The Difference Between Lifespan and Health-span
- May 20
- 9 min read
Living longer has become common in Japan. Remaining healthy, independent, and mentally sharp into old age is a different challenge entirely.
TA Medical Research Team · Longevity Series · 6 min read · Health-span & Aging
The oldest woman in her village has never heard the word healthspan. She does not need to. At 97, she still tends her garden in the early morning before the heat arrives. Her knees are not what they were. But she moves. She eats with her neighbours three times a week. She has opinions about things. She laughs easily.
Her granddaughter, 44 years old, was diagnosed with hypertension last spring.
Scientists have been coming to Okinawa for decades to understand the difference between these two women. What they keep finding surprises them — not because it is complex, but because it is so ordinary.
01 Living Long and Living Well Are Not the Same Thing
Japan counts its years carefully. Average life expectancy, regularly among the highest in the world, is a source of quiet national pride. What gets counted far less carefully is what those years actually feel like from the inside.
In March 2026, researchers at the Buck Institute for Research on Aging published a detailed analysis of exactly this gap. Their starting point was something most people sense but rarely see measured: that the years medicine has added to human life are not always the years people imagined when they hoped to live long. Globally, the average person spends 8 to 10 years in poor health before they die — managing chronic conditions, losing physical independence, or in various degrees of cognitive decline. In Japan, those conditions have specific names and specific numbers, and they are worth knowing.
In Japan, the picture is specific. Dementia became the leading cause of death in 2021 and is expected to affect one in three people over 65 by 2030. Stroke touches one in six Japanese at some point in their lives. The lifetime risk of cancer is approaching one in two. Sarcopenia — the gradual loss of muscle mass and strength — affects more than half of all adults past 80 and is the primary reason independence is eventually lost. Diabetes, which rarely appears alone in death statistics, quietly accelerates all of the above and shortens life by six to eight years in those it affects.
None of these conditions appeared suddenly. Each built up over decades, in the background of ordinary life, before becoming visible. Which raises a question the Buck Institute researchers take seriously: if they were building for that long before anyone noticed, when was the right time to act?
02 What Changed on the Plate
There is one way to understand Japan’s current disease burden that does not require any medical knowledge at all. Look at what the country ate across three generations, and then look at how the country’s health began to change.
Period | What Was on the Plate | What Appeared in the Clinics |
1950 | Fish, tofu, miso soup, vegetables, sweet potato, rice. Frying pans uncommon. Sugar a festival luxury. Nothing processed. | Main killers: tuberculosis, parasites, respiratory infections. Diabetes, dementia, heart disease — barely counted. |
1975 | Frying became normal — tonkatsu, tempura, croquettes. Dairy into school lunches. Snacks and soft drinks on every shelf. Bread alongside rice. | Hypertension rising. Early heart disease. Cancer beginning its climb. |
1989–now | Cheap seed oils in every convenience store bento. Sugar in everything. Bread and instant noodles replacing rice for many. Meat dominant; fish, tofu, and miso increasingly occasional. | Dementia: Japan’s leading cause of death since 2021. Diabetes: 1 in 6 adults affected or at risk. Cancer lifetime risk: approaching 1 in 2. Sarcopenia: over half of adults past 80. |
In 1950, chronic lifestyle disease was rare enough in Japan to be barely counted. The food was plain — fish, tofu, miso, vegetables, rice — and almost nothing was processed. Sugar was expensive and seasonal. Frying pans were uncommon in most households.
The diseases now dominating Japan’s health statistics were not waiting in the genes. They were waiting in the food environment that came next. The shift was not dramatic in any single year — it accumulated across three generations, and its consequences are still accelerating. Japan is experiencing now the biological outcomes of choices made in the 1970s, 1980s, and 1990s.
Okinawa is where this trajectory is most visible, because it happened there first. The American military presence after the war brought fast food and convenience culture to the island before it reached the rest of Japan. The health statistics of the island’s younger generations tell a different story from those of their grandparents — not because the genetics changed, but because the food did.
The centenarians were not lucky. They were fed differently, for a long time, and their bodies reflect it.
03 What the Science Can Now Measure
The Buck Institute’s research asks why, at the cellular level, diet makes such a lasting difference to how people age. The answer they offer reframes aging itself.
