Running marathons could age men by as much as a decade, research suggests.
The study of males aged 40 and over who had taken part in at least 10 endurance events, found that their major arteries were far stiffer than would be expected for that age group.
Overall, men who regularly took part in events such as marathons, Ironman contests and competitive cycling were found to have a vascular age a decade older than their chronological age, which could put them at greater risk of suffering heart attacks and strokes, experts warned.
However, the study of more than 300 regular athletes found the health of women who took part in endurance events improved.
Female athletes had a vascular age that was around the same as their actual age and, by one particular measure, their vascular age was six years younger than their true age.
Scientists said the study, funded by the British Heart Foundation and Cardiac Risk in the Young, could not explain why the impacts of such events differed between men and women.
Other studies have shown that making hearts work harder to pump blood around the body can cause changes to the organ.
Researchers said that, in general, exercise reduced the risk of heart and circulatory problems and the benefits of moderate, regular activity for heart health were well known.
More research was needed to determine why endurance events might have a negative impact on male arteries, they added.
The research, which has not yet been peer reviewed, was presented at a British Cardiovascular Society conference in Manchester.
For the study, researchers from three hospitals in London studied an equal number of men and women among more than 300 “master” athletes.
They were all aged over 40 and had taken part in more than 10 endurance events while exercising regularly for at least 10 years.
Heart MRI scans were used to study the stiffness of their aortas, which carry oxygen-rich blood away from the heart to the rest of the body and the brain.
Researchers found that the aortas of the men were stiffer and, on average, the equivalent to being 9.6 years older than their chronological age.
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