NEW YORK (Reuters Health) - Some older marathon runners may have a greater chance of suffering a heart attack than their risk factors belie, new research suggests.

Participants run during the Riga International Marathon May 18, 2008. REUTERS/Ints Kalnins

In a study of male marathoners age 50 and up, researchers found that, despite their high activity levels, the runners were as likely as other men their age to have calcium buildup in their heart arteries.

And when compared with men who had a similar amount of heart disease risk factors, marathoners actually tended to have more calcium in their arteries.

Calcium is a component of artery-clogging plaques, and a high coronary calcium “score” -- as measured by non-invasive CT scans -- predicts an elevated risk of suffering a heart attack.

Since regular exercise is a heart-healthy habit, it’s not clear why marathoners would have calcium scores similar to those of other men their age. In general, the runners did have fewer traditional risk factors for heart disease; on average, they weighed less, had lower “bad” LDL cholesterol, higher “good” HDL cholesterol and lower blood pressure.

This raises the possibility that marathon running itself contributes to calcium buildup in some people -- but that is an unlikely scenario, according to study leader Dr. Stefan Mohlenkamp, of the West-German Heart Center Essen.

“Based on published data on the benefits of regular exercise, this possibility seems unlikely,” he told Reuters Health.

Instead, Mohlenkamp explained, the answer may rest in the formerly less-than-healthy lifestyles of some of the runners in his study. Many, he noted, had only started serious, competitive running in their 40s, and half were former smokers.

Mohlenkamp also stressed that in general, running is a good thing. “You live longer, you live better,” he said. “Our study does not question at all the proven benefits of regular exercise.”

For the study, which is published in the European Heart Journal, the researchers recruited 108 apparently healthy male marathoners age 50 and older. They calculated each man’s Framingham Risk Score -- a standard measure that doctors use to estimate a person’s risk of having a heart attack in the next 10 years. It is based on age, sex, blood pressure, cholesterol and smoking habits.

The researchers also used CT scans to calculate each runner’s coronary calcium score.

They then compared the marathoners with a group of men who had taken part in another study.

Overall, 13 percent of the marathoners had a calcium score above 400, which indicates a large of amount of plaque in the arteries, while 23 percent had scores indicating moderate plaque buildup. Those rates were nearly identical to those of the comparison group.

And when the researchers compared the runners with men who had the same Framingham Risk Score as they did, they found that the marathoners had higher rates of plaque buildup.

While regular exercise is heart-healthy, it is known that strenuous exercise can trigger a heart attack or heart-rhythm disturbance in people with pre-existing heart disease. The implication of the current findings, according to Mohlenkamp, is that conventional risk factor assessment may underestimate the heart risks of some older runners.

He said that when older adults go to their doctors asking whether such high-level exercise is safe for them, it’s important for the doctor to take a detailed risk factor history -- checking whether the patient has ever had high blood pressure or has ever been overweight, for instance.

In cases where the patient has a history of risk factors, Mohlenkamp said, it may be appropriate to do further, non-invasive testing, such as a CT scan for coronary artery calcium in addition to a stress test, which looks at the heart’s activity during exercise.

It is not generally recommended that people without heart disease symptoms undergo these cardiac tests. But Mohlenkamp said that when it comes to judging whether it’s safe for an older adult to exercise at such levels, it is “prudent” to not rely on their current risk factors alone.

SOURCE: European Heart Journal, August 2008.