Being unfit at 40 'accelerates brain ageing'
Lack of exercise in mid-life ages the brain as well as the body, research suggests.
Being unfit at the age of 40 is linked with a smaller brain volume at 60, according to a US study.
Fitness in middle age may be particularly important for people with early signs of heart disease, say researchers at Boston University.
The study adds to growing evidence that heart health can affect brain health in later life.
The study, published in the medical journal of the American Academy of Neurology, followed 1,583 people with an average age of 40.
The participants, who did not have dementia or heart disease, took a treadmill test, followed by another two decades later, along with MRI brain scans.
"We found a direct correlation in our study between poor fitness and brain volume decades later, which indicates accelerated brain ageing," said lead researcher Dr Nicole Spartano, of the Boston University School of Medicine.
"While not yet studied on a large scale, these results suggest that fitness in middle age may be particularly important for the many millions of people around the world who already have evidence of heart disease," she added.
Dr Laura Phipps, of Alzheimer's Research UK, said: "While it's hard to conclude from these kinds of studies whether one factor definitely caused the other, the findings add to a growing body of evidence that poor cardiovascular health throughout life could have a negative effect on the brain.
"Current evidence suggests the best way to maintain a healthy brain is to keep physically and mentally active, eat a balanced diet, not smoke, drink only within recommended limits and keep diabetes, high blood pressure and high cholesterol in check."