The 2018 Physical Activity Guidelines for Americans notes that there is no obvious “best amount” of physical activity and no evidence of increased risk, even among those that engage in high intensity activities. However, vigorous physical activity may acutely increase the risk of heart attack and sudden cardiac death in some individuals. Recent studies have shown that large volumes of high intensity physical activity may actually have maladaptive cardiovascular effects, including accelerated rates of cardiac scarring, atrial fibrillation and coronary artery calcium (CAC).
CAC is a highly specific subclinical marker of coronary atherosclerosis and is strongly associated with risk of future cardiovascular disease events, such as heart attack. The higher the CAC, the higher the risk. Traditionally, risk factors for the development of CAC (and heart disease) include high blood pressure, high cholesterol, diabetes and smoking, among others. However, the participants in the studies showing the link between high amounts of physical activity and CAC did not possess these traditional risk factors, leading to the controversial hypothesis that high levels of physical activity may actually increase CAC and subsequent risk of heart disease in otherwise healthy individuals.
In our study, published in the May 2022 issue of Medicine & Science in Sports & Exercise®, we used data from the Multi-Ethnic Study of Atherosclerosis (MESA) to better understand the relationship between physical activity, CAC and cardiovascular outcomes. MESA is a large and ongoing population-based cohort study of men and women in the United States. This cohort was ideal because it has baseline information on CAC and physical activity with roughly 15 years of follow-up data. MESA includes participants from four different racial/ethnic groups (defined as “White,” “Black,” “Chinese” and “Hispanic”), making the results of our study more broadly applicable. Physical activity was assessed via a questionnaire during the baseline exam. The physical activity data was transformed into quartiles of MET-minutes (the amount of calories expended during one minute of rest) per week, with the lowest quartile serving as the reference group for the purposes of the analyses. Computed tomography scans were done to quantify CAC, and scores were dichotomized as “low CAC” (CAC < 100) and “high CAC” (CAC ≥ 100), which correspond with low and high risk, respectively. Outcomes assessed included mortality and cardiovascular disease, defined as a composite of myocardial infarction, resuscitated cardiac arrest, definite or probably angina, fatal coronary heart disease, fatal and nonfatal stroke, other atherosclerotic death, or other cardiovascular death.
We found that participants with low CAC that engaged in the highest quartile of physical activity had a reduced risk of cardiovascular disease and mortality. Participants with high CAC that engaged in the highest quartile of physical activity had a reduced risk of mortality, and no increased risk of cardiovascular disease. In fact, high levels of physical activity were not associated with an increased risk of cardiovascular disease or mortality regardless of CAC, sex or race/ethnicity. Importantly, these results were established even after controlling for traditional risk factors.
While this study suggests that high amounts of physical activity appear to be safe, even among those at high risk, it was conducted in an observational cohort. Future studies should be done to confirm these data. Additionally, we were unable to account for differences in physical activity levels over time. However, our results should empower patients to be physically active and encourage health care providers to promote physical activity and exercise, even among those at high risk of cardiovascular disease.
Charles A. German, MD, MS, is an assistant professor and preventive cardiologist at the University of Chicago. He is the current director of cardiac rehabilitation and serves on the editorial board of the Journal of Cardiopulmonary Rehabilitation and Prevention. He also serves on the physical activity committee and obesity committee for the American Heart Association. His research interests focus on accelerometry-based physical activity; relationships between physical activity, sleep, and sedentary behavior; and the safety of physical activity in high risk populations. He can be reached at cagerman@uchicago.edu or on Twitter @DrGermanMD.
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