Researchers collected data on 23,179 hospital stroke admissions from 1997 to 2000 in Kaohsiung, Taiwan the island's second largest city and heavy industrial area. They compared air pollution levels on the dates of admissions with air pollution levels one week before and one week after admissions, said Chun-Yuh Yang, Ph.D., M.P.H., professor, director and dean at the Institute of Public Health, College of Health Sciences at the Kaohsiung Medical University.
The researchers found an association between exposure to increasing levels of two common pollutants and hospital admissions for stroke, particularly on warm days, i.e., 20 degrees Celsius or warmer (68 degrees or warmer Fahrenheit).
"Particulate matter (PM10) and nitrogen dioxide (NO2) seem to be the most important pollutants and the effects appear to be stronger on warm days," Yang said.
For each interquartile change 66.33 microgram per cubic meter change for PM10 and 7.08 parts per billion change for NO2 the risk of hospital admission for primary intracerebral hemorrhage (bursting of a defective brain vessel) increased by 54 percent.
The risk of hospital admission from ischemic stroke (resulting from a blood clot blocking blood flow to the brain) increased by 46 percent for PM10 per interquartile change and 55 percent for NO2 per interquartile change.
Studies have shown associations between air pollution and daily death rates for respiratory and heart disease. But findings related to pollution's effect on stroke have conflicted.
"This study provides new evidence that higher levels of ambient pollutants increase the risk of hospital admissions for stroke, especially on warm days," he said.