Air Pollution Is Dangerous, but Deadly?
Long-Term Ozone Exposure Boosts Risk for Lung-Related Death, Study Shows
By
Bill Hendrick
WebMD Health News
Reviewed By
Louise Chang, MD
March 11, 2009 -- Long-term exposure to ground-level ozone significantly
increases the risk of death from respiratory problems, a new study shows.
A team of scientists says the risk of dying from respiratory problems is
more than 30% greater in metropolitan areas with the highest ozone
concentrations than areas where ozone levels were the lowest.
Ground-level ozone, along with particulate matter, is a major component of
smog. Ozone is a naturally occurring gas most prevalent high in the atmosphere,
where it protects against harmful ultraviolet rays of the sun. However, ozone
at ground level is produced when exhaust from cars, power plants, and other
sources reacts chemically in sunlight. According to the Environmental
Protection Agency, ground-level ozone can irritate breathing, decrease lung
function, inflame airways, and worsen lung conditions such as asthma and
emphysema.
Previous studies have shown that long-term exposure to fine particulate
matter -- tiny particles of dust and soot -- are a major risk factor for death
from heart and lung disease.
But until now, it was unclear whether ozone was linked to a higher risk of
death from lung disease itself, Michael Jerrett, PhD, tells WebMD. Jerrett is
an associate professor of environmental health at the University of
California-Berkeley and lead author of the study.
Now that's no longer in question, he says.
"This is the first study to show that ozone, long considered a secondary
pollutant, is a key cause of death," he says. "This is the first time we've
been able to connect chronic exposure to ozone with the risk of death."
Ozone vs. Fine Particulate Pollution
The study, published in the March 12 issue of The New England Journal of
Medicine, followed 450,000 people from 1982 to 2000 and covered 96
metropolitan regions. Over the 18-year study period, 118,777 people died.
"The study presents evidence for the first time that long-term exposure to
ozone and fine-particulate pollution have separate, independent effects on
mortality, and that they seem to impact different parts of the body," Jerrett
tells WebMD.
The study also makes clear that controlling ozone would not only reduce
deaths, but mitigate global warming, Jerrett says.
George D. Thurston, ScD, a professor of environmental medicine at New York
University School of Medicine and a study co-author, says ozone tends to form
in higher concentrations in suburbs and rural areas downwind of cities.
That's due in part to commuting patterns, Jerrett says. It's hard to keep
counts down when governments at all levels can't control sprawl and
"one-person-per-car-commuting," he says.
Cities With the Highest Ozone Levels
The risk of dying from respiratory causes rises up to 4% for every 10
parts-per-billion increase in exposure to ozone, the study says. Jerrett
tells WebMD that over the 18-year study period, Riverside, Calif., had the
highest daily average maximum concentration at 104 parts per billion, which
"corresponded to a 50% increased risk of dying from lung disease compared to no
exposure" to ozone.
He adds that in general, cities in the Northeast had lower ozone than
California. New York had a 25% increased risk of lung-related death and
Washington, D.C., came in at 27%, compared to 43% in Los Angeles.
The lowest ozone concentrations were recorded in San Francisco.
Charlotte-Gastonia, N.C., Chattanooga, Tenn., Raleigh, N.C., and Richmond,
Va., were among the most ozone-rich areas in the South.
Limiting Exposure to Ozone Air Pollution
A clear message to the public, Jerrett says, is that exercise during the
sunniest time of the day should be avoided by people who live in warm climates.
He also says it's smart to keep windows closed when ozone levels are highest,
and it's just not good to spend more time outside than indoors when levels of
the gas are high.
Cherry Wongtrakool, MD, a pulmonologist and professor at the Emory
University School of Medicine in Atlanta, says "you need particulates to have
ozone, which depends on sunlight."
Plus, ozone is more seasonal, occurring at highest levels from spring to
fall. She recommends commuting less and exercising, but not around busy streets
in warm weather.
"Thirty percent is a very alarming number," she says.
As for governments, Jerrett says, they should take steps to reduce traffic
congestion, perhaps by offering financial incentives to carpoolers, increasing
high-occupancy lanes, encouraging the use of hybrid cars and maybe even by
discouraging driving with higher gas taxes.
Jerrett says studies have shown that high ozone levels can cause problems
quickly, and that reports on ozone levels, which can often be found in
newspapers or on the Internet, should be consulted by people considering
outdoor exercise.
Janice E. Nolen of the American Lung Association says the study suggests
that "even low-ozone days kill people early" and that "controls have to be put
on cars and power plants" to deal with this.
Ozone, she says, "is a huge problem around the country. Your lungs are
getting repeatedly assaulted."
But the problem isn't insurmountable, Jerrett says, noting a recent New
England Journal of Medicine study reporting that the average life expectancy in 51 U.S. cities had increased nearly three years
between 1980 and 2000, with up to five months of that a result of decreased air
pollution.
SOURCES: News release, University of California, Berkeley. News release, NYU Langone Medical Center, of New York University. WebMD Health News: "Life Expectancy Up, Thanks to Cleaner Air." EPA: "Ozone and Your Health." Jerrett, M. New England Journal of Medicine, 2009; vol 360: pp
1085-1095. Cherry Wongtrakool, professor of medicine, Emory University School of
Medicine. Janice E. Nolen, American Lung Association, Washington, D.C.
©2009 WebMD, LLC. All Rights Reserved.
Asthma RSS