-New York Times Science Section 10/30/2001


Anyone who has ever run a marathon can testify to the toll it can take on the body, from painful shin splints to disabling stress fractures.

A new study suggests that long-distance running may put stresses on the body that are less obvious but potentially more dangerous. Writing in The American Journal of Cardiology, researchers say they have found evidence of temporary changes in blood chemistry in marathoners that could increase their risk of heart attack.

A team !led by Dr. Arthur Siegel of McLean Hospital, a Harvard affiliate, found that 24 hours after a marathon, runners had an increase in blood factors that cause clotting and inflammation.

Those changes alone would be unlikely to cause a heart attack, the researchers said, but could be perilous in people who also have irregular heartbeats or blockages in their coronary arteries.

The study also reported other changes in blood chemistry that could mislead an emergency room doctor into thinking that a marathon runner had had a heart attack. They detected creatine kinase-MB, which the heart produces after a heart attack, and which could lead doctors to begin unwarranted treatment. In runners, the researchers believe, the substance is released by muscles other than the heart.

The researchers said the study should not discourage people from running, which can improve cardiovascular health. But they said it should be considered when the issue is long-distance running.

Still, they noted, none of the runners whose blood was studied after they ran in five Boston Marathons had a heart problem during or after the races.