For the past decade or so, there’s been increasing concern that high-volume, high-intensity exercise could injure the heart. A large US study found that in middle-aged men, extreme exercise did not raise the risk for cardiovascular or all-cause mortality, even with elevated coronary calcium, a footprint of atherosclerosis.
Exercise is often cited as the best preventive medicine, but how much is too much for the hearts of middle-aged athletes? Sports cardiologist Dr Benjamin Levine led a study to find the answer. Levine is a professor of internal medicine and director of the Institute for Exercise and Environmental Medicine, a collaboration between UT Southwestern Medical Centre and Texas Health Presbyterian Hospital Dallas.
Coronary calcium scanning is an imaging test that helps physicians classify patients without cardiac symptoms as low, intermediate, or high risk for heart attack. It represents how much calcium (and thus cholesterol deposits) has accumulated in the blood vessels that supply the heart. The scan can help physicians determine the need for medication, lifestyle modification, and other risk-reducing measures.
“The question has never been whether exercise is good for you, but whether extreme exercise is bad for you. For the past decade or so, there’s been increasing concern that high-volume, high-intensity exercise could injure the heart. We found that high volumes of exercise are safe, even when coronary calcium levels are high,” Levine said.
High-volume, high-intensity exercise was defined in this study as at least five to six hours per week at a pace of 10 minutes per mile. The average amount of high-intensity exercise in this group was eight hours per week.
Coronary calcium is a footprint of atherosclerosis, a disease in which plaque builds up in the arteries and gives rise to heart attack and stroke. When coronary calcium is detected in the heart, the clogging process within the blood vessels has begun. The majority of high-intensity athletes had low levels of coronary calcium, though their odds of having higher levels were 11 percent greater than men who exercised less. Most importantly, the researchers found that higher calcium scores did not raise the high-intensity athletes’ risk for cardiovascular or all-cause mortality.
Levine studied data from the Cooper Centre Longitudinal Study. A total of 21,758 generally healthy men ages 40 to 80 and without cardiovascular disease were followed for mortality between 1998 and 2013. The athletes, a majority of them in middle age, reported their physical activity levels and underwent coronary calcium scanning. Most were predominantly runners, but some were cyclists, swimmers, or rowers. A subgroup of athletes trained in three of these sports.
Women were not included in the study as their mortality rates are lower than for men.
Despite the findings that extreme exercise does not raise heart disease risk, Levine advises against using the protective effect of exercise to excuse poor lifestyle habits. “You cannot overcome a lifetime of bad behaviours – smoking, high cholesterol, hypertension – just from doing high levels of physical activity, so don’t use that as a magical cure,” said Levine, who holds the distinguished professorship in exercise sciences at UT Southwestern.
He also recommends caution when starting a new training programme. “If you want to train for a marathon, you have to have a long-range plan to build up slowly before you achieve those volumes and intensity of exercise.”
“The known benefits of regular physical activity in the general population include decreased mortality, heart disease, diabetes, and many other medical conditions which reminds us how important it is participate in regular physical activity as recommended by the 2018 Physical Activity Guidelines,” said Dr Laura DeFina, chief scientific pfficer of The Cooper Institute and co-author of the study. “The current study shows no increased risk of mortality in high-volume exercisers who have coronary artery calcium. Certainly, these high-volume exercisers should review their cardiovascular disease risk with their primary care doctor or cardiologists and the study results provide helpful clinical guidance.”
“The most important take-home message for the exercising public is that high volumes of exercise are safe. The benefits of exercise far outweigh the minor risk of having a little more coronary calcium,” Levine said.
Importance: Few data are available to guide clinical recommendations for individuals with high levels of physical activity in the presence of clinically significant coronary artery calcification (CAC).
Objective: To assess the association among high levels of physical activity, prevalent CAC, and subsequent mortality risk.
Design, Setting, and Participants: The Cooper Center Longitudinal Study is a prospective observational study of patients from the Cooper Clinic, a preventive medicine facility. The present study included participants seen from January 13, 1998, through December 30, 2013, with mortality follow-up through December 31, 2014. A total of 21 758 generally healthy men without prevalent cardiovascular disease (CVD) were included if they reported their physical activity level and underwent CAC scanning. Data were analyzed from September 26, 2017, through May 2, 2018.
Exposures: Self-reported physical activity was categorized into at least 3000 (n = 1561), 1500 to 2999 (n = 3750), and less than 1500 (n = 16 447) metabolic equivalent of task (MET)–minutes/week (min/wk). The CAC scores were categorized into at least 100 (n = 5314) and less than 100 (n = 16 444) Agatston units (AU).
Main Outcomes and Measures: All-cause and CVD mortality collected from the National Death Index Plus.
Results: Among the 21 758 male participants, baseline mean (SD) age was 51.7 (8.4) years. Men with at least 3000 MET-min/wk were more likely to have prevalent CAC of at least 100 AU (relative risk, 1.11; 95% CI, 1.03-1.20) compared with those accumulating less physical activity. In the group with physical activity of at least 3000 MET-min/wk and CAC of at least 100 AU, mean (SD) CAC level was 807 (1120) AU. After a mean (SD) follow-up of 10.4 (4.3) years, 759 all-cause and 180 CVD deaths occurred, including 40 all-cause and 10 CVD deaths among those with physical activity of at least 3000 MET-min/wk. Men with CAC of less than 100 AU and physical activity of at least 3000 MET-min/wk were about half as likely to die compared with men with less than 1500 MET-min/wk (hazard ratio [HR], 0.52; 95% CI, 0.29-0.91). In the group with CAC of at least 100 AU, men with at least 3000 MET-min/wk did not have a significant increase in all-cause mortality (HR, 0.77; 95% CI, 0.52-1.15) when compared with men with physical activity of less than 1500 MET-min/wk. In the least active men, those with CAC of at least 100 AU were twice as likely to die of CVD compared with those with CAC of less than 100 AU (HR, 1.93; 95% CI, 1.34-2.78).
Conclusions and Relevance: This study suggests there is evidence that high levels of physical activity (≥3000 MET-min/wk) are associated with prevalent CAC but are not associated with increased all-cause or CVD mortality after a decade of follow-up, even in the presence of clinically significant CAC levels.
Laura F DeFina, Nina B Radford, Carolyn E Barlow, Benjamin L Willis, David Leonard, William L Haskell, Stephen W Farrell, Andjelka Pavlovic, Katelyn Abel, Jarett D Berry, Amit Khera, Benjamin D Levine