The Longevity Number Your Doctor Probably Never Mentions
Your cardiovascular fitness level may predict how long you live better than almost any other single measurement — here's what that means for you.
You probably know your blood pressure. Maybe your cholesterol. But there's one number that researchers say may be an even stronger predictor of how long you'll live — and most people have never heard of it. It's called VO2 max, and it's simpler to understand than it sounds.
What Is VO2 Max, Exactly?
VO2 max is a measure of how much oxygen your body can use during intense exercise. The higher your VO2 max, the more efficiently your heart, lungs, and muscles work together to keep you going.
Think of it as your engine size. A bigger, more efficient engine can handle more demand — and it tends to last longer.
It's traditionally measured in a clinical or sports performance setting, where you exercise to your limit while wearing a mask that analyzes the air you breathe in and out. But newer research suggests that estimated VO2 max — calculated from simpler tests or wearable devices — can also provide meaningful information.
Why Researchers Think It Predicts Longevity
A landmark study published in JAMA Network Open followed more than 750,000 U.S. veterans and found that low cardiorespiratory fitness was the strongest predictor of death from any cause — stronger than smoking, diabetes, or heart disease. The least fit individuals had roughly five times the risk of dying compared to the most fit group.
A separate large-scale review published in the European Heart Journal found that each meaningful increase in VO2 max was associated with a significant reduction in the risk of dying from cardiovascular disease and from all causes combined.
It's important to note that most of this research is observational — it shows a strong association between fitness and longevity, but can't prove that improving your VO2 max directly causes you to live longer. Still, the consistency of the findings across large populations is hard to ignore.
What's Considered a Healthy Number?
VO2 max is measured in milliliters of oxygen per kilogram of body weight per minute (ml/kg/min). The numbers vary by age and sex, so what's "good" for a 65-year-old woman is different from what's good for a 45-year-old man.
As a general reference, the American Heart Association classifies cardiorespiratory fitness into five categories ranging from low to elite. Most adults in average health fall somewhere in the middle. The good news: research consistently shows that moving from the low category to even a moderate fitness level produces some of the biggest gains in health outcomes.
You don't have to become an athlete to benefit. Getting out of the bottom tier may matter most.
How to Get a Sense of Your Own VO2 Max
A formal VO2 max test requires lab equipment and isn't something most doctors routinely order. But there are practical ways to get an estimate.
- Wearable fitness trackers from brands like Garmin, Apple, and Fitbit now estimate VO2 max based on heart rate and activity data. These are not clinical measurements, but research suggests they can be a reasonable proxy.
- The Rockport Walk Test is a simple field test: walk one mile as fast as you can on a flat surface, record your time and heart rate immediately after, and plug the numbers into a published formula to estimate your VO2 max. It's free and requires no equipment.
- Talk to your doctor. If you have cardiovascular risk factors or are starting a new exercise program, ask about a formal exercise stress test, which can provide more detailed information about your heart and fitness level.
Can You Actually Improve It?
Yes — and this is where the research gets genuinely encouraging. VO2 max is not fixed. Studies consistently show it responds to aerobic exercise training, even in older adults.
Research published in Mayo Clinic Proceedings found that high-intensity interval training (HIIT) — short bursts of harder effort followed by recovery — produced significant improvements in VO2 max across age groups, including adults over 65. Steady-state aerobic exercise like brisk walking, cycling, and swimming also improves it, just more gradually.
The key is consistency. Even modest improvements in cardiorespiratory fitness have been linked to meaningful reductions in health risk in the research literature.
Practical Steps You Can Start This Week
You don't need a trainer or a lab to start moving the needle. Here are research-supported strategies worth discussing with your doctor:
- Add one or two interval sessions per week. Try alternating one minute of faster effort with two minutes of easier pace during a walk or bike ride.
- Build your aerobic base. Aim for at least 150 minutes of moderate-intensity aerobic activity per week, as recommended by the American Heart Association.
- Don't underestimate walking. For people who are currently sedentary, even regular brisk walking has been shown to improve cardiorespiratory fitness.
- Track your progress. If you use a wearable device, monitor your estimated VO2 max over weeks and months as a rough gauge of improvement.
Before making significant changes to your exercise routine — especially if you have heart disease, high blood pressure, or other health conditions — talk with your doctor first.
The Bottom Line
VO2 max may be the most powerful health number most people have never checked. Large, long-term studies suggest that low cardiorespiratory fitness is one of the strongest predictors of early death — and that improving your fitness level, at any age, is associated with better health outcomes. You don't need to run a 5K or hit the gym every day. Start where you are, move a little more than you did yesterday, and talk to your doctor about what's right for you.
