BOSTON Air pollution reduces blood flow and
interferes with the body's natural ability to break up blood
clots, researchers said on Wednesday in a finding that may help
explain why pollution can cause heart attacks.
And the study, published in the New England Journal of
Medicine, also suggests that heart patients trying to shape up
might do their exercising away from traffic.
The researchers tested 20 male volunteers, all of them
heart attack survivors, who pedaled an exercise bike while
breathing diluted fumes from the exhaust of an idling Volvo
The exposure was comparable to the pollution levels found
while driving in traffic.
Doctors already know that long-term exposure to air
pollution increases the risk of heart problems. The World
Health Organization has estimated that it causes 800,000
premature deaths worldwide each year.
The new study looked at one particularly suspect element of
air pollution and how it affected people over the short term.
Nicholas Mills of Britain's Edinburgh University and his
colleagues found that when the volunteers breathed diesel
fumes, their hearts were far more likely to be starved of
oxygen than when they were breathing clean air.
And when they tested the blood of the men, they found that
the fumes inhibited the body's natural system of breaking down
the clots that can spark a heart attack or stroke.
That may explain the results of population-based studies
showing that air pollution increases heart problems, they said.
It is not known exactly why the hearts became starved of
oxygen or which substance in the exhaust was responsible for
"The study was specific in evaluating the effects of dilute
diesel exhaust, an extremely complex mixture of particles and
gases; it is not possible to glean which constituents of diesel
exhaust were responsible for the observed effects," Dr. Murray
Mittleman, of Boston's Beth Israel Deaconess Medical Center,
wrote in a commentary.
Although the study was only done on men with a previous
heart attack, "these findings may represent the tip of an
iceberg" and apply to anyone at risk for a heart attack, he
Exercise is already known to be beneficial and it
especially decreases the risk that a person will have a heart
attack while exerting themselves, Mittleman said.
"The risk-benefit ratio may be optimized if people exercise
away from traffic when possible."