A growing body of research suggests excessive running can be dangerous

If running 15 miles a week is heart-healthy, running 45 miles a week gives you a cardiovascular system three times as clean and strong, right?

Uh, maybe not.

At least, not according to a new study that adds to a growing body of research on excessive endurance exercise.

You've heard of the runner's high. Researchers now want you to hear about runner's plaque: coronary artery plaque.

In short: Running superlong distances for many years might backfire on you.

"Years of extreme exercise efforts appear to erase some benefits you get from moderate exercise, so that your risk of heart disease, of dying of coronary disease, is the same as a sedentary person," said Dr. James O'Keefe, preventive cardiologist at St. Luke's Hospital in Kansas City, Mo.

O'Keefe said the new study found that men who were marathon runners for 25 years had 62 percent more plaque buildup in their coronary arteries than men who were sedentary but were similar to the runners in other respects, including age.

O'Keefe is co-author of the paper about the study, which appeared in the latest issue of Missouri Medicine, the journal of the Missouri State Medical Association. The study was conducted by Dr. Robert Schwartz and colleagues at the Minneapolis Heart Institute Foundation.

An unwavering advocate of exercise and its health benefits, O'Keefe said the new study adds weight to the idea that the potent benefits of exercise are "dose-dependent."

That is, the right amount matters.

Being sedentary is unhealthy. Regular, moderate exercise bestows long-term benefits. But while logging huge numbers of miles and running marathons can keep you thinner, lower your risk for type 2 diabetes and offer other benefits, it appears the subsequent wear and tear on the heart is a potential drawback, O'Keefe said.

That information might be music to the ears of 3-milers, but it's cautionary news for marathoners and ultramarathoners, at least those who have been at it for years.

"I started running in 1967, and those were the days when the police would stop you and ask you what you were running from," said Hagan, a Kansas City area ophthalmologist.

A lifelong runner, Hagan participated in more than 25 half-marathons, four marathons and two half-Ironman Triathlons. He typically ran 30 to 40 miles a week.

So he was surprised when, at age 61, he was diagnosed with atrial fibrillation, a heart rhythm problem. After learning more about runners with heart problems, he finally decided to get a heart scan for his coronary artery calcium score, an indicator of heart artery plaque.

He still felt confident that his running had provided protection. A calcium score of 100 or less is considered mild calcification, and 400 is considered extensive. His score was 1,606.

"As a physician and a runner, I felt betrayed," he said. "I thought I was out there exhausting myself, building an absolutely indestructible heart."

"Do a marathon if it's on your bucket list, when you're young," he said, "then cut way back."

Two years ago, in a report published in the journal Mayo Clinic Proceedings, O'Keefe and fellow authors cited evidence that extreme endurance training may cause structural damage to the heart, making it stiff and enlarged. That paper showed that running moderate distances two to five times a week at moderate speeds offered the best health benefits and that even 15 minutes a day of physical activity was helpful.

Eladio Valdez, coach of the Runner's Edge training group in the Kansas City area, said he is aware of recent research about the potential ill effects of years of long-distance running, and last year he held a clinic for his clients on the topic.

"I told my runners, 'We can't ignore this research,' " he said.

While such studies don't offer definitive answers yet, Valdez said, the research is "sobering," and he encourages his long-distance runners to see their cardiologist and to consider getting a heart scan.

"Moderation may be the answer in running, as with everything else in life," he said.

A runner for more than 30 years, Valdez has cut back his miles from about 40 a week to between 20 and 25. He plans to run one more marathon this fall — the 25th anniversary of his first marathon — and then no more.

"I feel I have one more in me," he said.

O'Keefe worries that some will use the findings to argue against exercise. But they would be ignoring the overwhelming evidence that being sedentary is clearly dangerous for the heart, he said.

Most people will never have the super-exercisers' issues. For every person who is overexercising, there are 19 people not getting enough exercise, O'Keefe said.