Those who exercise in their forties could prevent brain shrinkage in later life, a new study suggests.
A 20-year study found that those who lived relatively static lifestyles and had lower fitness levels aged 40 experienced a greater amount of brain shrinkage by the time they were 70 than those who were physically fit.
While the shrinkage was only small, it was enough to increase the risk of dementia and memory loss.
Using data from the Framingham Heart Study, an ongoing program following the lives of thousands of ordinary people over the course of nearly 70 years, researchers observed the fitness levels of 1,100 adults aged 40.
Participants had undergone a treadmill test followed by an MRI scan when they were 40 years old. At the time, they had no symptoms of heart disease or dementia.
Two decades later, the participants did the same test.
The researchers found that those who were in worse physical shape had higher blood pressure or a greater increase in heart rate during the tests they did in their forties. Whereas, those who were physically fit did not.
Years later, participants who rarely exercised were also found to have greater brain shrinkage - known as atrophy - than those who exercised.
Nicole Spartano, lead researcher and a postdoctoral fellow at Boston University School of Medicine, told Live Science: "If you think about each of these factors having an effect on your brain health, then the effects can really start to add up.
"The effect was not huge, but was still seen after the researchers adjusted for other factors that may affect brain health, such as high blood pressure, smoking and diabetes."
The study was published in the journal Neurology.
It's not the first piece of research to suggest a link between physical fitness and an ageing brain.
In 2012, researchers from the Center for Development of Advanced Medicine for Dementia in Japan found that adults who moved more during the day were less likely to experience progression of frontal lobe atrophy, which is the shrinking of the frontal lobe region of the brain.
This part of the brain plays a part in emotions, problem-solving, memory, judgement and personality.
Researchers concluded: "Incorporating physical activity into your daily routine can be a helpful step to prevent conditions caused by brain atrophy, such as dementia."