Both too little and too much exercise can accelerate brain aging.

In a nutshell

• Both too little and too much exercise can accelerate brain aging. The study found a U-shaped relationship where people who were sedentary and those who exercised excessively both showed signs of older-looking brains compared to moderate exercisers.
• Moderate physical activity appears optimal for brain health. People who engaged in moderate amounts of light, moderate, or vigorous exercise had the youngest-looking brains, regardless of the specific intensity level.
• This challenges the “more is always better” exercise mindset. While most people still need to move more, the research suggests there may be diminishing returns or even potential harm from extreme exercise levels when it comes to brain health.

HANGZHOU, China — When it comes to keeping your brain young, there’s a sweet spot for how much exercise you get. Get too little physical activity and your brain ages faster. Get too much, and the same thing happens.

A new study from China of nearly 17,000 people found that both couch potatoes and extreme fitness enthusiasts showed signs of accelerated brain aging compared to those who exercised in moderation. Using advanced brain imaging and wearable fitness trackers, researchers discovered what they’re calling a “U-shaped” relationship between physical activity and brain health, meaning the brain benefits peak somewhere in the middle, not at the extremes.

This research, published in Health Data Science, challenges the common belief that more exercise is always better for your brain. While we’ve long known that sedentary lifestyles are bad for cognitive health, this research suggests that excessive exercise might actually harm your brain through different biological pathways.

The research team, led by scientists at Hangzhou Normal University in China, used data from the UK Biobank, one of the world’s largest health databases. They analyzed brain scans and fitness tracker data from 16,972 adults between ages 37 and 73, with a median age of 62. About 55% of participants were women, and the vast majority (97.6%) were white.

To determine “brain age,” researchers fed over 1,400 different brain measurements into a sophisticated computer algorithm called LightGBM. This artificial intelligence system learned to predict someone’s chronological age based solely on their brain structure. When the predicted “brain age” was higher than someone’s actual age, it suggested accelerated brain aging.

Study participants wore wrist-mounted accelerometers, devices similar to fitness watches, for seven straight days to objectively measure their physical activity. The devices tracked everything from light activities like casual walking to vigorous exercise like running or high-intensity workouts.

Finding the Sweet Spot for Brain Health

Results revealed an interesting pattern across all types of physical activity. Whether researchers looked at light, moderate, or vigorous exercise, they found the same U-shaped curve: people who did very little activity showed signs of brain aging, those who did moderate amounts had the youngest-looking brains, and those who exercised excessively also showed accelerated aging.

For context, the median weekly activity levels were about 34 hours of light activity (like slow walking), 7.7 hours of moderate activity (like brisk walking), and just 20 minutes of vigorous activity (like running or intense sports). People in the highest activity quartiles were significantly more active than these medians, while those in the lowest quartiles did much less.

Brain age differences were modest but statistically significant. While the absolute differences were small, they could potentially be meaningful for long-term cognitive health, especially when considering that brain aging is linked to various cognitive disorders.

Why Exercise Extremes Might Harm Your Brain

Biological mechanisms behind this U-shaped relationship aren’t fully understood, but researchers have theories based on previous studies. For people who exercise too little, physical inactivity reduces blood flow to the brain and decreases production of brain-derived neurotrophic factor, a protein crucial for maintaining healthy neurons.

But excessive exercise presents a different theoretical problem. The researchers suggest that extreme physical activity might trigger oxidative stress and inflammatory responses in the brain, potentially accelerating the aging process, though this needs further investigation.

Brain aging also partially explained the relationship between physical activity and cognitive function. People with older-looking brains performed worse on cognitive tests and had higher rates of brain-related disorders like dementia and depression.