Healthspan — the healthy portion of a life — is not a fixed allocation that depletes with time. It is shaped, continuously and significantly, by the conditions the body operates within over decades. Those conditions can be measured. And to a meaningful degree, they can be changed.
The evidence is large. Studies tracking more than 225,000 participants across the United States and Europe, some for nearly thirty years, show that people who maintain favourable lifestyle and metabolic conditions live 7 to 10 or more additional years free from major chronic disease. Not because of different genes — because their cells are working in a different environment. Each improvement to that environment, however incremental, adds to the healthy portion of life. The relationship holds across age groups and populations.
One molecule sits at the centre of this. NAD⁺ is present in every cell in the body. It powers the mitochondria that generate energy, activates the proteins that repair DNA damage, and manages the inflammatory responses that determine how well cells hold together under stress. By the fifties, NAD⁺ levels have typically fallen to about half of what they were at twenty. This is not a symptom of any particular disease. It is one of the upstream shifts that makes disease more likely — and it is directly connected to food. A diet high in processed food, sugar, and cheap seed oils chronically activates an enzyme that actively consumes NAD⁺. The 1989 column in the table above describes that diet, sustained across a population for decades.
The traditional Okinawan diet — low in sugar, almost nothing fried, built around fish and plants — happened to support NAD⁺ metabolism in ways that researchers are only now able to measure and explain. The elders were not supplementing anything. They were simply not depleting what their cells needed.
WHAT LARGE-SCALE RESEARCH SHOWS Studies across more than 225,000 participants show that lifestyle and metabolic conditions shift disease-free life expectancy by 7 to 10 years or more. The gains are dose-dependent — each improvement adds roughly one additional healthy year. They occur upstream of diagnosis, in the cellular environment, years before any condition becomes clinically visible. This is why the same conditions that produced the 1950 disease pattern and the 2025 disease pattern are the same conditions — just pointed in opposite directions. |
04 What Aging Actually Feels Like, Before It Has a Name
Aging rarely announces itself as a diagnosis. It arrives as something quieter and more gradual — changes in how a person feels and functions day to day, often years before any clinical threshold is crossed.
Researchers at the Buck Institute have developed a framework for measuring these changes — not through disease markers, but through eight functional dimensions of capacity that shift as people age. They call it the Spans Framework. Each dimension is grounded in measurable biology, but expressed in the language of daily experience.
Span | What It Actually Means |
Energy Span | How much energy you actually have through a day — not what you tell yourself you have, but what remains by late afternoon when nothing is left to borrow from. |
Strength Span | The physical capacity to carry shopping, climb stairs, get up from the floor. It declines so gradually that most people notice it only once it is already gone. |
Recovery Span | How quickly the body rights itself after a hard week, an illness, a bad run of sleep. In younger years this happens almost without thinking. Later it takes longer each time. |
Attention Span | The ability to hold a thought, follow a conversation, finish what you started. The fog that slowly settles in is not tiredness — it is a measurable change in brain function. |
Sleep Span | The depth of overnight repair, not just its duration. Light, fragmented sleep is not rest. The body uses deep sleep to do most of its maintenance work. |
Intelligence Span | The capacity to keep learning, reasoning, and adapting — not just recalling what was already known, but genuinely engaging with what is new. |
Confidence Span | Psychological resilience and the quality of connection with others. Social isolation accelerates biological aging in ways that are measurable in the blood, not just felt in the mind. |
Beauty Span | Skin quality, hair, posture, visible vitality. These are not vanity metrics. They are among the most visible external signals of what is happening inside. |
What makes this framework useful is that each of these dimensions begins changing earlier than most people expect — and each one is influenced by the same upstream conditions that shape NAD⁺ levels, inflammation, and metabolic function. Poor sleep affects energy and attention. Chronic low-grade inflammation, driven by a diet high in processed food, suppresses recovery and erodes strength over time. The connections run in every direction.
