A new study finds that exercise that is extreme in either volume or intensity may be associated with high levels of atherosclerosis in the coronary arteries.
The study, presented in August at a meeting of the European Society of Cardiology, studied 169 veteran competitive endurance athletes against a control group of 171 relatively sedentary subjects. Compared with the control group, the study found lower levels of coronary artery calcium in athletes who ran fewer than 35 miles a week or cycled fewer than 150 kilometers a week. But athletes who ran or cycled beyond that threshold were found to harbor higher levels of coronary artery calcium than did the control group.
The study, conducted by British physicians, is certain to intensify debate over one of the most controversial questions in modern medicine: Can people exercise too much? By all accounts, exercise lowers blood pressure, helps preserve coronary-artery integrity, lengthens lifespans and otherwise promotes physical and mental health. Exercise is medicine, say public health officials.
But unlike other medication, which is generally prescribed in scientifically determined doses, exercise typically receives a blanket more-is-better recommendation. ?Most health benefits occur with at least 150 minutes (2 hours and 30 minutes) a week of moderate intensity physical activity, such as brisk walking,? says a U.S. exercise guideline. It adds: ?Additional benefits occur with more physical activity.?
Now, a small but growing number of studies suggest that the benefits of exercise may diminish or even disappear beyond a point. Some evidence suggests that the longevity benefits of endurance exercise may disappear for some extreme athletes. Other evidence shows higher-than-expected coronary artery calcification in such athletes.
Any point of diminished returns would be far beyond the physical-activity habits of the vast majority of committed exercisers. Of the 169 serious endurance athletes examined in the British study, 41 men and 16 women ran more than 35 miles or cycled more than 150 kilometers a week, said Ahmed Merghani, a cardiology resident who led the study. The senior author of the study was British sports cardiologist Sanjay Sharma, medical director for the London marathon. The study is yet to be published.
Besides distance, the study found an association between coronary calcium levels and exercise intensity. Compared with the control group, the study found significantly lower levels of coronary calcium in the slowest men and women. In women, those levels rose as speed increased, though not to the levels of the relatively sedentary control group. The fastest men, however, had significantly higher levels of coronary calcium than did men in the control group.
Yet within the bad news for extreme endurance athletes the study also found good news. The type of plaque found within the heavy exercisers was dense as opposed to soft, and recent research has shown that dense plaque is less likely to rupture and cause a heart attack or stroke. ?It is remarkable that the athletes in the Sharma study have less non-calcified plaque (the plaque that ruptures and causes heart attacks) than the non-athletes,? Benjamin D. Levine, a cardiology and exercise-science professor at University of Texas Southwestern Medical Center Dallas, said in an email.
Even so, plaque-free arteries are the ideal, and Dr. Merghani pointed out that even dense plaque can narrow arteries in a way that can pose danger during heavy exertion.
?It?s a very important study,? said Paul Thompson, a veteran marathoner who is chief of cardiology at Hartford Hospital in Connecticut. ?It confirms prior reports of possible increased coronary calcium with increased amounts of exercise, implying more atherosclerosis. But it showed more calcified plaque, at least in male runners. Calcified plaque is probably more stable, less likely to rupture and thereby to cause heart attacks and sudden death.?
The British researchers recruited volunteers for the study via advertisements in athletic magazines. The 169 athletes chosen for the study were older than 40, had engaged in competitive endurance exercise for more than 10 years and were free of cardiovascular risk factors such as family history of heart disease. The control group was also older than 40 and free of cardiovascular risk factors, and its members exercised less than 150 minutes a week. The researchers used CT coronary angiograms to determine calcium scores and also identify the nature of the plaque found within those arteries.
Researchers speculate that potential causes of greater coronary calcium in extreme athletes could be inflammation, changes in the structure of the heart or an excess secretion of certain proteins or hormones. ?It is true that exercise may increase parathyroid hormone levels, and thus MAY increase vascular calcification,? acknowledged Dr. Levine wrote in an email.
But Dr. Levine argues that substantial research supports a more-is-better mentality. Aging ?athletes have youthful, compliant (flexible) hearts and large blood vessels that have a biological age more than 25 years ?younger? than their chronological age compared with their healthy but sedentary counterparts,? said Dr. Levine.
Other studies, along with the sudden deaths of famous runners such as Micah True, give other cardiologists pause. ?Chronic excessive strenuous exercise can exact a toll on the durability of the cardiovascular system, on how well the pump holds up through the decades,? says James O?Keefe, a Kansas City cardiologist.
Most cardiologists are awaiting more research. ?We know that there is some point where we reach diminishing returns? from exercise, says Clyde W. Yancy, a Northwestern University cardiologist. But ?it remains very unclear? whether exercise at some point poses danger.
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