You've probably told a doctor roughly how much you exercise. Most of us round the number up a little, or guess.
The gap between what we say we do and what we actually do can be surprisingly wide.
That makes a new UK Biobank study hard to brush off.
In 46,062 adults, those with the highest measured aerobic fitness had a 24% lower risk of developing depression over the next 12.6 years, and a 17% lower risk of anxiety.
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The results were published in October 2026 in the Journal of Affective Disorders.
Instead of asking people about their workouts, the researchers put them on a cycling test and estimated VO2 max.
What VO2 max actually tells you
VO2 max is the amount of oxygen your body can use at peak effort. It is a direct, measurable marker of aerobic fitness.
Because the researchers measured it rather than asking participants to report workouts, wishful recall cannot explain the result away.
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The fittest quartile hit VO2 max values of at least 32.6 milliliters of oxygen per kilogram of body weight per minute.
The least fit sat at or below 23.8. During follow-up, 2,190 participants developed depression and 2,483 developed anxiety.
For every standard-deviation step up in VO2 max, depression risk dropped by about 10% and anxiety risk by about 6%. The link with depression was a straight line. The link with anxiety flattened at the higher end.
The study is observational, so it cannot prove fitness protects the mind. It can only show that higher fitness and lower risk tracked together across 12 years.
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How much exercise it would take
The Centers for Disease Control and Prevention recommends 150 minutes of moderate aerobic activity each week, or 75 minutes of vigorous activity, plus two days of muscle-strengthening work.
That is enough to lift most adults' VO2 max over a few months of consistent effort.
Exercise already has a track record in people who are depressed.
A 2024 network meta-analysis in the BMJ pooled randomized trials to compare different kinds of exercise with antidepressants.
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Walking or jogging produced moderate improvements in depression symptoms. SSRIs taken on their own produced smaller ones. Combining the two did better than either alone, and the authors concluded that exercise could be considered a viable alternative to drug treatment.
Earlier research has pointed the same way from a different angle. How well a 10-year-old can run has been linked to that child's mental health decades later.
Many fitness watches and gym bikes now estimate VO2 max from heart rate during activity. Checking the number gives most adults a concrete starting line before adding a weekly walk, swim or ride.
Anyone with persistent low mood or anxiety should talk to a doctor rather than treating fitness as a replacement for care.
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This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.