The greatest benefits were seen among those who were older, male and slower runners.
Researchers from University College London and Barts Health NHS Trust tracked 138 healthy people who ran the London Marathon for the first time in 2016 or 2017,
Participants had been running for less than two hours a week before they began training, mostly following a beginner's plan consisting of around three runs a week.
After six months of training, scans found major improvements in their blood pressure and arterial stiffness.
On average systolic and diastolic blood pressure dropped by 4mmHg and 3mmHg respectively.
Stiffness of the arteries indicates damage to the blood vessels, and is a key predictor of heart and circulatory problems in later life.
Arteries normally stiffen with age, but experts said exercise could reverse or limit the damage.
Among participants, some measures of arterial flexibility increased by nine per cent.
The study, published in the Journal of the American College of Cardiology, only included healthy participants.
Experts said even more benefit might be seen in those with higher blood pressure and stiffer arteries.
Lead researcher Dr Charlotte Manisty said:"Our study shows it is possible to reverse the consequences of aging on our blood vessels with real-world exercise in just six months.
"These benefits were observed in overall healthy individuals across a broad age range and their marathon times are suggestive of achievable exercise training in novice participants."
The average running time for those in the group was 5.4 hours for women and 4.5 hours for men.
Expert said this suggested a training schedule of six to 13 miles per week.
Dr Manisty said signing up for a major health challenge could be a good way to make significant changes in health.
"Making a goal-oriented exercise training recommendation – such as signing up for a marathon or fun-run – may be a good motivator for our patients to keep active.
"Our study highlights the importance of lifestyle modifications to slow the risks associated with aging, especially as it appears to never be too late as evidenced by our older, slower runners."
NHS guidance says all adults should get 150 minutes of exercise each week – such as a 30 minute brisk walk five times a week.
Commenting on the British Heart Foundation-funded study, its Associate Medical Director Professor Metin Avkiran said: "The benefits of exercise are undeniable. Keeping active reduces your risk of having a heart attack or stroke and cuts your chances of an early death.
"As the old mantra goes, if exercise were a pill it would be hailed as a wonder drug.
"Setting yourself a goal – such as training for a marathon – is a great way to stay motivated and follow through on your New Year health resolutions.
"But you don't need to train for a marathon to reap the benefits. More is usually better, but every bit counts."
