VO2 Max: The One Number That Predicts How Long You’ll Live — And Most People Have Never Heard of It

I’ve been reading Andy Weir lately.

You may know him as the author of The Martian — the story of an astronaut stranded alone on Mars, keeping himself alive through relentless problem-solving and a running inventory of his dwindling resources. Weir has written two others worth your time: Artemis, set in a colony of Earthlings living on the Moon, and Project Hail Mary, which follows a lone scientist and an unlikely alien companion working together to survive the rigors of interstellar space.

What strikes me across all three books is this: none of Weir’s characters ever guesses at whether their life support is working. They constantly read the instruments. Oxygen levels, pressure readings, temperature, fuel reserves — the dashboard is not optional. It is the difference between surviving and not. The characters who ignore their readouts don’t make it to the next chapter.

I’ve been thinking about that in the context of the human body.

Because here’s the truth: your body is a life support system. It is running a continuous set of internal conditions — oxygen delivery, structural integrity, metabolic efficiency, nervous system balance — that determine whether you flourish or decline. And just like Weir’s astronauts, you have instruments available to you. Metrics that research has consistently linked to how long you live and how well.

Most people over 50 have never looked at them.

This is the beginning of a six-part series called The Numbers Don’t Lie. Over the next six weeks, we’re going to cover the five measurements that I believe every adult over 50 should know: VO2 max, grip strength, heart rate variability, bone density, and resting heart rate. Each post will explain what the metric is, why it matters, how to test it, what a good number looks like, and what to do if yours isn’t there yet. The series closes with a synthesis post that ties all five together into a personal longevity dashboard you can actually build and track.

Think of it as learning to read your own instruments.

We start today with the one that research ranks above all others.

VO2 Max: The Metric Your Doctor Rarely Checks

Your doctor checks your cholesterol. Your blood pressure. Your blood glucose. Occasionally, your resting heart rate.

Almost certainly not your VO2 max.

And yet, study after study from the Cleveland Clinic, the Mayo Clinic, and institutions in between has ranked cardiorespiratory fitness — measured by VO2 max — as the single strongest predictor of all-cause mortality. Stronger than smoking status. Stronger than diabetes. Stronger than hypertension. Stronger than cardiovascular disease history.

If there is one number that tells you how long your life support system is likely to keep running, this is it.

So what is it?

VO2 max is the maximum rate at which your body can consume oxygen during intense exercise. The “V” stands for volume, the “O2” for oxygen. It’s expressed in milliliters of oxygen per kilogram of bodyweight per minute — mL/kg/min — and it reflects the combined capacity of your lungs to take in air, your heart to pump oxygenated blood, and your muscles to extract and use that oxygen to produce energy.

In simpler terms: it’s a measure of your engine size. A high VO2 max means your body can sustain hard work efficiently. A low one means your system is straining at efforts that should feel manageable.

In Project Hail Mary, Ryland Grace wakes up alone on a spacecraft millions of miles from Earth with no memory of how he got there. The first thing he does — before he tries to remember his name, before he tries to figure out where he is — is check his instruments. Because without that data, nothing else matters. VO2 max is the instrument reading most of us have never checked. It tells you whether your body's most fundamental system — the one that captures oxygen and converts it into the energy that keeps everything else running — is operating at capacity or quietly losing ground.

Why It Matters More After 50

VO2 max declines with age. This is not optional — it happens to everyone. The research suggests a drop of roughly 10% per decade after the age of 30, with the rate accelerating after 50. By the time you reach your 70s, an untrained individual may have lost 40% or more of the cardiorespiratory capacity they had at 25.

That decline has consequences that go well beyond exercise performance. Low VO2 max is associated with increased risk of cardiovascular disease, cognitive decline, metabolic dysfunction, and early mortality. A landmark study published in JAMA Network Open found that individuals with low cardiorespiratory fitness had a risk of early death comparable to — and in some analyses exceeding — those with established heart disease.

Here is the number that I want you to sit with: men with a VO2 max below approximately 20 mL/kg/min are classified as having low cardiorespiratory fitness. That threshold, in research terms, is where risk increases sharply. Many sedentary adults over 60 are in or near that range without knowing it.

But here’s the other side of that finding, and this is the part worth underlining: VO2 max is one of the most trainable metrics on this entire list. The body responds to the right stimulus. The engine can be rebuilt.