Day-to-day spikes in air pollution seem to be followed by an uptick in hospital admissions for heart attacks, a new study in Italy finds.
The findings, reported in the American Journal of Epidemiology, add to evidence that high-pollution days may trigger heart attacks in some people.
And, like other studies, the new one suggests that the elderly and people with existing heart or lung disease are most vulnerable.
Already, the American Heart Association (AHA) recommends that people with heart disease and others at risk -- including the elderly and people with diabetes or high blood pressure — try to steer clear of congested roadways and spend less time outside on days when air quality is poorer.
The evidence of harm is strongest against pollutants known as fine particulate matter.
Fine particulate matter is released into the air when wood or fossil fuels are burned, so car exhaust, home heating and industrial sources like power plants all contribute.
The particles are small enough that they can be inhaled deeply into the lungs, and researchers suspect they may trigger heart attacks in vulnerable people by causing inflammation in the blood vessels and irritating the nerves of the lungs.
For the new study, researchers led by Dr. Alessandro Barchielli, of the Regional Health Service of Tuscany, looked at data on 11,450 hospitalizations for heart attack between 2002 and 2005.
They used local air-quality monitors to see how those hospitalizations correlated with changes in air pollution levels.
Overall, the study found that for each fine-particle increase of 10 micrograms per cubic meter of air, heart attack hospitalizations inched up 0.01 percent over the next two days.
There was a similar pattern when the researchers looked at two other traffic pollutants: carbon monoxide and nitrogen dioxide.
The link between pollution spikes and heart attack was strongest among people age 75 or older, and for those with the lung diseases emphysema or chronic bronchitis, and people with high blood pressure.
The findings alone do not prove that air pollution, itself, triggers heart attacks.
But they do add to other studies that have found a similar association, according to Barchielli's team.
They are also in line with what the AHA and other groups recommend for people vulnerable to heart problems: pay attention to air quality and, whenever possible, limit time outdoors on high-pollution days.
In the U.S., where heart attacks kill 425,000 people yearly, local news outlets generally provide daily air-quality indices; they are also available on the government website AIRNow.