Researchers at the University of California at Los Angles, the University of Southern California, the University of California at Irvine and Michigan State University said that their study demonstrated the ability of nano-sized air pollutants to promote atherosclerosis in an animal model.
Nanoparticles are the size of a virus or molecule -- about one-thousandth the size of a human hair. The government doesn't monitor particles in the nano or ultrafine range.
Study leader Dr. Andre Nel of UCLA said the pollutant particles may promote hardening of the arteries by inactivating the protective qualities of high density lipoprotein, or HDL, known as "good" cholesterol.
"It appears that the smallest air pollutant particles, which are the most abundant in an urban environment, are the most toxic," first author Dr. Jesus Araujo of the David Geffen School of Medicine at UCLA said in a statement.
The findings are published in the journal Circulation Research.