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By Heidi Splete
Researchers found surprisingly high --
and potentially dangerous -- inflammation and clotting factors
in the blood of middle-aged male runners shortly after they
completed the Boston Marathon.
None of the runners in the Boston Marathon
studies showed symptoms of actual cardiac distress. But researchers
said the presence in the runners' bloodstream of temporarily
high levels of creatine kinase-MB and C-reactive protein --
the first, a marker for muscle injury and the second, a risk
factor for clotting and heart attack -- showed they were
temporarily at increased
risk.
"C-reactive protein goes up whenever
there's muscle damage" -- whether to an overtaxed heart
or to limbs that take a pounding over a 26.2-mile marathon,
said Arthur J. Siegel, director of internal medicine at Boston's
McLean Hospital and the study's lead author.
Siegel said the increase seen in blood
clotting probably came from the skeletal muscle injury that
occurs in all marathoners who run hard enough to "hit
the wall" (become physically exhausted).
Muscle inflammation causes overproduction
of blood clotting factors such as the von Willebrand factor,
which was found in higher concentrations in the runners' post-race
samples than in their pre-race samples. High levels of white
blood cells and a protein called D-dimer also confirmed that
clotting was taking place -- a possible precursor for intravascular
thrombosis, the formation of a clot within a blood vessel.
But even if overused skeletal muscles
-- and not an overtaxed heart -- caused the excess blood clotting,
Siegel said, the chemical changes could still predispose a
runner to a heart attack. "If a coronary clot occurs,
that triggers heart muscle damage," he said.
The
bottom-line message is that regular exercise is a pathway
to cardiovascular health, but -- as with alcohol and the heart
-- you can get too much of a good thing.
Marathon running is such an example as
it transcends fitness goals, leading to a danger zone.
Starting in 1996, Siegel and colleagues
collected blood samples on the morning before the Boston Marathon
from at least 82 male marathoners -- all of them physicians
averaging 47 years old with no reported history of smoking
or heart disease.
The researchers then compared these samples
to others collected from the same runners within four hours
after the race and on the morning after.
Siegel, a former marathoner himself, said
all the study participants fit the profile of "hard core"
runners. "These runners were faster than average, experienced
and logging at least 40 to 50 miles per week. . . . They trained
hard -- harder than many mid-packers."
An accompanying study in the same cardiology
journal -- also written by Siegel -- showed that blood proteins
called troponins -- late-stage indicators of potential heart
attacks -- remained at indeterminate levels in the runners
after the marathon.
Siegel speculated that troponin levels
might be more reliable indicators of heart attack risk than
creatine kinase MB levels; testing creatine kinase MB levels,
he said, could lead to "a false positive" diagnosis
of a heart attack.
For now, he suggested, marathon runners
should take the following precautions:
- Train
smart. Take at least six months to build endurance
prior to a marathon so skeletal muscles will be ready for
a beating.
- Take your
personal medical history into account.
Runners with known heart risks should think twice about
a marathon, Siegel said.
Washington
Post October 30, 2001; Page HE01
American Journal of Cardiology October 17, 2001
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