Air pollution tied to higher heart attack risk

NEW YORK: Breathing in dirty air may be linked to a higher chance of suffering a heart attack in the next few days, suggests a fresh look at past studies undertaken by French researchers.

While it's well established that people who spend years living in polluted cities or near major highways are at increased risk of heart problems, the new findings suggest even short-term exposure to pollution can be harmful.

"If you put together the evidence, clearly day-to-day changes in particle concentration do make a very small but significant difference in terms of increasing susceptibility for cardiovascular events" such as heart attacks, said Dr. Sanjay Rajagopalan, who studies pollution and cardiovascular health at The Ohio State University in Columbus.

"This seems to be particularly so for individuals with pre-existing heart disease," Rajagopalan, who wasn't involved in the new study, told Reuters Health.

Researchers led by Dr. Hazrije Mustafic from the Paris Cardiovascular Research Center found 34 studies that compared the risk of suffering a heart attack at various levels of industrial and traffic-related air pollutants including carbon monoxide, nitrogen dioxide and very small soot-like particles.

Those reports included anywhere from about 400 to more than 300,000 people, with heart attacks confirmed in hospital records and disease and death registries.

The combined findings showed that heart attacks were slightly more common at high levels of every main pollutant except ozone, Mustafic's team reported in the Journal of the American Medical Association.

The differences in heart risks were small. For most of the pollutants, an increase in concentration of 10 micrograms per cubic meter of air -- the typical standard used to assess harm, and barely noticeable to a person breathing the air -- was associated with a one to three percent increase in the chance of having a heart attack in the next week.

"Even if the relative risks are low compared with traditional risk factors such as smoking status or hypertension or diabetes, in fact everybody is exposed to air pollution in industrialized countries," Mustafic told Reuters Health -- so even small effects can add up.

She said that when people inhale polluted air, small particles can reach the tiny sacs in the lungs and be carried in the bloodstream to the heart.

Pollutants may also affect blood vessels' ability to expand and contract in order to keep blood pressure constant.

Researchers have blamed that effect for increasing evidence that high-pollution days are also tied to a person's risk of suffering a stroke, including findings from a study published Monday in the Archives of Internal Medicine. Another report in the same journal linked long-term exposure to air pollution with faster cognitive decline in older women (see Reuters Health story of February 13, 2012).

Mustafic said that air pollutants are associated with harmful health effects even at levels that are considered safe by the World Health Organization and other monitoring groups. That might mean it's time to lower some of the maximum allowable levels, she said.

"Clearly, air pollution at least in North America and Europe has remarkably improved in the last few decades," Rajagopalan added. But, "the epidemiology continues to support an association with even (current) levels and an increased risk of cardiovascular disease."

He said that people who should be concerned are those who already have heart disease, and possibly those who are at higher risk of a heart attack because of diabetes or obesity.

"If you're really at risk, it might be reasonable to avoid areas of high pollution (and) avoid commuting during those times or spending time in rush-hour traffic," Rajagopalan said. "Minimize exposure as much as you can."