Long-Term Marathon Running Linked With Increased Coronary Calcification

March 22, 2010

March 22, 2010 (Atlanta, Georgia) — Long-term marathon training and racing might not be as good for the heart as some runners think, a new study suggests [1]. Researchers have shown that long-term marathon runners, those who have completed at least 25 marathons over the past 25 years, have increased coronary calcium and calcified plaque volume.

"The last thing we want to see come out of this study is a suggestion that marathons are bad for you and that runners shouldn't be running them," lead investigator Dr Jonathan Schwartz (University of Colorado, Denver) told heartwire . "Running is healthy and part of a healthy lifestyle, but the data suggest that long-term marathon running, with the training that goes into them, might lead to increased levels of calcification across the lifetime."

Presenting the results of the study at the American College of Cardiology 2010 Scientific Sessions, Schwartz, along with senior investigator Dr Robert Schwartz (Minneapolis Heart Institute, MN), his father, said that at least three runners have died this year during marathons, and three runners died during the 2009 Detroit Marathon, a race that included nearly 4000 finishers. Runners are typically considered a healthy subgroup of the general population, so these deaths are usually high profile and attract a great deal of media attention. One recent estimate suggests the rate of sudden cardiac death among marathoners is rare, roughly 0.8 per 100 000 participants [2].

Metabolic and Mechanical Stress

In this study, the father-and-son team, both runners, wanted to assess coronary artery plaque in an elite group of marathon runners and compare their arteries with a control group. They identified 25 runners who completed the Minneapolis-St Paul Twin Cities Marathon every year for 25 consecutive years, thus completing a minimum of 25 marathons.

All subjects underwent coronary computed tomography angiography (CTA) using a 64-slice machine. Compared with controls, marathoners had significantly more calcified plaque volume--274 mm3 for the marathoners and 169 mm3 for the controls--and higher calcium scores and noncalcified plaque volumes, although the latter two measures did not reach statistical significance.

Robert Schwartz told heartwire that patient age, systolic blood pressure, total cholesterol, LDL cholesterol, and triglyceride levels were similar between the marathoners and controls, but heart rate, weight, and body-mass index were lower in the runners. Also, HDL-cholesterol levels were significantly higher in the runners than in the controls. The average total- and LDL-cholesterol levels were 190 mg/dL and 115 mg/dL, respectively, in the marathon runners, which suggests that diet is not is the reason for the increased calcification.

The researchers noted that the asymptomatic control group included patients undergoing CTA for clinical reasons, such as risk factors for abnormal or inconclusive stress testing, making the differences between the groups likely larger in the general population.

Asked about the possible mechanisms, Jonathan Schwartz said they don't know why the runners had more plaque in the arteries than the controls and that the findings are "counterintuitive." However, he pointed out that metabolic and mechanical stresses might be a contributing factor. For example, long-distance runners train at increased heart rates and blood pressures, as well as spend increased time in an anaerobic state, possibly leading to antioxidant damage. Also, damage to the bones might lead to calcium leaking into the bloodstream. They stressed, however, such possible explanations need to be explored further.

Next steps, according to Robert Schwartz, are studies looking at calcification in the arteries of female runners and runners who have run fewer marathons.

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