Long-term exposure to air pollution, particularly particulate matter (PM) 2.5, has been linked with an increased risk of heart attack and other cardiovascular diseases, according to a new study.

In a diverse cohort of 3.7 million adults in California, the study published in Jama Network Open found that long-term PM 2.5 exposure was associated with an increased risk of incident acute myocardial infarction (AMI), ischemic heart disease mortality, and cardiovascular disease mortality.

These associations were more pronounced in low socioeconomic status communities. The results add to the growing evidence that long-term PM 2.5 exposure is associated with an increased risk of cardiovascular events and current regulatory standards of PM 2.5 are not sufficiently protective.

The retrospective cohort study included adults in the Kaiser Permanente Northern California integrated healthcare system from 2007 to 2016 and followed for up to 10 years. The participants had no prior stroke or acute myocardial infarction (AMI).

Fine particulate air pollution is recognised as a risk factor for cardiovascular events and mortality. However, several key gaps in knowledge remain.

First, a recent meta-analysis found much weaker evidence for the association of long-term PM2.5 with incident acute myocardial infarction (AMI) than with cardiovascular mortality outcomes.

Second, there is a gap in knowledge on susceptibility factors such as age, sex, race and ethnicity, and socioeconomic status (SES), where previous studies examining these factors have reported mixed and inconsistent results.

"Finally, controversy still remains as to whether the current US National Ambient Air Quality Standard of 12 Ig/m3 (micrograms per cubic metre of air) for annual mean exposures is sufficiently protective of adverse health effects," said the researchers.

The latest study concluded that long-term PM2.5 exposure at moderate concentrations was associated with increased risks of incident AMI, IHD mortality and CVD mortality.

The findings add to the evidence that the current regulatory standard is not sufficiently protective, said the researchers.