Being Healthy Should Not Be Enough For You

Why the next goal for you should be not just avoiding disease, but staying close to your best function for longer.

Photo by Jonathan Borba on Unsplash

I see some version of this all the time in medicine. A person in their 50s or 60s comes in; their major labs are acceptable, no new diagnoses emerge, and everyone leaves the visit with the comforting impression that things are “fine.”

But many of us know that fine is not the same as thriving. We may not have a disease, yet we recover more slowly, lose a bit of stamina, feel less sharp under pressure, and notice that our capacity is no longer what it once was. The paper I read this week gives that in-between state a name: Peakspan.

Peekspan is the period during which a person maintains at least 90% of peak functional performance in a given physiological or cognitive domain.

(Reference: Peakspan: Defining, Quantifying and Extending the Boundaries of Peak Productive Lifespan. Aging and Disease - Volume 18, Number 3, June 2027).

That idea immediately appealed to me because it captures something patients feel long before medicine has a billing code for it. The authors argue that healthspan focuses on the absence of disease and can miss the gradual erosion of function that occurs while a person is still technically healthy.

In their framework, many adults spend a large portion of their lives in a “healthy but declined” state rather than in a truly preserved peak state.

A message for readers over 50

If you are over 50, you should read this scientific article. The authors state that by age 50, a healthy person has likely already exited peakspan for many physiological functions, including fluid cognition, maximal aerobic capacity, pulmonary function, and thymic output, even though that same person may still have 20 or more years of acceptable healthspan ahead.

That should not be a reason for despair but a stimulus for action.

For years, the dominant question in preventive medicine has been, “How do we delay disease?” That remains important. But this paper asks a more ambitious and, in my view, more useful question: how do we preserve high function for longer.

As a physician, I think that is the right question for the second half of life. Most people do not wake up one day and suddenly become frail. They drift. First they lose reserve. Then they lose resilience. Then, years later, they lose independence.

The quiet gap after “normal”

What interests me most is the paper’s description of the “Peakspan-Healthspan Gap.” The authors define this as the distance between current performance and prior peak capacity, and they note that it can show up as slower reaction time, lower endurance, and greater susceptibility to novel infections long before disease is formally diagnosed.

That is exactly why so many adults feel dismissed by the phrase, “Your labs look normal.” Normal for age is not the same as optimal for you. Normal can still mean you are sliding away from your own best physiology year after year.

What peaks early, and what lasts longer

One of the most useful parts of this paper is that it treats aging as asynchronous rather than uniform.

Different systems peak at different times, decline at different rates, and matter differently for how we feel and function after 50. The authors also make clear that these are estimated peak spans based on the best available literature and proxies, not precise individualized timelines, because true life-course longitudinal data remain limited.

Start with cognition. The paper distinguishes between fluid intelligence and crystallized intelligence. Processing speed, visual-spatial reasoning, and fluid reasoning reach their apex around ages 20 to 24, while working memory peaks a bit later, around ages 25 to 29. In plain English, the mental abilities tied to speed, rapid problem-solving, and handling novel information tend to peak early and then decline gradually from early adulthood onward.

But the cognitive story does not end there. Verbal comprehension and vocabulary, which the authors place under crystallized intelligence, peak much later, around ages 45 to 54, remain relatively stable through the early 70s, and decline noticeably only around age 80.

That means many adults in midlife and early older age are no longer at their maximum speed, but may still be near their best in judgment, language, pattern recognition, and accumulated expertise.

The same early-peak pattern shows up in cardiorespiratory fitness. The paper reports that maximal aerobic capacity, maximal cardiac output, and maximal heart rate peak in late adolescence to the mid-20s, and that VO2 max then declines steadily at about 10 percent per decade.

On the respiratory side, lung function, measured by FEV1 and FVC, peaks around ages 20 to 25, while gas-exchange efficiency, measured by DLCO, shows age-related reductions that accelerate from about age 40. So a person can feel well, have no diagnosis, and still have substantially less reserve for exertion, recovery, illness, or physiological stress than they had years earlier.

