Extreme Physical Activity Is Not a Risk Factor for Cardiovascular Death | Physician Update 2019

By Benjamin Levine, M.D., Director, Institute for Exercise and Environmental Medicine; Professor of Internal Medicine

The relationship between very high volumes of long-term physical activity (PA) and mortality is uncertain. One very small but oft-cited study from the Copenhagen City Heart Study purported to show a high mortality in “strenuous” joggers who ran “fast.” This was a study with many limitations, including that there were only two deaths of undetermined cause in their 36 strenuous joggers (maybe they were hit by a car while jogging …). Nevertheless, this paper, published in 2015 in the prestigious Journal of the American College of Cardiology, has nearly 300 citations and an Altmetrics score of 1606. Despite its flaws, it has led some authorities to argue that people shouldn’t run fast or frequently. Moreover, in two other small studies, there is evidence that endurance athletes may have more coronary artery calcification (CAC) than individuals with lower levels of physical activity. However, the largest study to date, published by our group earlier this year (N=21,758; DeFina et al, JAMA Cardiology, 2019) showed that while there was a minor increase in prevalent CAC ≥100 Agatston units in high-volume exercisers, the total CAC score, volume, and lesion number were similar compared to lower-volume exercisers. Most importantly, there was no increase in mortality (in fact, a 25-50% lower mortality depending on baseline CAC levels) in the high-volume exercisers, who on average exercised eight hours/week for many years.

Despite this reassurance, many athletes, especially those who compete in endurance events such as marathons or Ironman triathlons, exercise even more than this amount. The key question we wanted to answer with this paper was whether even higher, extraordinary levels of PA would further increase the risk of CAC and mortality.

So we dug back into the same database and identified 66 individuals (virtually twice the number in the Copenhagen study) who performed truly extraordinary amounts of exercise, >10,000 MET-minutes/week. What does this volume of exercise mean? Well, a very good competitive marathoner might run up to 105 miles per week (or 15 miles per day). If the pace was 7:30/mile for 112.5 minutes/day, their weekly MET-minutes/week would be 10,473. If the pace was even faster, say 6:30/mile for 97.5 minutes/day, their weekly MET-minutes/week would be 10,306. Thus, these athletes are doing a lot of exercise, and we figured if there was truly a danger signal, we would see it in these individuals!

So what did we find? First, we found that these athletes were indeed quite fit, as indicated by their directly measured fitness on a treadmill (this is the only database in the world in which physical activity and directly measured fitness are tracked for so long and so rigorously). Just like all the other subjects in this published cohort, they were middle-aged (mean age 53), mostly Caucasian men and generally healthy, with low rates of comorbidities. They had been training for ~30 years at ~35 hours/week. Their median CAC score was zero, and the majority (83%) had CAC scores <100, though there were some individuals with high CAC scores (the mean score was 327). After 10 years of follow-up, there were no cardiovascular deaths in this group and only two overall deaths, rates indistinguishable from others in the cohort. We concluded that very high-volume exercisers (≥10,000 MET-minutes/week; ~35 hours/week) are not at increased risk of all-cause or cardiovascular mortality. Therefore, individuals who wish to train at this level should not fear that this high-volume training will accelerate atherosclerosis in a clinically important way or increase their risk of dying prematurely.

It is important to conclude, though, that exercise is not magic, and it will not prevent the development of cardiovascular disease or death. It especially cannot overcome a lifetime of bad habits, and a healthy lifestyle (no smoking, well-balanced diet, maintaining ideal body weight) is important regardless of how much exercise you do. High-volume exercisers are strong and fit but not invulnerable. Especially if they have other risk factors for cardiovascular disease (including family history) or develop symptoms during training, they should be encouraged to visit their doctor and accept treatment for known risk factors for CV disease (hypertension, dyslipidemia, diabetes).

Read more articles from our Physician Update AHA Edition.