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The research, which has not yet been peer reviewed, was presented at a British Cardiovascular Society (BCS) conference in Manchester.
For the study, researchers from Barts Heart Centre at St Bartholomew's Hospital, St George's Hospital and University College (UCL) 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.
Distance runners made up the largest group, with cyclists, swimmers, rowers also among those studied. Heart MRI scans were used to study the stiffness of their aortas, the largest artery, which carries 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.
When scientists examined the descending aorta, which runs through the chest, more significant differences were found.
For male athletes, the vascular age was found to be 15 years more than average male chronological age. However, by this measure, female athletes had a vascular age six years lower than the average for their age.