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, recently published in JAMA Cardiology, to find the answer. Dr. Levine is a Professor of Internal Medicine and Director of the Institute for Exercise and Environmental Medicine, a collaboration between UT  Southwestern and Texas Health Presbyterian Hospital Dallas.

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, Dr. 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 for 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.

Dr. Levine studied data from the Cooper Center 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 runners, but some were cyclists, swimmers, or rowers. A subgroup of athletes trained in three of these sports.

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, Dr. Levine said.

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 Officer of The Cooper Institute and co-author of the study.

Other UT  Southwestern researchers who contributed to this work include Dr. Jarett D. Berry, Associate Professor of Internal Medicine and Clinical Sciences, and Dr. Amit Khera, Professor of Internal Medicine and Director of the Preventive Cardiology Program.