Experts Ponder Whether Too Much Exercise Can Compromise Cardiovascular Health and Longevity
Physical activity was once a requirement for survival, but now many people must set aside time or make a conscious effort to incorporate it into their day, which can often be filled with hours spent in sedentary jobs and long commutes. In many cases, people need to boost physical activity levels to improve their health, but studies also are indicating that highly active patients may face health risks for taking exercise to extremes. “We need to examine the possibility that exercise is medicine and you can possibly overdose,” said Paul D. Thompson, MD, Chief of Cardiology at Hartford Hospital
Physical activity guidelines recommend that adults engage in at least 150 minutes of moderate-intensity or 75 minutes of vigorous-intensity exercise weekly. Individuals performing more than the lowest recommended dose of moderate-intensity physical activity experience added benefits, but doses >100 minutes a day do not seem to be associated with further reductions in mortality rates. A similar trend applies to more intense physical activity. “The benefits of vigorous activity are met at low doses and one does not get a lot of additional benefit when the amount of vigorous physical activity is increased much above 8 to 10 minutes a day,” said Thompson.
Although high-intensity exercise only may provide cardiovascular and longevity benefits in short doses, longer bouts can improve performance and burn calories quickly, factors that are helpful for participating in competitions and for losing or maintaining weight. “There’s no reason to discourage these motivations, but we should let patients know that there seems to be no real benefit heart-wise after a certain amount of exercise,” said Aaron Baggish, MD, Associate Director of the Cardiovascular Performance Program at the Massachusetts General Hospital Heart Center in Boston.
Studies have linked physical activity with reduced risks of not only cardiovascular diseases, but also diabetes mellitus, cancer, and dementia in a dose-dependent fashion; however, many highly active people still develop these conditions. “One of the mistakes we as cardiologists make is to think that healthy athletes who walk in are immune to health problems,” said Baggish. In fact, research suggests that high-intensity exercise may cause or accelerate coronary atherosclerosis and myocardial damage and increase the risk of sudden cardiac death, although much of this research is based on cardiac biomarkers rather than patient outcomes. “We all know that the heart is slower and that the chambers are larger in these individuals, and we assume that this is good, but increased left atrial size may increase the risk of atrial fibrillation,” said Thompson.
It has been difficult to get a sense of the potential detrimental effects of high-intensity exercise on the heart, because most population-based studies have included few individuals who exercise at levels that substantially exceed physical activity recommendations. “There is data to suggest an increased level of scar tissue in the hearts of veteran endurance athletes and that some endurance athletes may show an increased predisposition to potentially fatal cardiac arrhythmias, but the studies are based on very small numbers or in a select cohort of athletes who have presented with ominous symptoms or cardiac arrest and therefore are not necessarily representative of all endurance athletes,” said Sanjay Sharma, MD, Professor of Cardiology at the University of London. “Much more research is required in this particular field and there is ample opportunity to conduct this research given that >2 million individuals participate in a marathon in the United States each year and this figure is expected to go up by 5% per annum.”
Until more results are known, it remains unclear whether primary care physicians and cardiologists should screen or counsel athletes in ways that might be different from how they care for less active patients. “I don’t think they should necessarily be treated differently but they should be treated with knowledge of how the heart adapts to vigorous exertion over time,” said Thompson. Sharma noted that there is no evidence that very high intensity exercise carries a higher risk than moderate exercise in individuals with a normally functioning heart. “However, it is established that the risk of sudden cardiac death in an individual harboring silent cardiac disease that affects the heart muscle, the coronary arteries, or the electric system is increased by 3- to 5-fold if they engage in very high intensity exercise.”
Family history also seems to be an important modifier of athletes’ cardiovascular risks, making the history and physical a critical starting point of care. “Medical history is also important because people may lead unhealthy lives early on and then decide to exercise avidly, which is great but doesn’t negate their past behavior,” said Baggish. “We also pay a lot of attention to changes—an athlete who could easily run 10 miles but drops down to 5 is different from a person who normally runs several miles a day.” He noted that atypical symptoms and small decrements in exercise capacity may be indicators of evolving cardiovascular disease.
The issue of cardiac screening and the methods involved are controversial. Electrocardiography provides more diagnostic information than a history and physical, and, although it is an accepted method in Europe, it is not recommended by the American Heart Association for the detection of cardiovascular disease in healthy general populations of young people. “The only method of identifying high risk athletes is to perform cardiac screening, but I do concede that sudden death in sport is rare and affects only one in 50 000 and therefore nationwide screening of all young individuals is not cost-effective,” said Sharma.
There may be a variety of reasons for an individual to exercise at the extreme high end of the exercise dose spectrum, but achieving optimal health should not be one of them. Patients who choose this lifestyle should be encouraged by their physicians but should also be counseled about the risks and benefits, both cardiovascular and otherwise.
- © 2016 American Heart Association, Inc.