"We wondered, if someone has a specific variation in this ABO gene, are they more or less likely to experience a heart attack in times of higher pollution?" says clinical epidemiologist Benjamin Horne from the Intermountain Medical Center Heart Institute in Salt Lake City, Utah.
Horne's team analysed data from Intermountain Healthcare patients seen between 1993 and 2007, and identified a subset of patients that experienced an acute coronary syndrome (ACS) event corresponding with short-term exposure to high PM2.5 levels – a measure of concentration of fine, inhalable particles with a diameter of 2.5 micrometres and smaller.
When they cross-matched the data, they found that carriers of an ABO variant called rs687289 A allele had a marginally higher risk of heart trouble during high PM2.5 concentrations.
"The primary mutation we studied differentiates between O blood types and non-O, which includes positive and negative A, B, and AB blood types," says Horne.
"The one that's been found in genetic studies to be lower risk is O. The other three were higher risk."
That said, everybody's level of risk appears to rise when PM2.5 concentration rises above the threshold of 25 micrograms of fine particles per cubic metre of air – it's just that the risk goes up more for people with non-O blood types.
"Two years ago we published findings that showed once you go above that, each additional 10 micrograms of pollution per cubic metre of air provided substantially higher risks," says Horne.
"At levels higher than 25 micrograms per cubic metre of pollution, the increase in risk is linear, while below that level there's little if any difference in risk."
For each 10 additional micrograms of PM2.5 particles per cubic metre, risk for people with non-O blood types goes up by 25 percent, whereas for people with O blood it only goes up by 10 percent.
It's not the only time recently that blood types have been linked with these kind of cardiac problems.
A study presented in April analysed more than 1.3 million people and also found that people with non-O blood types stood a higher risk of cardiovascular events including heart attacks and stroke, although it did not establish what causal mechanisms were behind the pattern.
In reference to the latest research, the team says the new findings aren't anything to panic over, but are worth being aware of.
"In the information we provide to our patients about pollution, we try to stress that they can do something about it to reduce their risks," Horne says.
"Stay indoors out of pollution. Exercise indoors. And make sure they're compliant with taking their heart medication to reduce their risk."
The findings were presented this week at the American Heart Association's Scientific Sessions 2017 conference in Anaheim, California.
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