Investigators who extended the Harvard Six Cities fine particulate air pollution study by eight years found that reduced levels of tiny particle pollution during this period lowered mortality risk for participants.
The results appear in the second issue for March 2006 of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
The findings of the original Harvard Six Cities study (1979 to 1990) revealed an association between levels of fine particulate matter pollution and mortality risk. The new study, which was conducted from 1990 to 1998, reports on this later period of reduced air pollution concentration.
Francine Laden, Sc.D., of Channing Laboratory in Boston, Massachusetts, and three associates found that the largest drops in adjusted mortality rates were in cities with the greatest reduction in fine particulate air pollution (PM2.5). The investigators' findings remained valid even after setting controls for the general increase in adult life expectancy that occurred in the U.S. during both study periods (1979 to 1989 and 1990 to 1998).
"This reduction was observed specifically for deaths due to cardiovascular and respiratory disease and not from lung cancer, a disease with a longer latency period and less reversibility," said Dr. Laden.
The study population consisted of 8,096 white participants residing in Watertown, Massachusetts; Kingston and Harriman, Tennessee; St. Louis, Missouri; Steubenville, Ohio; Portage, Wyocena, and Pardeeville, Wisconsin; and Topeka, Kansas. The average age of participants at the start of the original study was 50, with women comprising 55 percent of the cohort.
"Current smoking on enrollment ranged from 33 percent in Topeka and 40 percent in Watertown, and former smoking ranged from 21 percent in Harriman to 25 percent in both Topeka and Watertown," said Dr. Laden.
The annual mean concentration of PM2.5 (fine particulate matter) declined during the eight-year study period by 7 micrograms per cubic meter of air per decade in Steubenville, 5 micrograms in St. Louis, 3 micrograms in Watertown, 2 micrograms in Harriman, 1 microgram in Portage and less than a microgram in Topeka.
The improved mortality relative risk due to decreased PM2.5 during the second study period, as compared to the first, was 0.73.
In an editorial on the article in the same issue of the journal, Bert Brunekreef, Ph.D., of the Institute for Risk Assessment Science at the Universiteit Utrecht and the University Medical Center in Utrecht, The Netherlands, wrote: