HealthSpan: How We Should Measure a Life

HealthSpan is not the years you are free of disease, because almost no one is. It is the years you stay whole, capable, and independent. That is what a health system should be built to preserve, and what it should be paid to protect.

By RaeAnn

Every piece in this series has named HealthSpan and then walked past it. The economics piece showed that no party in the Medicare Advantage chain is paid for a member’s HealthSpan. The value-based care piece argued that a plan cannot contract around it until it can measure it, and promised that the measurement question was coming next. This is that piece. I want to define HealthSpan precisely, physically and mentally and socially and clinically, show why nothing we measure today actually captures it, and then propose where measurement should begin. I will concede the hard part at the outset rather than hide it: if HealthSpan were simple to measure, someone would already be paid for it. It is not simple. It is also not impossible, and the gap between those two statements is where the opportunity lives.

But I have to start by rejecting the definition the field currently uses, because it is the reason no one can operationalize the idea. The academic literature defines HealthSpan as the years lived free of disease.¹ By that definition almost no American adult has any HealthSpan at all. Nearly half of US adults, 47.7 percent, have hypertension. Roughly one in six has diabetes, and close to another four in ten have prediabetes, most of them unaware of it.¹² If HealthSpan ends at the first diagnosis, most people lose theirs in their forties, which is not a useful measurement. It is a definitional dead end. Almost no one is disease-free. The honest question is not whether you carry a condition. It is whether you are still whole: still capable, still independent, still functional. That is what HealthSpan has to mean if it is going to mean anything a health plan can act on.

So this is the reframe the rest of the series will run on. HealthSpan is not the absence of disease; it is measured function and capacity across the whole of a life. It is the arc we should be managing end to end, and the job of a health system is to preserve that function for as long as possible and to fund only the services that measurably protect it. That last clause is the one a CFO should underline. HealthSpan is not only a clinical idea. It is a filter for deciding which health services are worth paying for at all.

Set against that standard, one number frames the failure. The gap between how long Americans live and how long they live in good, functional health runs to roughly nine years, and it has proven stubbornly resistant to the way medicine is currently practiced. Close to one-fifth of a typical life is now lived in decline.¹ We have added nearly three decades of life expectancy since the middle of the last century. We did not add three decades of health. Extending the lifespan without compressing that gap simply lengthens the years spent in decline, which is not a triumph. It is the problem HealthSpan names.

We added three decades to life. We did not add three decades of health. That difference, roughly nine years lived in decline, is the whole subject of this piece.

What We Measure Today

The words this industry uses are imprecise, and the imprecision is not harmless. Lifespan, longevity, wellness, and HealthSpan get used as if they were interchangeable, and they are not. Sorting them is the first step, because you cannot organize a system around a goal you cannot name.

Lifespan and longevity

Lifespan is the total number of years lived, measured at death, or at the population level as life expectancy.² Longevity is the same currency in a different suit: raw duration. This is the metric American healthcare has organized itself around for a century. Actuarial models, mortality tables, and most of what we call quality ultimately serve it. It is a real thing worth valuing. It is also, on its own, a blunt instrument, because it counts years without asking anything about their quality.

Wellness

Wellness, as the Medicare Advantage industry actually operationalizes it, means the annual wellness visit, the completed screening, the controlled lab value, the closed care gap. These are process and prevention measures, and CMS Star Ratings are built largely from them. They are reasonable, and I do not dismiss them. But they answer whether a service happened, not whether a life is being preserved. As I noted in the economics piece, CMS is itself moving to strip out measures it describes as tracking administrative process rather than clinical outcome, which is an admission, in the agency’s own hand, that checking the box and preserving the person are not the same thing.³

The onset of aging

Here is the idea the rest of this piece depends on. Aging is not a switch that flips at 65. It is a set of measurable declines that begin decades earlier, and they begin quietly. Fluid cognitive abilities such as processing speed and working memory peak between the ages of 20 and 30 and decline gradually from there, even as crystallized abilities like vocabulary and judgment keep improving into the fifties.⁴ Aerobic capacity and lean muscle begin their measurable decline around 30.⁵ The metric we use to trigger serious senior care, Medicare eligibility at 65, sits a full generation downstream of where the biology actually turns. We built a payment system that starts watching at the moment much of the game has already been decided.

