By Gabe Mirkin, M.D.
The MARC-2 study followed 291 older men for 6.3 years with a test called Coronary Artery Calcification (CAC), and found that the amount of calcium in the arteries leading to the heart increased most in men who exercised at the highest intensity, even more than those who exercised the most (Circulation, January 4, 2023).
The authors said this showed that intense exercise increases the amount of plaques in arteries, which may be true. However, they would then have to explain why intense exercisers are far less likely to suffer heart attacks than non-exercisers (JAMA Cardiol, 2019;4(2):174-181). Exercise is prescribed both to treat and to prevent heart attacks (Front Cardiovasc Med, Feb 3, 2021;8:753672).
• CAC measures only the size of plaques. It does not measure obstruction of blood flow to the heart. Furthermore, as plaques form, the involved arteries usually widen to accommodate the plaques (JAMA Cardiol, October 27, 2021).
• Intense exercise increases the amount of calcium in plaques (Circulation, January 4, 2023). Calcium in plaques stabilizes them to help prevent plaques from breaking off, which is the cause of most heart attacks.
Heart Attacks Are Caused by Plaques Breaking Off from Coronary Arteries
Heart attacks have little to do with arteries being narrowed by plaques. A heart attack is caused by a sudden immediate complete blockage of blood flow to the heart muscle itself. First a plaque breaks off from the inner lining of an artery leading to the heart. This is followed by bleeding and clotting. Then the clot extends to block all flow of blood through that artery to deprive the heart muscle completely of oxygen, so that part of the heart muscle dies.
An X-ray test called Coronary Artery Calcification Score or Calcium Artery Score (CAC) is used to measure the size of plaques in the arteries leading to the heart. That test can also tell whether the plaques are very stable, or are unstable and more likely to break off to cause a heart attack. A stable plaque is called “hard; ” it is not full of fat and has a thick calcium periphery to keep the plaque in place. An unstable plaque is called “soft;” it is full of fat and has irregular calcium borders that may not hold the plaque in place.
Plaques are Formed from an Unhealthful Diet
Exercise does not prevent plaques from forming. A diet that is high in the pro-inflammatory foods (sweets, refined grains, sugared drinks, red meat, processed meats, fried foods, alcohol) is associated with increased risk for forming plaques (Journal of the American College of Cardiology, July 2017;70(4)). A heart-attack-preventing diet that is high in vegetables, fruits, whole grains, beans, seeds and nuts will reduce your chances of growing larger plaques. You also should avoid being overweight or smoking.
Why Exercisers May Have Higher Calcium Scores
Competitive older endurance athletes can have more plaques in their arteries than non-exercisers, and intense exercise may increase plaque formation. However, the endurance athletes are likely to have the type of plaques that are far less likely to break off to cause heart attacks (Circulation, April 27, 2017;136:138-148; May 2, 2017;136:126-137). Plaques form in arteries from an unhealthful diet and perhaps faulty genes. Exercise does not prevent plaques from forming, and a pro-inflammatory diet increases plaque formation regardless of exercise. Exercise stabilizes plaques so that they are less likely to break off to cause heart attacks. Since exercise burns lots of extra calories, exercisers may eat more food, and if they choose to add more pro-inflammatory foods, they can expect to build up more plaques.
A high Coronary Artery Calcium test (CAC) has been shown to be associated with increased risk for a heart attack, but regular exercisers may have higher CAC test results because they have more calcium in their plaques. These more stable plaques are less likely to break off and cause a heart attack. Since exercise stabilizes plaques to help keep them from breaking off from arteries, exercise should be part of your heart-attack-prevention program. You should check with your doctor about exercising if you have evidence of heart disease caused by a faulty diet: high blood cholesterol, triglycerides, sugar or CRP, high blood pressure, an abnormal EKG, or chest pain particularly with exercise.
Journal References on Coronary Artery Calcium Tests (CAC)
• CAC measures amount of plaques in a person’s arteries (J Am Coll Cardiol, 1998;31:126–33).
• CAC is an excellent predictor of likelihood to suffer a heart attack in both younger and older men (Am J Epidemiol, 2005;162:421–9; Eur Heart J, 2008;29:2782–91; J Am Coll Cardiol, 2018 Jul 24; 72(4): 434–447).
• CAC measures the size of plaques in a person’s heart arteries (J Am Coll Cardiol, 1998;31:126–33).
• Physical activity increases CAC progression (Heart, Nov 2021;107(21):1710-1716).
• Increased CAC associated with increased heart attack risk (Am J Cardiol, 2017 May 15;119(10):1584-1589).
• Life-long middle-aged male endurance athletes have high CAC scores (European Heart J, July 21, 2021;42(28):2737–2744)
Gabe Mirkin, M.D., is a sports medicine doctor and fitness guru. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin has run more than 40 marathons and is now a serious tandem bike rider with his wife, Diana. His website is http://drmirkin.com/. Click to read Gabe’s full bio.