SEPTEMBER / OCTOBER 2005

AROUND HARVARD

This article originally appeared in the August 2005 Harvard Heart Letter and is provided courtesy of
Harvard Health Publications.

Air pollution: Particularly offensive to the heart

Tiny particles from traffic and industry, along with other pollutants, can trigger heart attacks and spur the development of heart disease.

Air pollution isn’t just a problem for the lungs. It turns out to be just as bad — if not worse — for the heart and circulatory system. Pollutants in the air can trigger heart attacks, strain already troubled hearts, and even pave the way for cholesterol to clog arteries.

This shouldn’t come as a surprise. After all, the very direct type of air pollution known as cigarette smoking has both immediate and long-term effects on the hearts and blood vessels of smokers and the people who live and work with them. But just as it took several decades to make the connection between heart disease and smoking, it has taken a while to forge a solid link with air pollution. Although more work needs to be done, the evidence is strong enough to prompt the American Heart Association to call for stronger air quality standards as one route to reducing heart disease.

Burrowing in
Depending on your size and activity level, you inhale between 3,000 and 6,000 gallons of air each day. “Fresh air” is mostly pure nitrogen and oxygen, with a smattering of argon, carbon dioxide, and other gases. There’s dust, too, as well as mold spores and pollen.

Manufacturing, transportation, electricity generation, and other human activities spew a bewildering array of pollutants into the air. Gases such as nitrogen and sulfur oxides, carbon monoxide, and ozone are common pollutants. So are tiny particles from car and truck exhausts, chimneys and smokestacks, and chemical reactions between gases. Some of these particles are so small that 100 could sit side-by-side across the period at the end of this sentence and still have room for more. They are called particulate matter less than 2.5 millionths of a meter in diameter, or PM2.5 for short.

These particles avoid the efficient filters and traps of the respiratory system and get drawn deep into the lungs. Over time, they hasten the aging-related decline in lung function. Their effects are also felt far beyond the lungs.

Air quality forecast

The EPA publishes an Air Quality Index (AQI) daily at www.epa.gov/airnow.

Immediate and long-term effects
In the mid-1970s, Harvard researchers started a long-term study to look at the effects of air pollution on lung function and disability. After 15 years, their Six Cities Study showed a direct connection between death rates and the average daily level of fine particles in the air. It also revealed something unexpected — that many of the deaths were from cardiovascular disease.

A string of subsequent studies, including one covering more than 50 million people in the 20 largest U.S. cities, indicate that tiny particles, ozone, and other pollutants have both immediate and long-term effects on the heart and blood vessels. People with underlying heart disease or diabetes are most susceptible to these effects, as are the elderly and the poor.

Immediate effects. On days when air pollution levels are high, such as during a string of hot, hazy summer days, death rates are higher. There are more heart attacks and hospitalizations for heart disease, stroke, heart failure flare-ups, and lung trouble. A report in the June 2005 issue of Environmental Health Perspectives, by Harvard’s Douglas W. Dockery (a leader of the Six Cities Study) and colleagues, shows that implanted cardioverter/defibrillators detect more serious heart-rhythm disturbances, and fire more frequently, when air pollution levels are high.

Long-term effects. The Six Cities Study showed one important effect of chronically breathing polluted air: additional early deaths due to cardiovascular disease. In spring 2005, a group from the University of Southern California showed another — more atherosclerosis, the process that leads to cholesterol-clogged arteries. Among residents of the Los Angeles Basin, those living in areas with the highest average level of fine particulates had thicker carotid arteries (a sign of more atherosclerosis) than those living in less polluted areas.

What’s the connection?
How pollutants in the air influence the heart is still something of a mystery. They may pass through the lungs and act directly on the heart and blood vessels. They may add to the body’s pool of oxidants, substances that contribute to atherosclerosis and damage DNA. They may fan inflammation throughout the body. They may also stimulate nerves in the lungs that communicate with the central nervous system.

Whatever the mechanism, tiny particles and other air pollutants

  promote the formation of blood clots in your arteries, which can cause strokes and heart attacks

  add to inflammation, a key step in the development and progression of atherosclerosis

  increase the fragility of cholesterol-filled plaques embedded in the lining of arteries; when plaque ruptures, the blood clots that form to seal the break can cause a heart attack or stroke

  contribute to heart-rhythm abnormalities, including the deadly type known as ventricular fibrillation.

Clearing the air
Air pollution is a big, complex problem with national repercussions. It’s also an individual problem with personal ramifications.

If you have heart disease, diabetes, or lung problems, or are in poor health, consider checking the air quality before going outside, much as you might check the weather. Many newspapers now print air quality forecasts, like the one shown above, on the weather page. The Environmental Protection Agency maintains a Web site (www.epa.gov/airnow) that shows levels of ozone and particulates across the country, along with a health alert system and recommended changes in activity. Some states or regions even have air quality alert programs that automatically send you an e-mail message or fax when poor air quality is predicted in your area.

Moving to a place with cleaner air isn’t an option for most people. What we really need is cleaner air all around. That will take the talents and efforts of everyone from the U.S. Congress to state and local officials. And you.
The EPA estimates that merely meeting the National Ambient Air Quality Standards set in 1997 would save 23,000 lives a year. Creating and meeting stronger standards, especially for particulates, would be even better. A national push for fuel efficiency and greater use of wind and solar energy would further clear the air.

You can make a difference, too. Keep your car tuned up. The next time you buy a car, choose an energy-efficient model instead of a gas-guzzling Hummer or SUV. Better yet, walk more and drive less. The exercise will do you, and the air, a world of good.

Copyright 2006 Harvard Medical International