THE DEFINITIONAL PROBLEM, STATED PLAINLY

There is no single agreed definition of HealthSpan. Some researchers end it at the first chronic disease; others at the loss of functional independence; others at a quality-of-life threshold. That lack of standardization is not merely academic. It is precisely why no payer has been able to contract around it.

The Standard takes a position: define HealthSpan by function and the onset of decline, not by the absence of death. That single choice is what makes HealthSpan measurable, and the markers later in this piece are what it makes visible.

The Limiting Factors of Aging

If HealthSpan ends when function erodes, then we should be able to name the specific ways function erodes, and roughly when each one starts. I want to organize these across the three domains the value-based care piece named as the foundation of whole-person care: physical, cognitive and mental, and social. What follows is not a comprehensive medical taxonomy. It is a list of the declines that actually end HealthSpan, chosen because each one can be measured, and each one begins earlier than the system currently looks.

Physical decline, and the hormonal clock underneath it
The earliest measurable systemic decline in the human body is hormonal, and it is worth starting there because it sits underneath so much of what follows. In men, testosterone declines by roughly one percent per year beginning in the mid-thirties, so that by the age of 50 gonadal hormone levels have commonly fallen by twenty to forty percent.⁶ In women the change is less gradual and more consequential in its timing: perimenopause commonly begins in the mid-forties, and menopause arrives on average at 51, bringing an accelerated loss of bone density and a shift in cardiovascular and cognitive risk that the care system rarely treats as the inflection it is.⁷ These are not cosmetic changes. Declining sex hormones drive muscle loss, bone loss, mood, metabolic health, and vascular function. The deep hormone decline of the forties and early fifties is, in many ways, the opening move of aging, and almost no one is measuring it as such.
On top of that hormonal foundation sit the physical markers everyone recognizes but few plans track. Aerobic capacity, measured as VO2 max, declines by roughly ten percent per decade in sedentary adults from about age 30, so that a sedentary person at 60 may have lost a quarter to a third of their peak, effectively aging their cardiovascular system decades beyond their calendar age. VO2 max is one of the single strongest predictors of all-cause mortality that we have.⁵ Muscle mass and grip strength begin declining around 30, and grip strength in particular is a cheap, validated proxy for both frailty and, strikingly, cognitive decline.⁸ Bone density erodes through midlife and then sharply for women at menopause. Gait speed, vision, hearing, and chronic pain round out the list, each one an inexpensive and powerful predictor of whether a person will keep living independently or begin the slow slide into dependence.
Cognitive and mental decline
The cognitive story is the one most likely to surprise a reader, because it runs opposite to intuition. The abilities we associate with sharpness, processing speed, working memory, fluid reasoning, peak between 20 and 30 and decline gradually from there, while the abilities we associate with wisdom, vocabulary and judgment, peak far later, around 45 to 54, and hold into the seventies.⁴ The practical implication is uncomfortable: raw cognitive speed is already declining during peak earning years, long before anyone screens for it. Underneath the visible symptoms, the biology moves earlier still. Amyloid, the protein associated with Alzheimer’s disease, can begin accumulating roughly fifteen years before any cognitive symptom appears, which reframes dementia as a disease of midlife onset and late-life diagnosis.⁴ And running through all of it is behavioral health, the depression, anxiety, loneliness, and loss of motivation that determine whether any care plan is followed at all, and which the current system carves out and hands to a separate vendor rather than treating as central.
Social decline
The third domain is the one the clinical system is least equipped to see, and it may be the most predictive. Social isolation and loneliness now carry a mortality risk comparable to established clinical risk factors, which makes them genuine HealthSpan variables rather than soft ones. The social determinants I named in the value-based care piece, housing, food, transportation, financial strain, belong here too, not as background context but as measurable inputs that determine both the onset and the pace of decline. A member who cannot afford food or reach a pharmacy is not experiencing a social inconvenience. She is experiencing an accelerant of physical and cognitive decline, and it is measurable.

