"The results suggest that repeated periods of short-term (e.g., several hours) exposure to high particulate matter levels, such that may occur during rush hour traffic, is potentially capable of promoting ... atherosclerosis," writes researcher Qinghua Sun, MD, PhD, with Mount Sinai School of Medicine in New York.
Eating a high-fat diet -- plus breathing rush-hour pollution -- produces an even more dramatic buildup of artery-clogging fat, especially in people with heart disease, Sun notes in his study, which appears in this week's edition of The Journal of the American Medical Association.
Studies have pointed to a link between air pollution and heart disease, they write. However, it's been difficult for researchers to understand just how breathing particulate matter damages blood vessels, he writes.
His findings add to a growing body of data showing that particulate matter from air pollution causes damaging inflammation leading to plaque buildup in blood vessels. It is possible that when particulates enter the lungs, they trigger an inflammatory response in lung cells, which then triggers inflammation in blood vessel walls -- all of which leads to plaque buildup and atherosclerosis, Sun explains.
Air pollution particles can also affect blood vessel health by impairing its ability to dilate. Normal blood vessels dilate in response to blood flow; impaired function is an early sign of atherosclerosis.
Sun's study involved laboratory mice that breathed New York City-style polluted air, complete with power plant emissions, vehicle exhaust, dust, soot, and smoke. The size of particles in the pollution was the size linked most strongly with heart disease. The EPA has regulated this particle size since 1997, Sun notes.
The 28 mice were all genetically prone to developing heart disease. They were divided into two groups -- one eating a normal diet, the other eating a high-fat diet. During the six-month study, half the mice in each feeding group breathed either polluted or filtered air.
Researchers imaged and examined the largest artery of the body -- the aorta -- in all the mice. They found:
- Those eating a normal diet and breathing polluted air had 19% of the examined blood vessels clogged with plaque; those breathing filtered air had 13%.
- Among mice eating a high-fat diet -- and breathing polluted air -- 42% of the arteries examined were clogged. Mice that ate a high-fat diet but got filtered air had 26%.
- Pollution-breathing mice had higher cholesterol levels, whether they ate a normal or high-fat diet.
- Mice exposed to pollutants were prone to developing abnormal blood vessel dilation, yet those eating the high-fat diet (whatever air they breathed) had more dramatic impairment, compared with the normal-diet group.
Researchers examined other measures of artery inflammation. They found increased levels of macrophages, immune cells that are an important ingredient in inflammation and plaque deposit development, writes Sun.
A study of rabbits showed a similar pattern linking pollution with artery-clogging plaque. However, Sun's study has an important difference; it utilizes pollution levels at low-level concentrations that people living in urban areas (like New York City) are exposed to every day.
Thus, his findings have implications for the long-term impact of particulate exposure on urban populations, he writes.