Healthspan, Lifespan, and the Decade in Between

There are two numbers that describe how long you live. Almost everyone knows the first one and almost nobody tracks the second.

Lifespan is years alive. Healthspan is years alive in good health. The World Health Organization has a formal version of the second number — health-adjusted life expectancy, or HALE — which weights each year of life by the health status of the people living it.

Subtract one from the other and you get the healthspan-lifespan gap: the number of years, on average, that a person spends alive but burdened by disease.

The gap is 9.6 years, and it is growing

In December 2024, Armin Garmany and Andre Terzic published an analysis of that gap across all 183 WHO member states in JAMA Network Open. Their findings are worth stating precisely (Garmany & Terzic, 2024):

• The global mean healthspan-lifespan gap in 2019 was 9.6 years.
• In 2000, it was 8.5 years. The gap grew by about 13% in two decades.
• The United States has the largest gap of any member state: 12.4 years — 29% above the global mean, and 24% larger than what the authors’ model projected for a country with its life expectancy.
• Women carry a gap that is a mean 2.4 years wider than men’s.

Read those numbers together and the shape of the problem appears. Medicine has been extending lifespan faster than it has been extending healthspan. The years we are adding are disproportionately years of managed illness.

We got very good at not dying. We did not get equally good at staying well.

The authors also found that the gaps track the burden of noncommunicable disease — cardiovascular disease, diabetes, cancer, neurodegeneration — rather than tracking mortality. That is the mechanism. A heart attack that would have killed someone in 1975 is now a chronic condition that someone manages for twenty years. That is a real victory in mortality statistics and a real cost in HALE.

Why the American figure is the interesting one

The US gap of 12.4 years is not simply a function of Americans living longer; several countries have higher life expectancy and smaller gaps. Garmany and Terzic describe the US gap as substantially larger than projected, underpinned by a rise in noncommunicable disease.

This is the part that should reorganize how you think about your own planning. If you are in a high-income country, your default trajectory is not “healthy until a short final illness.” Your default trajectory is roughly a decade of accumulating limitation, most of it driven by conditions with known risk factors.

The sex difference is worth sitting with too. Women live longer and spend more of those extra years in poor health. Any personal plan built on “live as long as possible” without a parallel target for function is optimizing the wrong variable.

The gap is not fixed

None of this is fatalism, and the evidence that the gap is movable is unusually strong — because the strongest evidence comes from a randomized trial rather than an observational cohort.

The Diabetes Prevention Program randomized 3,234 adults at high risk for type 2 diabetes into three arms: placebo, metformin, or an intensive lifestyle intervention targeting at least 7% weight loss and at least 150 minutes of physical activity per week. Over a mean 2.8 years of follow-up, diabetes incidence per 100 person-years was 11.0 in the placebo arm, 7.8 with metformin, and 4.8 with lifestyle (DPP Research Group, 2002).

That is a 58% reduction (95% CI, 48–66%) with lifestyle and a 31% reduction (95% CI, 17–43%) with metformin. The number needed to treat over three years to prevent one case of diabetes was 6.9 for lifestyle and 13.9 for metformin.

A number needed to treat under seven is remarkable. For comparison, many well-regarded preventive drugs sit in the dozens or hundreds. And the intervention that won was not the drug.

Diabetes is one of the main engines of the healthspan-lifespan gap. Preventing it in one of every seven high-risk people you treat is a direct, measured intervention on the gap.

Where most people are starting from

The background conditions are not encouraging. WHO reports that 31% of adults — about 1.8 billion people — do not meet recommended physical activity levels, a figure that rose five percentage points between 2010 and 2022 and is projected to reach 35% by 2030 (WHO, physical activity fact sheet). Inactivity increases in both sexes after age 60 — exactly the period when the healthspan gap opens.

So the population trend and the individual opportunity point in opposite directions. Most people are moving less as they age. The one intervention with randomized evidence for compressing the gap requires moving more.

What to do with this

• Set a healthspan target, not a lifespan target. “Live to 90” is not actionable. “Be able to carry my own luggage, get off the floor unaided, and travel independently at 80” is a specification you can train toward and test against.
• Treat metabolic health as the central lever. The DPP result is the strongest randomized evidence we have that a modifiable behavior program prevents a major driver of the gap. Weight, activity, and glucose regulation are not vanity metrics.
• Use the 7% and 150-minute figures as a floor. They are not arbitrary wellness numbers. They are the intervention targets in the trial that produced a 58% risk reduction.
• Expect the gap to arrive quietly. It is not one dramatic event. It is a decade of small functional losses that each seem tolerable in isolation. The interventions have to start before the losses do.
• If you are a woman, plan for a wider gap. The 2.4-year sex difference is a mean across 183 countries. Longer life with more disability years makes strength and function training more important, not less.

The framing that matters is this: the goal is not to add years at the end. It is to move the point at which decline begins as close as possible to the end of life. Every year you push that point back is a year subtracted from a decade that is currently, for most people, going to happen.