SUNDAY, Feb. 17 (HealthDay News) -- Levels of ozone and of air pollution are directly linked to heart attacks, according to a new study from Houston.

For both ozone and airborne fine particulate matter (tiny solid and liquid pollutants such as those emitted by cars and factories), peak exposure was found to increase the risk for heart attack nearly 5 percent. Men, blacks and people older than 65 were at greatest risk, the investigators found.

These findings should prompt health officials to continue their efforts to reduce air pollution and provide the public with early warnings of high ozone levels, the study authors suggested.

"The bottom-line goal is to save lives," researcher Katherine Ensor, a professor and chair of the department of statistics at Rice University, said in a university news release. "We'd like to contribute to a refined warning system for at-risk individuals. Blanket warnings about air quality may not be good enough. At the same time, we want to enhance our understanding of the health cost of pollution -- and celebrate its continuing reduction."

In conducting the study, Ensor and colleagues examined eight years of data on air quality in Houston. They also reviewed information compiled by Houston Emergency Medical Services on more than 11,000 heart attacks that occurred outside of the city's hospitals. More than 90 percent of cases were fatal, and 55 percent occurred during the heat of summer.

Heart attacks were linked to exposure to both ozone and particulate matter smaller than 2.5 micrograms in the air. An average increase in fine particulate matter of 6 micrograms per day over the course of two days increased the risk for heart attack by 4.6 percent. People with pre-existing health problems would be at particular risk, the researchers noted.

Similarly, an ozone level increase of 20 parts per billion (ppb) in one to three hours increased the risk for heart attack up to 4.4 percent. However, nitrogen dioxide, sulfur dioxide and carbon monoxide levels did not affect the number of heart attacks, the researchers said.

Study co-author David Persse, EMS physician director for the Houston Fire Department, said that EMS workers have long believed that certain types of air pollution, including ozone, have serious harmful effects on people's hearts and lungs. "But this mathematically and scientifically validates what we know," he said in the news release.

The American Lung Association ranked Houston eighth in the United States for high-ozone days. The city is taking steps to reduce fatalities from heart attacks, such as increasing education on bystander CPR (cardiopulmonary resuscitation) in at-risk communities.

The best way to prevent the harmful effects of exposure to air pollution, however, is to improve air quality, according to Houston's Health and Human Services Department.

Rice University environmental engineer Daniel Cohan said that environmental strategies that reduce ozone year-round may be needed.

The researchers noted their findings could have important implications as states plan to meet national ozone standards. Although standards are now set at 75 ppb, the U.S. Environmental Protection Agency is considering tightening them to between 60 ppb and 70 ppb.

A 2012 study from Rice determined that the EPA's particulate standard of 35 micrograms per cubic meter does not go far enough to protect people's health.

The findings were scheduled for Sunday presentation at a meeting of the American Association for the Advancement of Science, in Boston. The study will also be published in the journal Circulation.

More information

Visit the U.S. National Institute of Environmental Health Sciences to learn more about ozone.