Can too much exercise be bad for your heart?

Marathon runners
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There is certainly no doubt that exercise is good for you. To improve overall cardiovascular health, The American Heart Association recommends at least 150 minutes per week of moderate exercise (such as brisk walking) or 75 minutes per week of vigorous exercise (such as jogging) or a combination of moderate and vigorous activity. But, are there dangers in exercising too much? 

Dr. Paul Thompson, Chief of Cardiology and the Athletes’ Heart Program at Hartford Hospital, has been collaborating with scientists at the Radboud University Medical Center in the Netherlands to find an answer that question.  The group released a review of the topic in 2016 entitled “Are There Deleterious Cardiac Effects of Acute and Chronic Endurance Exercise?,” which Thompson presented while receiving an  Honorary Fellowship in the Royal College of Physicians of Ireland on Sept. 17.

The answer lies somewhere in the middle, Thompson says.

“According to epidemiological studies, when you’ve reached the Heart Association’s recommended levels, you’ve maximized the cardiovascular benefit,” says Thompson, a former elite marathoner who was a qualifier for the 1972 U.S. Olympic Marathon Trials and finished 16th in the Boston Marathon in 1976.  “Anything more than that you’re doing for some other reason—to win a race, or maybe help battle depression.”

Thompson admits it’s difficult to come to any finite conclusions about possible dangers of too much exercise because there simply aren’t enough people on the far end of the exercise curve.

“There are very few people who run for two hours a day or cycle for three hours a day.  But they do exist,” he says.

Some of the findings might be of some concern to hardcore endurance athletes.  First, Thompson says atrial fibrillation, an abnormal heart rhythm characterized by rapid and irregular beating of the atria, appears to be more common among distance runners.

“We don’t know exactly why this happens. We think it’s because exercise increases the heart chambers, and the bigger the heart chambers, the greater the chance of A Fib,” Thompson says.

Another trait found in lifelong endurance athletes is a build-up of calcium in the coronary arteries.

“Life Long endurance athletes have more calcium than we would expect.  Some have so much calcium that it looks like they have arteriosclerosis (the hardening or narrowing of the arteries),”  Thompson says.

Thompson says he’s not sure why this is but believes it might be related to the observation that exercise increases parathyroid hormone which regulates calcium levels in blood and tissues. While more calcium build-up means a greater risk for heart attack, if it’s particularly thick it can actually be more stable and protective, he says.  Calcium can be detected through a coronary calcification scan, a special X-ray to check for buildup.

“What’s interesting about these athletes is that they not only have a lot of calcium but they have a lot of dense calcium.  So, what they might actually be doing is creating safe, stable plaques in the coronary arteries. This is an important area of research and investigation,” Thompson says.

Thompson also says some endurance athletes have been found to have tiny scars where the right and left ventricle intersects.

While he expects the findings might cause alarm for some endurance athletes, Thompson says it’s too early to make any definite conclusions.

“The bottom line, endurance athletes—runners, rowers, cyclists—live longer than regular people,” Thompson says.  “It’s a chicken or the egg scenario.  Do they live longer because of the exercise or do they live longer because they were just born with better genes that make them endurance athletes? We don’t know for sure, but it’s a fun area of research and has clinical importance when taking care of endurance athletes.  I see runners and cyclists from all over the country who come here because they know of our interest in this topic.”

Learn more at the Hartford HealthCare Heart & Vascular Institute.


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