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Marathon Running May
Be Risky for the Heart


NEW YORK (Reuters Health) - Some individuals may think that because exercise--and running in particular--is known to be good for the heart, marathon running must be even more heart-healthy. But findings from two new studies suggest that marathon running may actually increase one's risk of a heart attack or other cardiac event.

Contrary to the opinion of some ``hardcore recreational runners,'' marathon running is not the ``holy grail'' that provides the ultimate protection against heart disease, lead study author and former marathon runner Dr. Arthur J. Siegel of McLean Hospital in Belmont, Massachusetts, told Reuters Health.

``There is a down side--there is too much of a good thing,'' he said. ``Marathon running is an overdose that may trigger cardiac events.''

To investigate, Siegel and his colleagues studied a group of healthy middle-aged runners who participated in the 100th to 105th Boston Athletic Association Marathons that took place between 1996 to 2001.

The researchers measured levels of several proteins associated with inflammation and blood clotting in 55 finishers in the 1996 and 1997 races. Within 4 hours after the race, in comparison to before the race, levels of two of these proteins had more than doubled, Siegel's team reports in the October 17th issue of the American Journal of Cardiology.

The proteins were C-reactive protein, a marker of inflammation in blood vessels that may be associated with increased heart disease risk, and von Willebrand factor, a protein released after heart attack that has been linked to increased clotting activity and higher death risk.

Furthermore, data based on 13 finishers of the 1997 marathon show that von Willebrand factor remained elevated the morning after the race ended.

The authors note, however, that there were no heart attacks reported among the runners during the study period.

In a second study of 82 runners in the 1997 to 2001 Boston marathons, Siegel and his colleagues noted increases in various markers used to diagnose both early and late-stage injury to the heart. In fact, in two runners, elevated levels of cardiac troponin I--a protein released when heart tissue is damaged--persisted for up to 72 hours after the race ended.

The report also indicates that test results from 51 runners in 1998 to 2000 revealed that within 4 hours after the race, all of the runners again exhibited significant increases in the various markers measured as well as a 6.5-fold increase in their levels of cardiac troponin I within 4 and 24 hours after the race.

Despite this dramatic increase, however, troponin levels remained within normal range, which may indicate subtle heart injury, Siegel explained.

Levels of the enzyme creatine kinase-MB--often relied upon in emergency rooms to detect heart attack--were also significantly elevated, as in patients diagnosed with acute heart attack, Siegel said. Yet, because further tests revealed no cardiac symptoms among the runners, the increased enzyme level may have been caused by injured skeletal muscle rather than by injured heart muscle, the researcher speculated.

In light of this finding, ``on the basis of early-stage markers, runners can be overdiagnosed with heart attack,'' Siegel said in a statement.

Again, no heart attacks were seen among the runners during the study period, the investigators report.

While noting the complexity of the studies' findings, Siegel advises high-risk individuals such as those with high blood pressure, diabetes or other chronic conditions to stay away from marathon running.

Healthy individuals, in contrast, should be aware that there may be hidden risks to the sport, he said.

In addition, because the study involved competitive runners ''pushing themselves to their limit and trying to run their personal best,'' the results may not necessarily apply to non-serious runners, Siegel added.

SOURCE: American Journal of Cardiology 2001 October


Reference Source 89

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