Straight Talk | Exercise and Cardiovascular Disease: Can Too Much of a Good Thing Become Toxic?
Substantial evidence suggests that lack of physical activity (PA) and exercise has become one of the most significant threats to health in both the United States and much of the westernized world. The federal PA guidelines suggest that all people should be getting about 30 minutes of PA on most days, or about 150 minutes of moderate or 75 minutes of vigorous PA weekly. The Institute of Medicine suggests that most people should be getting a total of 60 minutes of PA on most days.
Current statistics indicate that very few Americans are coming close to reaching these suggested levels, and this is true for most of the westernized World. In fact, my colleagues and I have published substantial data suggesting that the cause of the obesity epidemic can almost all be blamed on lack of total PA (household management and occupation-related, as well as leisure time activity).1 However, even if leisure time PA was increased enough to meet the federal PA guidelines, this would not make up for the dramatic decline noted in total PA during the last 5 decades.
On the other hand, Drs. James O'Keefe, Peter McCullough, and I, as well as others, have published several papers, getting substantial publicity in both lay and medical media, suggesting potential harm or "cardiotoxicity" with extreme endurance exercise (EEE), such as marathon running or other forms of prolonged endurance/aerobics exercise.2-4 Clearly, the major exercise problem in our society is lack of PA and exercise, not EEE.5 Nevertheless, there is a small subset of the population who are performing EEE; this group may be growing, and there are potential risks of this extreme amount of exercise.
Everything in Moderation
The potential cardiac risks of exercise have been recognized for decades. People who perform more PA and exercise have lower rates of mortality from cardiovascular disease; nevertheless, soon after vigorous aerobic exercise, the risk of sudden cardiac death (SCD) dramatically increases. In fact, even in a trained individual, the risk of SCD may increase by 2-fold after a vigorous bout of exercise, whereas the risk may increase by 10- to 50-fold in a sedentary person who performs vigorous exercise (e.g., the "couch potato" who performs heavy shoveling after the first major snowfall at the onset of winter season). This risk is markedly blunted in people who perform regular exercise. Sexual activity even increases the risk of an acute cardiac event by 2- to 3-fold in sedentary individuals, whereas the risk does not increase in fit individuals who perform regular moderate exercise.
Certainly a bout of EEE increases the risk of a cardiac event and SCD. Although this risk is real, a major paper published 2 years ago in The New England Journal of Medicine studied all marathoners in the United States from 2000-2010 and found that the risk of SCD was only about 1/200,000. Other studies, however, have suggested that the risks may be considerably higher.
Nevertheless, clearly the vast majority of marathoners do not experience any significant cardiac difficulties, suggesting to some that the potential harm of EEE may be "over-hyped." However, several well-done studies are reproducibly showing that after a marathon, close to one-third of participants have dilatation of the right-sided cardiac chambers and systolic dysfunction. Additionally, studies show that close to one-third also have significant release of cardiac troponin and brain natriuretic peptides—the same substances measured to determine evidence of acute myocardial infarction and heart failure.
Therefore, some cardiac dysfunction/transient abnormalities are present in a large number following EEE.
Bottom Line: Know Your Goals
Within days or weeks, all of these abnormalities completely resolve in most people, and, therefore, for most, this represents no major harm. However, the fact that a growing number of participants in these EEE competitions are not just doing one or two events per year, but rather are doing races many times per year—some on back-to-back weeks, and even some on consecutive days—is concerning. This amount of EEE may produce repetitive injury in some individuals or predispose some for necrosis, scarring, and a substrate from malignant ventricular arrhythmias. Additionally, the risk of atrial fibrillation seems to be increased by 3- to 5-fold in those who perform heavy exercise, and some recent evidence suggest that frequent marathoners may have more coronary artery disease.
Clearly, people who perform EEE do not typically do so to improve health, but rather they perform such activities for fun, competition, camaraderie, stress relief, and ego. Fortunately, most who perform EEE do not develop obvious complications from such activities. Nevertheless, we believe it is worth clinicians and patients recognizing that risk exists with regular performing of EEE.
Most importantly, it is important for clinicians and patients to also realize that the maximal benefits of PA and exercise training seem to occur at 35-45 minutes; efforts beyond this may burn calories, which could help prevent weight gain, as well as improve athletic performance (e.g., lower racing times), but are not likely to further improve health. As Dr. O'Keefe and I have said, "if one's goal in life is to compete in the marathon or triathlon of the Rio Olympics in 2016, this will certainly require high-intensity exercise for hours a day. But, for those whose goal is to be alive and well while watching the 2052 Olympics from the stands, then exercise and PA at lower intensities and durations would be ideal."3
1. Archer E, Lavie CJ, McDonald SM, et al. Mayo Clin Proc. 2013;88(12):1368-77.
2. O'Keefe JH, Patil HR, Lavie CJ, et al. Mayo Clin Proc. 2012;87(6):587-95.
3. O'Keefe JH, Lavie CJ. Heart. 2013;88(9):516-19.
4. O'Keefe JH, Schnohr P, Lavie CJ. Heart. 2013;99:588-90.
5. Vuori IM, Lavie CJ, Blair SN. Mayo Clin Proc. 2013;88(12):1446-61.
Carl J. Lavie, MD, is medical director of cardiac rehabilitation and director of exercise laboratories at the John Ochsner Heart and Valvular Institute at the University of Queensland School of Medicine in New Orleans. Dr. Lavie also works in the department of preventive medicine at the Pennington Biomedical Research Laboratory in Baton Rouge.
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