The tiniest bits of air pollution from your vehicle’s exhaust may be the most dangerous to your heart’s health, suggests a new U.S. study.

Particles that are about one-thousandth the size of a human hair, cause plaque build-up in the arteries, according to a University of California, Los Angeles-led study. This condition, called atherosclerosis, can lead to heart attack and stroke.

These particles also contribute to hardening of the arteries by shutting down the protective qualities of so-called “good” high-density lipoprotein (HDL) cholesterol, according to the study, which appears in the Jan. 17 online edition of Circulation Research.

Over five weeks, researchers exposed mice with high cholesterol to larger fine pollution particles (2.5 micrometers in size) or ultrafine particles (less than 0.18 micrometers), then compared them to mice exposed to filtered air. The mice exposed to ultrafine particles had 25 percent more arterial plaque development than the mice exposed to fine particles and 55 percent more than mice that breathed filtered air.

“This suggests that ultrafine particles are the most toxic air pollutants in promoting events leading to cardiovascular disease,” study author Dr. Jesus Araujo, an assistant professor of medicine and director of environmental cardiology at UCLA’s David Geffen School of Medicine, said in a prepared statement.

While the U.S. Environmental Protection Agency regulates fine pollution particles, it doesn’t monitor ultrafine — or nano-sized — particles, according to background information in a news release about the study.

“We hope our findings offer insight into the impact of nano-sized air pollutant particles and help explore ways for stricter air quality regulatory guidelines,” principal investigator Dr. Andre Nel, UCLA’s chief of nanomedicine, said in a prepared statement.

(Source: NHIC)