by Gabe Mirkin, M.D.
Research evidence shows that exercise strengthens the heart, prevents and treats heart attacks and strokes, and prolongs lives (Circulation, 2018;137(18):1896-1898). The more frequently people exercise, the less likely they are to die of heart disease (JACC Cardiovasc Imaging, 2017;10:1461-1468), but there is some evidence that a person can increase heart attack risk by exercising too much (Velo News, June 13, 2019).
A few studies show that the amount and intensity of exercise done by competitive extreme-endurance athletes can be associated with:
• increased plaques in arteries leading to the heart
• increased blood levels of heart enzymes (in healthy runners with no heart damage, after a marathon), suggesting heart muscle damage (Circulation, December 3, 2018)
• irregular heartbeats such as atrial fibrillation
• scarring on hearts of ultra-endurance athletes who have no symptoms and no heart disease (J Appl Physiol, June 1, 1985;110(6):1622-6)
However, many other studies show that long-term, extreme-endurance exercise is associated with increased health:
• Olympic endurance athletes followed for up to 17 years had no evidence of any damage whatever to the size, shape and function of their heart’s main pumping chambers (left ventricles) and suffered no evidence of heart damage or disease (J Am Coll Cardiol, 2010;55(15):1619-1625).
• A review of fourteen articles on the life spans and death rates of elite endurance athletes shows that they live longer than the general population and suffer far less from heart disease (J of Sci and Med in Sport, July 2010;13(4):410-416).
• A review of 174 studies shows that ordinary exercise and more strenuous activities are associated with a lower risk of heart disease, strokes, breast cancer, colon cancer, and diabetes, and that the largest risk reductions come with increasing intensity and duration of exercise (British Med J, August 9, 2016).
Definition of a Heart Attack
A heart attack is not caused by plaque buildup on the inner lining of arteries; it is caused by a sudden complete obstruction of the blood flowing to part of the heart muscle. A 90-percent blockage of an artery does not cause a heart attack because blood can still flow through and the heart muscle can still get some oxygen.
The sudden complete obstruction of blood flow to a part of the heart muscle is usually caused by breaking off of a plaque, followed by bleeding where the plaque broke off. Then a clot forms at the bleeding site, and the clot can extend to block completely the flow of blood to the part of the heart muscle supplied by that artery. The part of the heart muscle deprived of blood flow dies and the person suffers a heart attack.
Increased Plaques in Arteries
Doctors can predict a person’s likelihood to suffer a heart attack by doing a Calcium Score, a special CT X-ray or sound wave test that measures thickness of plaques on the inner lining of arteries. Endurance athletes usually have higher calcium scores, even though they are at extremely low risk for heart attacks, because:
• their plaques contain more calcium, and
• athletes have larger heart arteries than non-exercisers.
If an athlete and a non-exerciser have the same thickness of plaque, the athlete would have a higher calcium score because he has a larger artery. However, athletes have much more stable plaques that are far less likely to break off, which can lead a heart attack (American Journal of Roentgenology, March 2015;204(3):W249-W260).
The stability of a plaque depends on how much calcium is in the plaque. Stable plaques have much thicker layers of calcium on their inner linings and that is what helps to prevent plaques from breaking off to cause heart attacks. Signs of plaque stability include extensive calcification on the inner lining of the plaque, less fat-rich areas, decreased scarring and structural changes (as seen by the pathologist interpreting the CT scan). Many studies support these findings:
• People who exercised the most had more plaques in their arteries, but suffer far fewer heart attacks and heart attack deaths than those with less heart artery calcifications (JAMA, Jan 15, 2014;311(3):271-278).
• The least active men with excessive arterial plaques were twice as likely to die of heart disease (JAMA Cardiol, Jan 30, 2019).
• Men who spent a lot of time exercising each week had more plaques than moderate exercisers, but did not suffer increased risk for heart disease (Mayo Clinic Proceedings, Oct. 16, 2017).
