newborns did not reach age five, and by age 65, half had died. By the 20th century, the majority reached 65. Now, in the 21st century, more than half of the Japanese population reaches 80. Japan has approached what appears to be a near-ultimate status for survival curves, with only small margins remaining for future extension.

Epidemiological transition and the changing disease burden

The demographic transition has been accompanied by an epidemiological transition. Data comparing global disease burden in 1990 with Japan's disease burden in 2023 reveals marked differences. In 1990, communicable diseases—including neonatal conditions, lower respiratory infections, diarrhea, measles, and malaria—accounted for roughly half of the total disease burden. Child survival was the central focus of global health, premature death was common across the life course, and non-communicable diseases played a secondary role. Population aging was not yet a defining global phenomenon (Figure 2).

In contrast, Japan in 2023 presents a different picture. Communicable diseases now constitute only a small fraction of the disease burden, while non-communicable diseases account for approximately 80 percent of the total. Among these, Alzheimer's disease represents one of the largest and most rapidly growing burdens, alongside pancreatic cancer and prostate cancer. Other major conditions include stroke, ischemic heart disease, back pain, chronic obstructive pulmonary disease, chronic kidney disease, and diabetes (Figure 3). 

The contrast between 1990 globally and 2023 in Japan can be summarized across several dimensions: population structure has shifted from young to super-aging; the main health challenge has moved from survival to living with chronic conditions; dominant diseases have changed from communicable and nutritional conditions to non-communicable diseases; major causes of burden have shifted from diarrhea and pneumonia to cancer, dementia, and diabetes; the nature of disease burden has changed from premature death to long-term disability; and population aging has become a defining driver of health challenges.

Many diseases are age-related, and with population aging, their prevalence increases correspondingly. Data on Alzheimer's disease prevalence by age group illustrates this point. Among those aged 65 to 69, Alzheimer's prevalence is only one to two percent. However, prevalence increases with age, and among those 85 years and older, it reaches approximately 30 percent. Previously, reaching 85 was uncommon in Japan, so Alzheimer's was not a major issue. Now that nearly half the population reaches this age group, Alzheimer's has become a significant emerging challenge.

Similar patterns apply to hearing impairment. While not a serious issue for those in their forties and fifties, hearing loss becomes increasingly prevalent in the sixties, seventies, and eighties. By age 80—which is no longer rare in Japan—the majority of the population experiences some degree of hearing impairment. Age itself, though not a modifiable risk factor, functions as a significant risk for many conditions.

Japan's population structure and the baby boomer generations

Japan's current population pyramid has a distinctive shape with two bulges. The first represents the post-war baby boom generation (the “Dankai” generation), born between1947 to 1950, who are now in their late seventies. The second represents the “Dankai Junior” generation—the children of the baby boomers—who are currently around 50 years old. Notably, a third wave did not occur.

The implications of this structure become clear when considering what happens over the next decades. In five years, the baby boomer generation will be over 80. In ten years, they will approach 90, while the Dankai Junior generation will be entering their sixties—an age when conditions such as hearing impairment and dementia become more prevalent.

Projections for 2055 illustrate an unprecedented population pyramid—completely inverted from the traditional shape. In a conventional pyramid, infants constitute the most populous segment, with numbers declining through each successive age group. In Japan's projected 2055 pyramid, the most populous age segment will be those who are 82 years old. No society in human history has experienced such an extreme demographic structure.

An ultra-long-term perspective spanning the years from 1400 to 2400 can help to contextualize Japan's current situation (Figure 4). 

Before 1900, the proportion of the population aged 65 and over was small, reaching only five percent by the last century. Currently, the aging rate in Japan is approximately 30 percent—meaning three out of ten Japanese are 65 or older. This figure is projected to further increase in the next 30 years before gradually declining. The next three decades therefore represent a unique period in Japanese and human history.

The financial implications are substantial. Medical and long-term care expenditures increase with age. As the baby boomer generation moves into older age brackets over the next 10 to 20 years, the financial pressure on the health system will be considerable. There are concerns that Japan may not be able to sustain its health systems during this period.