Musculoskeletal aging is a little different because it offers more runway. The paper places muscle strength peak around ages 20 to 35, often with a plateau from roughly 35 to 50, while peak bone mass occurs in the 20s to mid-30s, depending on sex.

More significant declines often become obvious later, with torque and mass losses accelerating in the 60s and 70s, yet some markers begin shifting earlier, such as grip strength declining in men around the mid-40s and in women after a plateau into the mid-50s. This is one reason I see strength training not as an optional fitness culture, but as infrastructure for later life.

Kidney aging is less noticeable, but the paper suggests it begins earlier than most people realize. Renal Peakspan sits in the 20s to 30s, eGFR begins declining in the early 30s, and the rate of decline appears to steepen after about age 45. Renal plasma flow also falls beginning in the third to fourth decades, meaning kidney reserve can be eroded long before a person is ever told they have kidney disease.

Hormonal aging also follows system-specific inflection points rather than one simple script. The paper describes endocrine peakspan as largely concentrated in early adulthood, with men typically experiencing a gradual testosterone decline from mid-adulthood onward and women undergoing a more abrupt transition around menopause, with a median menopause age of 50-51.

DHEA-S and IGF-1 also decline with age, reinforcing the idea that endocrine aging is not one event but a series of shifts that can affect energy, body composition, sleep, recovery, and resilience.

Sensory and immune function deserve more attention than they usually get. The paper notes that hearing is most sensitive in the 20s, with high-frequency hearing already worsening in early adulthood, while vision often starts declining in the mid-40s, and olfaction (smell) peaks in the 20s to 30s before gradually decreasing.

On the immune side, thymic involution begins after puberty, with thymic export falling to about 20 percent of its pre-puberty level by age 25 and to about 5 percent by age 55, while naive T-cell reserves decline steadily with age.

That helps explain why resilience to infection, vaccine response, and recovery can shift meaningfully before anyone feels “old.”

What matters most here is not memorizing every age marker. It is recognizing the pattern. The capacities tied to speed, maximal output, and raw physiological reserve often peak early, while the capacities tied to knowledge, language, experience, and judgment hold up much longer.

That distinction should be encouraging for people over 50. You may no longer be at your maximum in aerobic power, reaction time, pulmonary reserve, kidney filtration, or immune robustness, but you may still be in a remarkably strong season for discernment, strategic thinking, communication, and expertise.

And this is where the paper becomes clinically useful. The authors explicitly argue that prevention and intervention should be timed to system-specific inflection points rather than applied on a one-size-fits-all schedule.

For me, that is one of the most useful ideas in the entire paper. The goal is not to become 25 again. The goal is to preserve the early-peaking capacities that keep you vigorous while continuing to leverage the later-peaking capacities that make you wise, effective, and valuable.

How does this change my mindset?

As a physician, this paper reinforces something I already believed: we should spend less time congratulating ourselves for the absence of disease and more time measuring capacity.

The authors argue that geroscience should focus on the point where a person first exits near-peak function, because that boundary may offer the greatest preventive leverage.

That means I am less interested in snapshots and more in trend lines. I want to know what is happening over time to cardiorespiratory fitness, strength, pulmonary function, renal function, cognition, and recovery, because the paper specifically frames measures such as VO2 max, grip strength, FEV1, DLCO, eGFR, and contrast sensitivity as meaningful functional endpoints for tracking decline.

This is also why I believe adults over 50 should think in terms of reserve. Build more reserve than you need. Protect more functions than you think are necessary. Because when illness, stress, surgery, grief, poor sleep, or infection arrives, the people who do best are rarely the ones who were merely “normal.” They are the ones who had something extra in their biological bank.

Do not wait for a diagnosis before starting to care about function. Do not confuse the absence of disease with the presence of vitality. And do not let the word “normal” lull you into ignoring losses that are still small enough to reverse, slow, or meaningfully delay.

As always, I encourage you to eat well (unprocessed food), do aerobic, strength, and balance exercises, and pay attention to your sleep and social contacts. This is my most important “prescription” for the rest of your life.