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Calcified plaques show up more often in endurance athletes but without a link to mortality, according to an observational study with over a decade of follow-up.

Compared with the less physically active, men with over 3,000 metabolic equivalent of task (MET)-min of exercise per week were more likely to have clinically significant coronary artery calcification (CAC) of 100 Agatston units or more (RR 1.11, 95% CI 1.03-1.20).

Yet even highly active men with that much CAC had no worse odds of mortality over 10.4 years than sedentary men performing less than 1,500 MET-min of weekly exercise (adjusted HR 0.77, 95% CI 0.52-1.15), reported Benjamin Levine, MD, of Texas Health Presbyterian Hospital in Dallas, and collaborators of the Cooper Center Longitudinal Study.

Heavy exercisers without significant CAC actually had about half the mortality risk seen in their least-active counterparts (adjusted HR 0.52, 95% CI 0.29-0.91) in the study published online in .

"These results do not support the contention that high-volume endurance activity, with a mean of more than 1 hour of activity per day, increases the risk of all-cause or CVD [cardiovascular disease] mortality, regardless of CAC level," Levine's group said. "Our findings should reassure patients and their health care professionals that it appears these highly active individuals can safely continue their exercise programs."

On the other hand, people with CAC scores >100 AU should get more intense lipid intervention and other preventive therapies even if they are highly active, Chip Lavie, MD, of the John Ochsner Heart and Vascular Institute in New Orleans, and colleagues argued in an invited commentary.

"We would still advocate consideration for CAC testing in high-volume exercisers who have intermediate coronary risk profiles, with consideration for exercise testing in those with very high levels of CAC ... at least to rule out severe ischemia and malignant arrhythmias," they wrote.

Study participants were patients visiting the Cooper Clinic in Dallas from 1998 to 2013. They were healthy men who reported their physical activity level on a questionnaire and underwent CAC scanning at a mean age of 51.7 years (n=21,758).

Patient outcomes were extracted from the National Death Index Plus.

Due to an insufficient number of deaths, women were excluded. The all-male study cohort was also generally white and educated, which further limited the generalizability of findings, investigators acknowledged.

They showed that the most active group (>3,000 MET-min/week) actually netted more than 4,600 MET-min per week on average -- the equivalent of running 6 miles a day at a 10-min mile pace, Levine and colleagues noted. Among those athletes, the ones classified as having at least 100 AU in CAC actually averaged 807 AU.

Half of the heavy exercisers confirmed at 5 years that they were still working out to the tune of at least 1,500 MET-min/week.

At the other end of the exercise spectrum were those who performed less than 1,500 MET-min of exercise per week. These sedentary individuals were especially likely to die during follow-up if they had CAC of 100 AU or more (adjusted HR 1.93, 95% CI 1.34-2.78).

"Although clearly a low level of physical activity is a much greater concern for society than very high and even extreme levels, concern has been raised about the potential harm of extreme levels of exercise," according to Lavie and fellow editorialists.

"This concern includes the release of cardiac troponin and brain natriuretic peptides and cardiac dilatation and dysfunction after very extreme bouts of exercise ... which may lead to cardiac fibrosis and increased risk of serious dysrhythmias. In addition, heavy physical activity and exercise has been recognized to promote coronary artery calcification," they continued.

That heavy exercise appears safe may be attributed to calcific atherosclerosis being more stable than soft, non-calcified plaques, as well as a better CVD risk profile among highly-active people, Lavie's group speculated.

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