However, the aging rate, the proportion of the population aged 65 and over, represents only one dimension of the challenge. Two additional dimensions require consideration: the socioeconomic characteristics of seniors, and the living environment where aging occurs.

Regarding the changing nature of seniors, a comparison between the baby boomer generation and the Dankai Junior generation reveals important differences. Many baby boomers have spouses, whereas 10 to 25 percent of the junior generation remain single. Baby boomers typically have two children, while the junior generation averages approximately one. Baby boomers often have multiple siblings, which is less common for the junior generation. Baby boomers benefited from stable lifetime employment, enabling decent savings and pensions; the junior generation frequently did not enjoy such stability, affecting their future financial security. Furthermore, Japan's national economic power was stronger when the baby boomers entered old age; it may be weaker when the junior generation ages. These factors suggest that when the Dankai Junior generation becomes elderly in 20 to 30 years, they may face more difficult circumstances.

The third dimension concerns the environment in which aging takes place. Within Japan, aging rates vary significantly by region, with the Greater Tokyo area experiencing some of the fastest population aging ever observed in human history. This pattern results from urbanization trends. After World War II, around 1950, only one-third of Japan's population lived in urban settings. This figure has now exceeded two-thirds. For decades, younger workers moved from rural prefectures to Tokyo for employment, settling in the suburban outskirts such as Chiba and Kanagawa.

This migration has created distinct challenges. In rural areas, the issue is a shortage of younger generations to care for the elderly who remain. In urban areas, the issue is caring for seniors in isolation. Young workers who moved to Tokyo suburbs in the 1960s and 1970s are now in their seventies; they did not return to their rural hometowns but remained in urban settings. This is why the Tokyo metropolitan area is among the fastest-aging regions in Japan and in the world (Figure 5)

A specific example is the large apartment complexes constructed in Tokyo's suburbs during the economic boom of the 1960s and 1970s. Young workers migrated from rural provinces to live in these complexes. Forty to fifty years later, these buildings remain, occupied by the same residents, now elderly. Their children have grown up and moved away, leaving only the aged parents. When asked what percentage of seniors in these housing complexes were born and raised there, the answer is zero percent. All migrated from elsewhere. They have limited social capital and often minimal connections with other residents—a stark contrast to traditional communities.

In traditional rural communities, social customs support aging in place. For example, elderly people living alone traditionally open their doors in the morning (weather permitting) to signal to neighbors that they are well. This informal monitoring system reflects strong community bonds developed over lifetimes. Such connections do not exist in the same way in urban apartment complexes, where residents may not even know who lives next door.

Global urbanization and mega cities

In terms of Japan’s experience within global urbanization trends, in 1960, there were only two mega cities (cities with populations exceeding 10 million): New York and Tokyo. By 1980, there were four, with Mexico City and São Paulo joining the list. By 2011, there were 23 mega cities, many in low- and middle-income countries in Africa, Latin America, India, and China. Currently in 2025, there are 37 mega cities worldwide.

Tokyo, which until recently was the world's largest city, has been surpassed—not by New York, Paris, or London, but by Jakarta and Dhaka. Many of the current top ten most populous urban areas are in emerging economies. These cities are undergoing the same process Tokyo experienced: young people migrate from rural areas to cities, and decades later, this workforce ages in place, often with limited social capital.

Japan is described as one generation ahead of middle-income countries and two generations ahead of low-income countries in experiencing this transition. What is occurring in the suburbs of Tokyo—aging populations with weak social connections in urban environments—represents the likely future for the suburbs of Cairo, Dhaka, Shanghai, and other mega cities in emerging countries. The situation currently being experienced in Greater Tokyo is therefore of interest to health policy planners worldwide.

Conclusion 

Dr. Inoue concluded by noting that population aging is fundamental to understanding any global health agenda. The 21st century is an era of longevity, not only in Japan but in many parts of the world, including low- and middle-income countries. For the first time in human history, the majority of the population can expect to live to their seventies, eighties, or even nineties. Japan is the first country to reach this status.

Through the mid-21st century, Japan will care for its baby boomers and their children, creating substantial financial pressures. The challenges ahead differ from those of previous eras of rural aging, when community bonds naturally provided support. In contemporary urban aging, social isolation is a defining issue alongside biological aging. This situation is not unique to Japan; the world is catching up. With 37 mega cities, many in emerging economies, the phenomenon of growing old in urban settings with limited social capital is becoming global.

