05/23/2010 05:12 am ET | Updated May 25, 2011

Endurance Running and Heart Damage: Making the Case for Moderation Not Marathons

On the heels of the LA Marathon, the 26.2 mile race signifies the feat of mind over body - the ability to mentally overcome the pain or discomfort of the long distance run. But if you were a compulsive marathoner, would you change your behavior if you knew too much training could put you at risk for heart problems like higher blood pressure and heart attack?

One might assume if regular moderate cardiovascular exercise is good for your heart, then loads of it must be great for you, right? Hmmm. Herein lies a most ironic dichotomy.

The leading health-related cause of death for men and women in the U.S. is heart disease, according to the American College of Sports Medicine. But get in good cardiovascular shape with plenty of exercise and your risk of cardiovascular disease can drop as much as 50% in men, according to research published by Myers and colleagues in the December 2004 issue of The American Journal of Medicine. Furthermore, burning a total of 1,000 calories a week through exercise is associated with a 20% reduction in mortality in men. As for women, a major lifestyle study from the Department of Nutrition at the Harvard School of Public Health and Brigham and Women's Hospital showed that compared to lean, physically active women, there was nearly a two and half-fold increase in risk of death for obese and inactive women. This was reported in the December 23, 2004, issue of The New England Journal of Medicine.

None of this is surprising to you, right? Here's the interesting part. A new study, albeit a small study, suggests that too much exercise may lead to increased stiffness of the large arteries, which in turn, can lead to high blood pressure, which can impair the heart, possibly even causing a heart attack and death. Wow.

The study, led by Despina Kardara from the Athens Medical School and Hippokration Hospital in Athens, found that the intense training people do for marathons may be causing too much stress on the heart. He explained that, "the cardiovascular system is like a sports car engine. If you do not use it, it will decay, but if you run it too fast for too long, you might burn it out."

Despina says, "our data suggest that exercise may have an inverted U-shape relation with arterial stiffness. In other words, when you do not exercise you have higher risk of cardiovascular events, but the same also happens when you exercise too much." The findings were presented on March 13th at the American College of Cardiology's annual scientific session in Atlanta. The researchers said this was the first study that examined the long-term effect of intense, protracted endurance training on the elastic properties of the large arteries.

The test conducted by scientists evaluated the blood pressure levels and flexibility of the arteries in 49 people who were marathoners (mostly men). These runners trained about 10 to 19 hours a week over a span of about two years to 20 years. They were compared to a group of 46 people of similar age, height and cardiovascular risk factors but who were not endurance athletes. The results showed the runners had higher blood pressure and reduced heart rate. And, of those runners, the ones who trained more intensely were the ones who showed more stiffness in their arteries. Only seven of the runners were women.

One explanation offered by a co-investigator for the study is that the extreme exercise done by marathon runners may place repeated and excessive stress on the artery wall, leading to its fatigue and causing the arteries to stiffen.

I suspect the intriguing results of this study will lead to further research.

As a fitness professional, I am not at all advocating that people stop working out or training. However, If you're an endurance junkie training like a wild banshee, you maybe want to tone it down a notch, turbo -- Kadara advises endurance athletes to be cautious about the amount and volume of their training programs, not to wear yourself out and to work closely with your physician especially if you're doing an event like a marathon.