The study looked at hospital discharges for people with these four types of diseases living in 34 cities between 1985 and 1999. The researchers compared this information with 12-month averages of PM10, a type of particulate matter air pollution that includes particles with a diameter of 10 micrometers or less than 0.0004 inches or one-seventh the width of a human hair.
The study found that for an increase of 10 micrograms/per cubic meter of PM10 over two years, the risk of dying was increased by:
- 32% for people with diabetes
- 28% for people with COPD
- 27% in people with congestive heart failure
- 22% for people with inflammatory disease such as rheumatoid arthritis or lupus
"The study significantly strengthens evidence that breathing in particulate matter is associated with dying sooner," said researcher Joel Schwartz, Ph.D., Professor of Environmental Epidemiology at the Harvard School of Public Health in Boston.
"While previous studies have found that long-term exposure to air pollution is associated with increased risk of death, we looked at risk of death in the first three years after patients were discharged from the hospital, and saw that the risk increased in the first couple of years. That means if we can lower air pollution levels, people will start living longer right away--we don't have to wait many years to see health improvements. That wasn't clear from previous air pollution studies."
Technology that can reduce particulate matter levels already exists, Dr. Schwartz noted. "For instance, we know how to put scrubbers on coal-burning power plants, which are a major source of particulate matter. There is no safe level of particulate air pollution, so we need to get the levels as low as reasonably possible."
While previous studies have linked exposure to PM10 to harmful effects on breathing and respiratory systems, damage to lung tissue, cancer, and premature death, this is the first study to follow people with specific diseases to determine their risk of death in response to particle exposure, Dr. Schwartz said.
He noted an important difference between this new study and past air pollution studies. "Past studies have compared average air pollution conditions in one city to other cities, and you need to worry about potential confounders, or other factors that could affect the differences between the cities," he said. "In this study, we looked at air pollution and deaths within each city--we didn't compare across cities, so we didn't need to worry about confounding factors."
The study helps validate the findings of previous studies that have shown that long-term exposure to air pollution is associated with shortened survival in the general population, said Dr. Schwartz, a co-author of the Six Cities Study, which evaluated the effects of pollution on adults in the 1970s and 1980s. The results of that study found a strong, positive correlation between levels of air pollution and mortality. The study led to a revision of existing air quality standards by the U.S. Environmental Protection Agency. An eight-year follow up study found an association between people living longer and cities reducing the amount of fine particulate matter in their air. That study was published in the March 15, 2006 issue of the American Thoracic Society journal, The American Journal of Respiratory and Critical Care Medicine.