A new study of American cities showed that in recent decades, average life expectancy went up by nearly three years, of which 5 months can be
attributed to cleaner air.
The study was the work of researchers at Brigham Young University (BYU) and Harvard School of Public Health (HSPH) and is published in the 22 January issue of the New England Journal of Medicine.
Previous research has already shown that exposure to air pollution, as measured by the amount of fine particles in the air, is linked to higher rates of illnesses and deaths, suggesting that when air quality improves, these rates should go down, so the authors of this study decided to investigate the effect of changes in air pollution during the 1980s and 1990s on life expectancy.
For the study, the researchers brought together life expectancy, socioeconomic and demographic data for 51 US cities with matching data on air pollution for the two decades spanning the late 1970s to the early 2000s. They used statistical regression tools to search for significant links between pollution changes and life expectancy, while ruling out the effect of socioeconomics and demographics (eg population changes, income, migration and education), and cigarette smoking.
The researchers used the PM2.5 measure of air pollution that assesses levels of particles smaller than 2.5 microns in diameter (that is smaller than four hundredths of the width of human hair). This threshold was set by landmark studies on air pollution in the 1990s, which some of the authors in this study worked on. The threshold was also used by the US Environmental Protection Agency to set standards for air pollution in 1997.
The results showed that:
- A decrease of 10 micrograms per cubic meter in the concentration of fine particles was linked to with an estimated increase in mean life expectancy of more than 7 months (0.61 years plus or minus standard error of 0.20 y, p=0.004).
- This link was largely unaffected by ruling out potential confounders such as changes in socioeconomic, demographic, or smoking prevalence, and neither was it much affected by ruling out the fact the data came mostly from the larger counties in the 51 cities.
- In cities with the largest reduction in air pollution, the estimated increase in life expectancy was about 10 months.
- Drops in air pollution accounted for as much as 15 per cent of the overall rise in life expectancy in the 51 cities, which on average came to 2.72 years over the two decades studied.
"A reduction in exposure to ambient fine-particulate air pollution contributed to significant and measurable improvements in life expectancy in the United States."
Lead author C. Arden Pope III, an epidemiologist at BYU told the press that "such a significant increase in life expectancy attributable to reducing air pollution is remarkable," adding that America was getting a good return on the investment made in air quality improvement for not only was the cleaner air improving the environment but it was also improving public health.
Other studies suggest these improvements are most likely due to reductions in diseases that normally come with high air pollution, such as those that affect the heart, lungs and circulation.
Co-author Douglas Dockery, chair of the Department of Environmental Health at HSPH said:
"There is an important positive message here that the efforts to reduce particulate air pollution concentrations in the United States over the past 20 years have led to substantial and measurable improvements in life expectancy."
His colleague and co-author Majid Ezzati, associate professor of international health at HSPH, added:
"Life expectancy is the single most comprehensive summary of how people's longevity is affected by factors like air pollution that cause early death."
"We were able to use routine mortality statistics to track longevity in all cities over a long period of time and analyze how it has been influenced by changes in air pollution," said Ezzati.
The study was sponsored by the US Centers for Disease Control and Prevention, the Association of Schools of Public Health, the Environmental Protection Agency, the National Institute of Environmental Health Sciences, and the Mary Lou Fulton Professorship at BYU.
"Fine-Particulate Air Pollution and Life Expectancy in the United States."
Pope, C. Arden, III, Ezzati, Majid, Dockery, Douglas W.
N Engl J Med Volume 360, No 4, pp 376-386, 22 Jan 2009.
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Sources: Brigham Young University , journal abstract.
Written by: Catharine Paddock, PhD