How late the system actually engages

Hold all of that against the moment the system finally shows up in force. The average age at admission to hospice is about 80, yet the median hospice stay is just 17 days, which means half of all patients receive the full, coordinated benefit of end-of-life care for less than three weeks, and a substantial share die within a week of admission.⁹ The service designed to manage the close of a human life arrives, on average, at the very end of it. That is the accountability gap of this entire series compressed into a single statistic. We do not manage these transitions. We witness them, late.

The average American enters hospice at 80 and dies 17 days later. We are not managing the end of a life. We are arriving for the last two weeks of it.

Where We Should Measure, and When to Start Watching

Everything above converts into a proposal. If HealthSpan is defined by function and the onset of decline, and if the declines that matter begin decades before 65, then the redesign is not complicated to state: measure the right markers, at the right ages, early enough that the trajectory is still modifiable. The move is from reactive to proactive, from treating the event to watching the slope that leads to it.

The watch age: a range, not a birthday

I am not going to argue for a single magic number, because the biology does not support one. What the evidence supports is a watch age, a window in which lifespan management should begin in earnest, and that window opens earlier than most people expect. Hormonal decline is underway by the mid-thirties. Aerobic capacity, muscle, and bone are declining by 30. The clinical inflection for most populations, where chronic conditions begin to cluster and the deep hormone decline is well advanced, lands somewhere in the forties to early fifties. So the honest recommendation is not “start at 50.” It is: begin watching in the window where decline becomes measurable and still reversible, which for most people means the forties, and no later than the early fifties. Fifty is a reasonable default flag. The point is that 65 is indefensibly late.

CFO NOTE: WHAT A WATCH AGE DOES, AND DOES NOT, CHANGE

A watch age is not a line-of-business decision. It does not mean adding a new plan, chasing a younger segment, or restructuring who you insure. The membership is the membership.

What it changes is benefit design and wellness metrics. It means building a richer benefit design oriented to HealthSpan for members entering the watch window: earlier functional and hormonal screening, benefits that fund what actually preserves function, and wellness measures that track trajectory rather than box-completion.

The financial logic is deferral. Every chronic condition pushed from onset at 55 to onset at 65 is a decade of avoided cost and a decade of preserved risk-adjusted margin. The watch age is not a new market. It is a better-designed benefit for the market you already hold.

The markers, and the age to begin watching each

Here is the measurement scaffold: the specific markers worth tracking, when each one begins to decline, and why each matters. This is the raw material the next piece turns into contract language.

Marker	Decline / onset begins	Why it matters for HealthSpan
Testosterone (men)	~1% per year from mid-30s; 20–40% down by 50	Drives muscle, bone, mood, metabolic health; the earliest measurable systemic decline
Estrogen (women)	Perimenopause from mid-40s; menopause avg. 51	Accelerates bone loss, cardiovascular and cognitive risk at the transition
VO2 max	~10% per decade from ~30	Among the strongest predictors of all-cause mortality
Muscle & grip strength	From ~30	Proxy for frailty and cognitive decline; predicts independence
Bone density	Midlife; sharp for women at menopause	Predicts fracture, the classic cascade into permanent decline
Fluid cognition	Processing speed/memory peak 20–30	Raw cognitive speed declines during peak earning years
Hypertension	1 in 3 by 30+; earlier in Black/Hispanic adults	Onset before 55 carries the steepest mortality risk
Type 2 diabetes	Most diagnosed 45–64; earlier (46–48) in Black/Asian adults	Earlier onset is more aggressive and cardiovascular-lethal
First MI / stroke	Rising in under-50 adults	The acute event HealthSpan measurement should pre-empt
Lethal cancers	Median dx age 67 (breast 63, colon 66)	Colorectal screening already moved 50→45; the precedent exists

