WEDNESDAY, Sept. 12, 2007 (HealthDay News) -- Here's a good reason not to take your daily jog during rush hour.
Men with stable heart disease who were exposed, even briefly, to diesel exhaust fumes showed reduced blood flow to their hearts, which can increase the risk of various cardiovascular problems, including heart attacks and arrhythmias.
The levels of pollution simulated in the Scottish study were similar to those found in regular city traffic.
But don't stop running, just do it away from traffic whenever possible, advised an editorial that accompanied the study. Both articles are published in the Sept. 13 issue of the New England Journal of Medicine.
"There is substantial evidence that exercise reduces a person's lifetime risk of developing coronary heart disease, and we would encourage patients with heart disease to undertake regular exercise," said study co-author Dr. Nicholas Mills, a specialist registrar in cardiology in the Centre for Cardiovascular Sciences at the University of Edinburgh. "We would suggest, however, that wherever possible, patients avoid exercising in heavy traffic."
"This makes it clear that there's almost a switch that can turn on and off when a person is exposed to diesel fuel," said Dr. Len Horovitz, a pulmonary specialist with Lenox Hill Hospital in New York City. "Don't jog behind a bus. Don't jog in heavy traffic. If you're exercising outdoors, try to do it at a time when pollution and traffic are at their lowest level, so that would be very early in the morning or significantly into the evening when rush hour has passed."
According to background information in the study, the World Health Organization attributes some 800,000 premature deaths around the world to air pollution.
Previous research has associated short-term exposure to air pollution to cardiovascular disease and death. One study found that long-term exposure to air pollution increased the risk of death from cardiovascular disease by 76 percent. The dangers appear to be greatest with fine particulate air pollutants.
One recent study concluded that an interaction between the fine particles found in diesel exhaust and the fatty acids in LDL ("bad") cholesterol activates the genes that can cause inflammation in blood vessels, speeding up the process of atherosclerosis. Left unchecked, atherosclerosis can lead to blockage of the blood vessels.
The current study looked at 20 men, all of whom had suffered a heart attack in the past but whose heart disease was stable. All participants were exposed to diluted diesel exhaust or filtered air for one hour both while resting and while riding an exercise bike.
Heart rates increased similarly in both the filtered air and diesel exhaust sessions. But those in the diesel exhaust group had lowered blood flow to the heart. The diesel exhaust also reduced the release of endothelial tissue plasminogen activator, a "clot buster."
"We have for the first time identified ischaemic and thrombotic mechanisms to explain why there are more admissions to hospitals with angina and heart attacks on days in which the levels of air pollution are increased. No previous studies have assessed the direct effect of air pollution on blood vessel and heart function in patients with coronary heart disease," Mills said.
In the real world, the effects may even be worse.
"In real life, you have diesel fuel exposure with a background of regular air pollution, the complicating ambient air pollution," Horovitz said.
Exactly how diesel exhaust creates this change in blood flow is unclear. It's also unclear which component of diesel fuel is responsible.
"It will be important to determine the components of diesel exhaust responsible for the adverse effects on the heart and blood vessels in future work," Mills said. "We believe these effects are mediated by fine particle emissions from automobile engines. If we were able to demonstrate this, then the introduction of exhaust after-treatments to reduce particle exposure would have major benefits on public health."
There's more on air pollution at Environmental Defense.