MINNEAPOLIS - It's impressive when someone finishes a marathon. Even more impressive, are those who run marathons year after year.

But a controversial study is raising questions about health benefits of distance running.

A Minneapolis heart doctor found that long-time marathoners have more plaque in their arteries than non-runners.

The study, published in Missouri Medicine, compared 50 men, who all ran the Twin Cities marathon 25 years in a row, to a control group of 25 non-runners, including men who were overweight, smokers or who had diabetes.

Marathon runner John Tantzen was one of the study participants.

"I thought that we were going to find that I was a very healthy person and no heart disease," he said.

But when he got his personal results from the study, "My first perception was, 'Yea! 90th percentile! Good!' And it was stunning when I read further into the details and it was 95th percentile, bad."

Cardiologist, Dr. Robert Schwartz of the Minneapolis Heart Institute at Abbott Northwestern, and Allina Health, is one of the study's authors.

"We would have expected they had less plaque because these are very fit people, typically good healthy lifestyle, lots of exercise, of course healthy eating habits. In fact, they had slightly more plaque, a big surprise," he said.

He said the results are similar to previous studies out of Germany.

Schwartz said this study did not show why the runners had more plaque, but he had some thoughts.

"If you think about it, as a person who has been running all those years, higher blood pressure, higher heart rates, metabolic by-products, very difficult situation physiologically in the context of lots of things that are going on that don't normally happen when a person is just at rest."

Tantzen thinks, for him, it's likely a family history of heart disease and diet.

"It's hard to get enough calories to train that much and it's so easy to fall into junk food," he said.

Schwartz will continue to monitor the marathon runners to see if their higher plaque affects their long-term health.

He says he doesn't think casual runners need to worry. And for now, it's too early to tell hard core marathon runners to slow down.

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