The Greater Tokyo experience, including its suburban areas, represents one possible future for the world. Health policy planners from many countries are reportedly observing what is happening in Tokyo, recognizing that they will face similar challenges in the coming decades. Dr. Inoue emphasized that for effective policy brief writing on any health topic—whether cancer, health emergencies, cardiovascular disease, or obesity—an understanding of global population aging provides essential foundational knowledge.

Discussion

Dr. Kawahara noted that Dr. Inoue’s lecture had given students a robust framework for understanding the challenges we face in terms of aging and the transformation of disease burden. She also observed that because the disease burden has changed so dramatically, we now need to mobilize sectors beyond healthcare, including long-term care, employment, urban policy, education, and more. She asked where it is ideal to start, from a system perspective, in building cross-border and cross-sector partnerships between government and industry, and across ministries.

Dr. Inoue responded that traditionally the health ministry alone was responsible for the health of the population, but this will no longer be sufficient in coming decades. The primary reason is that health is now linked to financing challenges. As populations age, there is substantial pressure on healthcare financing. For this reason, greater involvement of finance ministries is essential. The Japanese government, in collaboration with WHO and the World Bank, established the UHC (Universal Health Coverage) Knowledge Hub last year to share knowledge on achieving universal health coverage. A distinctive feature of this hub is its effort to involve not only health ministries but also finance ministries—hence the collaboration with both WHO and the World Bank. One of the greatest challenges in maintaining health services or achieving UHC is financing, particularly as populations age.

A student asked what kind of academic skills or educational focus young people in Japan should pursue to support the aging society in the coming decades.

Dr. Inoue noted that many diseases affecting older populations are lifestyle-related, including cardiovascular diseases, stroke, diabetes, and even dementia. These conditions are closely linked to how people live. Therefore, rather than simply providing healthcare, one of the most important elements is modifying and improving the lifestyle of the population. This includes how people eat, exercise, sleep, and manage stress. Investment in health education and health literacy across all age groups is crucial. Effectively educating younger generations about maintaining healthy lifestyles in terms of exercise and diet can have substantial impact when they reach senior age. While more doctors, nurses, hospitals, and medicines will certainly be needed, one of the most effective interventions is modifying the lifestyle of individuals. This represents a key element for sustaining society in the coming decades.

A student observed that Japan could be called a pioneer in facing an aging society and asked what key lesson other countries should learn from Japan's experience.

Referring to the 2055 population pyramid slide, Dr. Inoue noted that Japan still has approximately 30 years before reaching this ultimate stage of population aging. There remains uncertainty about whether Japan can successfully manage this extreme demographic structure. Three potential lessons were identified by Dr. Inoue. First is the importance of managing the impact of urbanization. What Japan is experiencing is not simple population aging, but population aging combined with urbanization, social isolation, and limited social capital. The challenge of recreating community in urban settings is currently being addressed on the outskirts of Tokyo, and these experiments will provide lessons for the rest of the world. Second is how to manage the aging process financially. Effective approaches to financing a super-aged society have not yet been identified, and Japan's experience in this area will be instructive. Third is the importance of lifestyle. Approaches to improving the lifestyle of the population represent another area where Japan's successes and failures will offer lessons to other countries.

Dr. Kawahara, speaking on behalf of students who aspire to become globally minded professionals working across borders and sectors, asked what it truly takes to become a global health policy leader. He requested advice on the skills, mindset, and daily practices that would be most valuable.

Dr. Inoue observed that students in the class were already benefiting from learning from other countries. Many had come from their home countries to Japan, learning from the experiences of other nations and sharing experiences among classmates from different countries. This comparison of different health systems and situations cultivates more objective thinking in health policy planning. Students in the class already have significant benefits from attending the course by recognizing differences in policies and situations between their home countries and other parts of the world. This comparative perspective—viewing one's own country alongside others—makes policy planning more objective and more effective when applied in one’s home country. Dr. Inoue’s advice was to continue studying and comparing systems and situations across different countries.