May 13 (HealthDay News) -- Exposure to coarse airborne-pollution particles, such as those found in windblown dust or stirred up by agricultural work and mechanical grinding, does not appear to be linked to hospital admissions, a new study finds.

Coarse particulate matter, or PM10-2.5 for short, is between 2.5 and 10 micrometers or microns (thousandths of a millimeter) in size -- much smaller than a pinhead.

To date, research into health risks posed by coarse particulate matter pollution has been mixed, according to background information in the article, printed in the May 14 issue of the Journal of the American Medical Association.

Exposure to fine particulate matter (PM2.5), which is smaller than 2.5 micrometers, has been studied far more extensively in the past decade and researchers have linked it to a higher risk of illness and death. Fine particulates, which are more likely to result from engine combustion, can reach the smaller airways and air sacs within the lungs.

In the study, researchers at Johns Hopkins Bloomberg School of Public Health, in Baltimore, analyzed data that included daily cardiovascular and respiratory disease admission rates at hospitals, temperature and dew-point temperature, and coarse- and fine-particulate concentrations from 108 U.S. counties from January 1999 through December 2005.

During that time, 3.7 million cardiovascular disease admissions and 1.4 million respiratory disease admissions occurred; however, this number was barely affected (by less than 1 percent) on days when coarse particulate concentrations were high and the amount of fine particulate was factored out, according to the findings.

"We did not find statistically significant associations between same day PM10-2.5 concentration and emergency hospital admissions for cardiovascular or respiratory diseases when we adjusted for PM2.5," the authors wrote.

The authors recommended that monitoring of coarse particulate matter for future studies continue and that the U.S. Environmental Protection Agency consider the findings the next time it updates its National Ambient Air Quality Standards.

SOURCE: JAMA, news release, May 13, 2008