Healthy men over 50 who had finished at least five marathons in the last five years were more likely to have major calcium deposits in their arteries than healthy men who did not run as much, according to a study presented yesterday at an American Heart Association meeting in Chicago.

Calcium buildup is a sign that arteries are hardening, even when patients lack other symptoms.

“Even if you’re healthy, the more disease you have, the more likely you will, at some point later, develop a heart attack,” said the study’s author, Dr. Stefan Möhlenkamp, a cardiologist at University Clinic in Essen, Germany.

About 36 percent of the 108 male marathon runners in the study had coronary artery calcium scores above 100, possibly a sign of increased cardiovascular risk. Similar scores were seen in 22 percent of 216 men who did not run and had risk factors for heart disease similar to those of the marathon group.

Dr. Möhlenkamp said he got the idea for the study after hearing about some healthy older male runners who had heart attacks when running marathons. As a man who runs about 12 miles a week, he said, he was surprised by the possibility that long-distance running might pose heart risks.

His study looked only at calcium scores, not clinical outcomes. He and his colleagues plan to follow up with their patients for at least five years to evaluate the scores’ reliability at predicting heart problems.

Dr. Möhlenkamp cautioned that the study did not suggest that exercise is not beneficial. Rather, it seems that competitive exercise, like marathon running, may take a toll on some older athletes.

Women are less at risk, he said, because they usually develop atherosclerosis 10 years later in life than men and are less likely to be marathon runners at age 60.