Chicago, IL - Short-term exposure to fine-particle air pollution at concentrations usually within the range allowed by proposed US federal regulations can increase the risk of hospitalization for cardiovascular and respiratory disease, according to an analysis of Medicare, weather, and smog-level data from across the US [1].

Dr Francesca Dominici (Johns Hopkins University, Baltimore MD) and associates saw the higher health risks in association with day-by-day elevations in levels of airborne particulate matter <2.5 µm in diameter (PM-2.5), which the US Environmental Protection Agency (EPA) has proposed to restrict to concentrations of <35 µg/m³ as the 24-hour air-quality standard [2]. But even that upper limit may not go far enough, according to the new analysis. Daily PM-2.5 levels exceeded the proposed standard "only about 3% of the time," she said, yet the increased health hazard was evident even at the lower concentrations. "This is going to be a huge piece of evidence saying that PM-2.5 is harmful to human health at levels that most of the time are below the proposed standard."

The emphasis of research should shift toward the difficult issue of identifying those characteristics of particles that determine their toxicity.

The study, published in the March 8, 2006 issue of the Journal of the American Medical Association, adds to limited nationwide data on the health risks of 24-hour exposure to PM-2.5 in smog, Dominici told heartwire. There is more such information for individual US cities, and current EPA standards for daily PM-2.5 levels are set city by city. The agency, which has been regulating 24-hour concentrations of smog particles up to 10 µm in diameter, is accepting comments on its proposed daily PM-2.5 standard until April 17, 2006.

"Our findings indicate an ongoing threat to the health of the elderly population from airborne particles and provide a rationale for setting a PM-2.5 national ambient-air-quality standard that is as protective of their health as possible," the authors write.

The group gathered a vast set of 1999-2002 data from a range of sources that encompassed daily admission rates, diagnoses, and demographics from 11.5 million Medicare patients residing in 204 urban regions; nationwide particulate and ozone air-pollution readings from the EPA; and temperature and other environmental measures from the National Climatic Data Center. They made same-day comparisons of PM-2.5 level increases with admissions for a range of CV, cerebrovascular, and respiratory disorders. For ischemic heart disease and respiratory infections only, increased concentrations were compared with admissions two days later. After the researchers controlled for potential confounders that could vary from day to day as well as geographically, the results turned out to be largely consistent across the entire US, according to the report.

The HF-admission rate rose 1.28% for every 10-µg/m³ increase in PM-2.5, the group found. Corresponding increases for cerebrovascular disease, peripheral vascular disease, and chronic obstructive pulmonary disease (COPD) were 0.81%, 0.86%, and 0.91%, respectively. The group calculated hypothetical reductions in admission rates associated with each concentration decrease of the same magnitude.

The effects were sometimes more pronounced among persons 75 years and older. The rate for HF rose 1.36% for each 10-µg/m³ jump; their increase was 1.47% for COPD and 0.92% for respiratory infection.

"With clear and continuing indication that inhaled particles affect public health adversely, the emphasis of research should shift toward the difficult issue of identifying those characteristics of particles that determine their toxicity," the authors write.