Two features of that table deserve emphasis. The first is that the precedent for moving measurement upstream already exists inside the system: the recommended age for colorectal cancer screening was formally lowered from 50 to 45, an explicit acknowledgment that a lethal condition was arriving earlier than the old threshold assumed.¹⁰ What The Standard proposes is simply that same logic applied across the full set of HealthSpan markers rather than one cancer at a time. The second is an equity point I do not want to pass over, because it runs directly through my own work with underserved and poly-chronic populations. Decline does not arrive evenly. Hypertension is diagnosed four to five years earlier on average in Black and Hispanic adults, with one in four diagnosed by the age of 30, and type 2 diabetes arrives earlier in Black and Asian populations than the national average.¹¹ A watch age is therefore not only a clinical and financial instrument. For the populations that enter decline earliest and with the least support, watching earlier is the difference between a decade of preserved function and a decade lost. A system that only starts looking at 65 fails these members first and worst.

This is a movement, not a fringe

None of this sits outside the mainstream of where medicine is heading. The HealthSpan-lifespan gap is now a formal field of study, mapped across nations using World Health Organization data.¹ Longevity medicine has moved from the fringe to clinical summits that reframe aging itself as a treatable condition rather than an inevitability. Functional markers that once lived only in sports science, VO2 max, grip strength, gait speed, are migrating into mainstream mortality prediction. The Standard’s contribution is not to invent these markers. It is to insist that a payer, the one party with both the data and the dollars, organize its benefit design and its wellness metrics around them, starting in the watch window rather than at the Medicare cliff.

A Question for the System, and a Vocabulary We Do Not Yet Have

I want to close on a question rather than a certainty, because I think the question is more useful than any single answer I could offer. Why are we not coached through these transitions? A person passes through puberty with at least some guidance. Then, for the next fifty years, through the hormonal turn of the thirties and forties, through perimenopause and andropause, through the first measurable losses of strength and speed and bone, through the onset of the conditions that will eventually end their independence, they are largely on their own, until one day they qualify for Medicare and the system finally turns its attention to them, often too late to change the trajectory. We have built a healthcare system that engages intensively at the very beginning of life and at the very end of it, and leaves the long, decisive middle almost entirely unmanaged. Part of the reason, I suspect, is that we lack the words. If HealthSpan is the whole managed arc of a life, the entire span across which we are trying to preserve function, then it has distinct phases, and each one deserves its own name and its own accountability. There is a BirthSpan, the period around gestation and infancy, where we already coach intensively. There is a DevelopmentSpan, childhood and adolescence, where pediatric care is organized, proactive, and plotted against a chart every parent understands. There is a VitalSpan, the long stretch of peak capacity from the twenties through the fifties, where decline quietly begins and where, today, no one is watching. And there is a PreservationSpan, the later years in which the work is to actively preserve function against decline for as long as we can. That last phase is where the instrument is missing. In the DevelopmentSpan we plot a child against a growth chart at every visit, height, weight, milestones, and a deviation from the curve triggers action. We have no equivalent for the PreservationSpan. We do not plot an adult’s function, physical, mental, social, and clinical, against an expected trajectory and act when the slope turns. We should. The growth chart proved decades ago that measuring the right things at the right ages, longitudinally and against a curve, changes outcomes. The PreservationSpan needs its own version of that instrument, and building it is the work ahead. We plot our children against a growth chart at every visit and act when the curve bends. We give our aging selves no such chart. That absence is the whole opportunity. The measurement problem, then, is not really a measurement problem. HealthSpan is not unmeasurable; it is unmeasured, because the entire apparatus of American healthcare, eligibility, quality metrics, risk adjustment, switches on at 65 and counts cost and process instead of function and trajectory. Choose the right markers, begin watching in the window where decline is still modifiable, and HealthSpan becomes as trackable as any Star measure on the books. The only thing missing is a payer willing to be paid for it, and willing to fund only the care that measurably preserves function. And naming the markers is not the same as writing them into a contract that survives an audit, resists gaming, and actually moves the capitation split. That mechanism, and its real weaknesses, is the next piece, alongside the integration of supplemental benefits, behavioral health, and pharmacy into a single whole-person strategy for the watch age and beyond.

That is the next piece in this series.

Sources

Figures are drawn from peer-reviewed literature and federal statistics. Where a range is cited, it reflects variation across the underlying studies.

Behfar A, Terzic A. Longevity leap: mind the healthspan gap. npj Regenerative Medicine (2021); and Healthspan-lifespan gap differs in magnitude and disease contribution across world regions (Nature / PubMed, 2025). The ~9-year gap, ~1/5 of life lived with morbidity, and the WHO physical-mental-social definition of health. https://www.nature.com/articles/s41536-021-00169-5
Crimmins EM and related literature; systematic review of operational definitions of lifespan, healthspan, and longevity (2025). https://foodmedcenter.org/lifespan-vs-healthspan-the-critical-gap-in-modern-aging/
CMS Contract Year 2027 Star Ratings rule-making; removal of measures CMS characterizes as administrative process rather than clinical outcome (see Article 3 of this series). https://www.cms.gov/newsroom/press-releases/cms-proposes-new-policies-strengthen-quality-access-competition-medicare-advantage-part-d
Cognitive aging literature: fluid intelligence (processing speed, working memory) peaks ~20–30; crystallized intelligence peaks ~45–54; amyloid can accumulate ~15 years before symptoms. Representative peak/onset and MCI sources. https://arxiv.org/pdf/2512.05208
VO2 max declines ~10% per decade from ~age 30 (Strait & Lakatta; Baltimore Longitudinal Study of Aging); VO2 max as a mortality predictor. https://pmc.ncbi.nlm.nih.gov/articles/PMC4968829/
Age-related hormone change: testosterone declines ~1%/year from the mid-30s; gonadal hormone levels commonly fall 20–40% by age 50. Harvard Health; peer-reviewed endocrinology reviews. https://www.health.harvard.edu/mens-health/navigating-male-menopause
Menopause occurs on average at age 51, with perimenopause commonly beginning in the mid-40s; accelerated bone, cardiovascular, and cognitive risk at the transition. https://pmc.ncbi.nlm.nih.gov/articles/PMC8020896/
Literature associating grip/hand strength with frailty and with processing speed and working memory as an inexpensive marker of decline. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3872522/
NHPCO Facts and Figures (2024) and MedPAC: average hospice admission age ~80; median lifetime length of stay ~17 days; large share of patients die within a week of admission. https://www.chionline.org/hospice-statistics/
USPSTF and American Cancer Society lowered the recommended colorectal cancer screening age from 50 to 45 for average-risk adults (2020–2021), citing rising early-onset incidence. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9402772/
Age at hypertension diagnosis by race/ethnicity, NHANES 2011–2020 (mean diagnosis 4–5 years earlier in Black and Hispanic adults; 1 in 4 by age 30); type 2 diabetes onset ~46–48 in Black/Asian adults vs later in White adults; NCI SEER median cancer diagnosis age 67. https://pmc.ncbi.nlm.nih.gov/articles/PMC9350838/
CDC/NCHS: adult hypertension prevalence 47.7% (NHANES 2021–2023, Data Brief 511); total diabetes 15.8% and prediabetes affecting roughly 38–43% of adults with over 80% unaware (CDC National Diabetes Statistics Report / NCHS Data Brief 516). https://www.cdc.gov/nchs/products/databriefs/db511.htm