• Competitive older endurance athletes had the type of plaques that are far less likely to break off and cause heart attacks (Circulation, April 27, 2017;136:138-148; May 2, 2017;136:126-137).
• Older endurance athletes had wider and more dilated arteries that were far less likely to be blocked (JAMA, 2014 Jan 15; 311(3): 271-278). By comparison, more than 61.5 percent of the older men who did not exercise regularly had unstable plaques that were more likely to break off to cause heart attacks.
• Men over 60, who had run marathons for 26 to 34 years and completed 27 to 171 marathons, had plaques in their arteries that were related to their own risk factors for heart attacks and not to the number of miles or marathons they had run (Med & Sci in Sports & Ex, July 17, 2017). This suggests that plaques in arteries are not caused by endurance training, but are caused by other factors such as a pro-inflammatory diet, high blood pressure, high cholesterol or previous use of tobacco.
Elevated Heart Enzymes
Extreme exercise can raise blood levels of troponin, an enzyme that goes up in the bloodstream when a person suffers a heart attack (J Am Coll Cardiol, 2010 Jul 13;56(3):169-76). All muscles, including the heart muscle, can release enzymes into the bloodstream when they are exercised vigorously and continuously. Healthy athletes who have raised blood levels of troponin after a marathon almost never have any other markers or symptoms of heart muscle damage.
• It takes very intense exercise to raise blood levels of troponin significantly (European J of Prev Cardiology, Feb 10, 2017), and it is novice runners, rather than elite athletes, who have the greatest risk for elevated blood levels of troponin after a marathon (Circulation, December 3, 2018).
• The highest blood levels of skeletal muscle enzymes, such as SGOT, occur in people who attempt major endurance events for which they are not adequately trained.
• High blood levels of troponin after moderate exercise can be a sign of heart damage that needs medical attention (European J of Prev Cardiology, Feb 10, 02017).
Increased Risk for Atrial Fibrillation
Master athletes in endurance sports are at increased risk for developing atrial fibrillation in which the upper part of the heart starts to beat irregularly (J Atr Fibrillation, Dec 2015;8(4):1309; EP Europace, May 1, 2008;10(5):618-623). Non-exercisers with atrial fibrillation are at significantly increased risk for forming clots in the less active upper part of their hearts (called the atrium), and then the clots can travel to the brain to block the flow of blood to cause a stroke.
About twenty years ago, doctors noted that men over 80 who competed in cross country ski races longer than 100 kilometers (60 miles) were at increased risk for atrial fibrillation (BMJ, June 13, 1998;316(7147):1784-1785). Extensive studies have since confirmed this increased incidence of atrial fibrillation in healthy older world-class endurance athletes (Scan J Med & Sci in Sports, Nov 21, 2013;24(4)). However, most of these men are healthy athletes and have no obvious problems with their hearts. More detail in my report on Atrial Fibrillation – Irregular Heartbeats
Ultra-endurance athletes are at extremely low risk for heart disease and live longer than non-exercisers. Your heart attack prevention program should include both healthful eating and exercise. Since exercise helps to stabilize plaques to help keep them from breaking off from arteries, everyone should try to exercise.
Dedicated exercisers need to eat large amounts of food to meet their caloric needs, but they should still avoid red meat, processed meats, sugar-added foods, sugared drinks (except during exercise), and fried foods. If you eat a lot of those foods, you can expect to have a lot of plaques in your arteries no matter how much you exercise, and be at increased risk for having a heart attack (Journal of the American College of Cardiology, July 2017;70(4)). Check with your doctor if you have evidence of heart disease caused by a faulty diet: high blood pressure, high blood cholesterol, triglycerides, blood sugar, or CRP, an abnormal EKG, or chest pain particularly with exercise.
Caution:Intense exercise can cause heart attacks in people who have blocked arteries leading to their hearts, irregular heartbeats or other abnormalities. Heart attacks during exercise are more likely to occur when a person starts a new exercise program or increases the speed or duration of exercise. Check with your doctor.