Pollution: Dangerous to Joggers

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Living in a bustling, vibrant city can certainly expose you to a lot of things, not the least of which is air pollution. Tiny particulates in the air have always been a risk for the lungs, setting off respiratory illness like asthma and emphysema, and researchers from Scotland now report that the heavily contaminated air in urban areas could also be hazardous to the heart.

Led by Dr. Nicholas Mills of the University of Edinburgh, the Scottish team found that during exercise, heart patients who inhaled as much diesel exhaust as is typically found in heavily trafficked cities (about 300 mcgs of particulate matter per cubic meter of air) increased the stress on their hearts by threefold, compared with control patients who exercised in cleaner air. In addition, patients who breathed the exhaust showed a drop in blood levels of the protein t-PA, or tissue plasminogen activator, which inhibits the formation of blood clots that can trigger heart attacks. "This suggests that patients exercising in a polluted area might be putting their heart under additional strain," says Mills, "We also found that even six hours after the one-hour exposure to air pollution, there are still adverse effects on the way blood vessels respond."

Previous studies have shown that breathing in particulates in pollution can trigger potent inflammatory reactions in the body, which can in turn lead to the destabilization of fatty plaques in heart arteries; if the plaques rupture, they can block blood flow and cause a heart attack. In addition, says Mills, because diesel exhaust particles are so small — in the nanometer range — they may be passing directly from the lungs into the blood and aggravating plaques and blood vessels. Mills chose to focus on diesel particles since diesel engines spew out as much as 100 times the pollutants as petroleum based car engines.

And he isn't the first to reveal the damaging effects of pollution on the heart. A recent U.S. study reported that exposure to polluted air boosts the risk of death from heart disease by 76%, while a trial in Germany found that heart attack rates in a group of people sitting in traffic — in a car or bus, or riding a bicycle — rose in the hour after they had been exposed to the exhaust fumes. A series of studies from countries around the world has also documented that heart attack rates are higher on days when air-pollution indices rise. "There is growing evidence that there is a relationship there," says Dr. Murray Mittleman of Beth Israel Deaconess Medical Center in Boston.

So, is jogging along a city street out of the question? Not quite. Most, but not all, studies have found a detrimental relationship between pollution and the heart. More importantly, a fear of city smog shouldn't keep you from working out. "People should exercise where and when they can," advises Mittleman. "If your only choice is exercising in a setting that is not perfectly protected from air quality, then you will probably get more benefit from exercise than risk. On the other hand, if you have a choice, it's probably better to exercise away from traffic when you can." You may not actually get anywhere on a treadmill, but at least you'll be keeping your heart safe from some extra stress.