The prewar Okinawan elders, without knowing any of this biology, happened to sustain almost every dimension of this framework into very old age. They ate in ways that kept cellular energy production efficient. They moved through their days in ways that preserved muscle mass and coordination. Their social structures — the moai networks, the shared meals — sustained psychological resilience and cognitive engagement. Their sense of purpose, ikigai, continued past any conventional retirement age. They were not optimising. They were living in conditions that happened to support all eight Spans simultaneously, for decades.
05 Where It Actually Starts
The most important finding in the Buck Institute’s research is also the most counterintuitive: the conditions that determine how the later decades of life feel are largely set in the decades before. Not after a diagnosis. Not even in the years approaching one. Earlier.
Chronic disease does not develop in a year. It accumulates in the background of daily life, in the cellular environment, over a long time. The dementia, heart disease, diabetes, and sarcopenia now dominant in Japan’s health statistics began building in people who were in their thirties and forties — in many cases earlier. By the time the condition became visible, a significant portion of the upstream deterioration had already occurred.
This is not an argument for despair. It is the opposite. The same upstream logic that explains how chronic disease accumulates also explains how it can be slowed. The Buck Institute research shows meaningful gains in people who improve their conditions at any point — in their fifties, sixties, even seventies. Not because the past is erased, but because the cellular systems that sustain each Span remain responsive to their environment regardless of when that environment improves. Each change accumulates forward.
THE UPSTREAM PICTURE The conditions that shape the later decades of life are largely set in the decades before. NAD⁺ decline connects diet, cellular energy, repair capacity, and inflammation into a single picture — upstream of any diagnosis. The Spans Framework makes these shifts measurable before they become clinical, creating the possibility of acting while there is still the most to gain.
Even small improvements to the cellular environment may help maintain health and vitality, regardless of age. |
06 What the Oldest Okinawans
Already Knew
The researchers who came to Okinawa looking for the secret of long healthy life expected to find something rare — a special mineral in the water, an unusual plant, some hidden genetic advantage carried by the islands themselves.
What they gradually found instead was something far more fundamental.
For generations, Okinawan life had remained close to rhythms that human biology had quietly adapted to over hundreds of years — simple food, natural movement, strong social connection, moderation, purpose, and a way of living that existed in relative balance with the body rather than constant strain against it.
The dramatic rise of dementia, diabetes, cardiovascular disease, and metabolic illness across modern Japan did not appear from nowhere, nor simply from genetics. Much of it followed the gradual abandonment of those conditions after the war — accumulating silently across decades before finally appearing in the clinics.
But accumulation works both ways.
Healthspan is not determined in a single year, nor lost in one. The same body that responds slowly to years of burden can also respond slowly to years of better conditions. Which means the first step toward preserving energy, strength, clarity, and independence later in life can still begin today.
KEY REFERENCES
Zhang Y.S. & Price N.D. (2026). Bridging Wellness & Clinical Science: A Federated Healthspan Data Framework for the 21st-Century Longevity Economy. Healthspan Horizons / Buck Institute for Research on Aging.
Li Y. et al. (2018). Impact of healthy lifestyle factors on life expectancy free of cancer, cardiovascular disease, and type 2 diabetes. BMJ, 362, k2392.
Nyberg S.T. et al. (2020). Association of healthy lifestyle with years lived free of major chronic diseases. JAMA Internal Medicine, 180(5), 760–768.
Garmany A. & Terzic A. (2024). Global healthspan–lifespan gaps among 183 WHO member states. JAMA Network Open, 7(12), e2450241.
Hood L. & Price N.D. (2023). The Age of Scientific Wellness. Harvard Business Review Press.
Scott A.J., Ellison M. & Sinclair D.A. (2021). The economic value of targeting aging. Nature Aging, 1, 616–623.
Verdin E. (2015). NAD⁺ in aging, metabolism, and neurodegeneration. Science, 350(6265), 1208–1213.
Willcox D.C. et al. (2007). Caloric restriction, the traditional Okinawan diet, and healthy aging. Annals of the New York Academy of Sciences, 1114, 434–455.
Ministry of Health, Labour and Welfare, Japan. (2024). National Health and Nutrition Survey. Tokyo: MHLW.
This article is for educational and informational purposes only. It reflects published research and is not intended as medical advice. Please consult a healthcare professional for personal health decisions.
TA Medical · NMN Research Frontline · Longevity Series
