By Deborah Blum, November 15, 2013
Bit by bit over the past few decades, scientists have been building a
new understanding of the ways that air pollution threatens human
health. Much of their attention has been focused on lung diseases,
including cancers. With good reason, it turns out: just last month, the
World Health Organization declared air pollution to be one of the
planet’s most dangerous environmental carcinogens.
But cardiovascular disease is much more common than cancer. Sadly,
there is now a pile of evidence, sometimes startling, that air pollution
also plays a role in heart attacks and strokes. The new studies suggest
that air pollution not only worsens cardiovascular disease — but can also cause it.
“We’ve known for about 20 years that we see increased risk of heart
attack and stroke in association with increased levels of air
pollution,” said Sara Adar, a professor of epidemiology at the
University of Michigan. The most recent data show that “air pollution
does more than just make you worse.”
Scientists like Dr. Adar have been studying fine particulates
adrift in the cloud of unfriendly gases shrouding many of our
communities. Measuring 2.5 micrometers (or microns) or less, these bits
of material are so tiny that it would take about 30 of them to equal the
diameter of a human hair. A series of studies has found that they
penetrate deep into the lungs, embedding in tissue and setting off a
cascade of inflammatory effects. Researchers believe the inflammation
also spreads into the circulatory system, altering the way blood vessels
Although air pollution is a long-recognized and regulated health
hazard, only gradually have researchers come to appreciate the threat of
particulates. In 1989, C. Arden Pope III, a professor of economics at
Brigham Young University, published a paper based on the temporary
shutdown of a nearby steel mill, showing a linear relationship between emissions and hospitalizations. He traced the illnesses to particulates in the air.
Dr. Pope originally had focused on air pollution’s effects on the
lungs, but over the years he kept turning up increases in cardiovascular
disease. “By 2002, I’d given up on the idea that this was just some
anomaly in the study design,” he recalled in an interview. Eventually he
identified the culprit: fine particles, far smaller than those tracked
in his original steel mill study. “The deeper you dive into the data,
the more clearly you see the effect on cardiovascular disease,” Dr. Pope
Dr. Adar and her colleagues have been tracking the damage at the microscopic level in the Multi-Ethnic Study of Atherosclerosis and Air Pollution
(MESA Air), which has followed more than 5,000 people in six states for
more than a decade. It is funded primarily by the National Institutes
of Health and the Environmental Protection Agency.
Researchers working with the project have contributed to an
increasingly precise understanding of risks associated with fine
particles that float in polluted air. Dr. Adar and her colleagues have
shown, for instance, that increased exposure to pollutants, after other
factors are factored out, can be directly linked to narrowing of blood vessels and to a steady thickening of artery walls.
Their most recent study, published this year in PLoS Medicine,
described a near-linear relationship: as air pollution levels dropped, the thickening slowed. When exposure to air pollutants increased, signs of damage increased.
The MESA Air study also has reinforced a sense that vehicle exhaust
may be unusually harmful. Researchers in the United States and many
other countries have linked traffic pollution to heart rate variability
in a range of people – from vehicle drivers to bicyclists traveling
congested roadways. A study published this year in Environmental Health
found evidence of “acute changes” in heartbeats in people, aged 22 to
56, driving in Mexico City traffic. Another recent study, of bicyclists in Ottawa, found that their heart rhythms appeared to be altered for hours after they had returned home in ways unrelated to exertion.
“There’s increasing evidence that there’s something about
traffic-related pollution in particular,” said Dr. Joel D. Kaufman, an
epidemiologist at the University of Washington in Seattle.
Vehicle emissions are thought to include an unusually high proportion
of very small, or ultrafine, particles, allowing them to penetrate
deeper into the body. Researchers say there is also some evidence that
the shape of these particles gives them an unusually high surface area,
which permits other contaminants to stick onto them. As a result, they
may actually concentrate toxic compounds in polluted air.
“The evidence is pretty overwhelming that fine particles do harm,”
said Dr. Russell V. Luepker, a cardiologist and epidemiologist at the
University of Minnesota School of Public Health, a co-author of two
scientific reports on air pollution for the American Heart Association.
But, he added, health choices — such as poor diet, smoking and lack
of exercise — and conditions such as hypertension still pose greater
risks. “If we got rid of air pollution, heart disease would not
disappear,” Dr. Luepker said.
Researchers studying the healt
h effects of air pollution are starting
to look at ways that their findings can be used for greater protection.
Dr. Adar and her colleagues are looking for ways to better identify and
control the most dangerous vehicle emissions, while other scientists
are pondering everything from improved air purifiers to
particle-absorbing barriers. But one of the most effective responses is
Several decades of clean air regulations in the United States have
had lifesaving effects. A study published this year in the Journal of
the American Medical Association estimated that there has been a 35 percent drop in deaths and disabilities related to air pollution, including cardiovascular diseases, in the United States since 1990.
“Our public policy efforts to reduce air pollution are one of the
most effective medical interventions in the last 20 to 30 years,” Dr.