Breathing in dirty air may be linked to a higher chance of suffering a heart attack a few days afterward, according to a French analysis of past studies.
Researchers led by Hazrije Mustafic from the Paris Cardiovascular Research Center found that heart attacks were slightly more common at high levels of every main pollutant except ozone, the group reported in the Journal of the American Medical Association.
They looked at 34 studies comparing the risk of suffering a heart attack, or myocardial infarction, at various levels of inhaling industrial and traffic-related air pollutants including carbon monoxide, nitrogen dioxide and very small soot-like particles.
The reports included anywhere from about 400 to more than 300,000 people, with heart attacks that were confirmed in hospital records and disease and death registries.
“All the main air pollutants, with the exception of ozone, were significantly associated with a near-term increase in myocardial infarction risk,” they wrote.
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.
When people inhale polluted air, small particles can reach the tiny sacs in the lungs and be carried in the bloodstream to the heart, she said.
Pollutants may also affect blood vessels' ability to expand and contract in order to keep blood pressure constant – an effect that researchers blame for increasing evidence that high-pollution days are also tied to a person's risk of suffering a stroke.
“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,” said 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,” he told Reuters Health, adding that at-risk people should minimize exposure to pollutants as much as possible.