High Blood Pressure? Traffic Exhaust May Be to Blame

Breathing unfiltered air while driving on busy roads during rush hour may increase blood pressure as much as a high-sodium diet.

An average American spends 293 hours driving a year, exposing themselves to traffic pollution that has been associated with an increased risk of cardiovascular disease, asthma, and other conditions.

A new study from researchers at the University of Washington gives new insights into how traffic exhaust harms our health.


Published in the Annals of Internal Medicine, the study found that unfiltered air from rush-hour traffic significantly increased participants' blood pressure while in the car and up to 24 hours later.

Air filters make the difference

The researchers took 16 healthy participants aged 22 to 45 who had normal blood pressurefor three rides through rush-hour Seattle traffic while monitoring their blood pressure.

On two of the drives, unfiltered road air was allowed to enter the car. On the third, the vehicle was equipped with high-quality HEPA filters blocking out 86% of particulate pollution. Participants did not know whether they were on a clean air drive or a roadway air drive.

Breathing unfiltered air from the traffic raised blood pressure by more than 4.50 mm Hg compared to driving in a car with filtered air. The increase was sudden and peaked about an hour into the drive. At 24 hours, blood pressure remained slightly elevated.

Researchers say increases in blood pressure due to traffic exhaust are comparable to those caused by a high-sodium diet. Although modest, such increases on a population level are linked to significantly higher rates of cardiovascular disease.

"There is a growing understanding that air pollution contributes to heart problems. The idea that roadway air pollution at relatively low levels can affect blood pressure this much is an important piece of the puzzle we're trying to solve," said Joel Kaufman, a UW physician and professor of environmental and occupational health sciences who led the study.

However, the findings should be interpreted cautiously due to the small number of participants.


The findings also raise questions about ultrafine particles, little-understood and unregulated pollutants less than 100 nanometers in diameter, found at high traffic exhaust levels.

The researchers note that because ultrafine particles were most effectively filtered in the experiment, they may play an important role in raising blood pressure. However, further studies are necessary to prove the causal relationship.

Children are especially vulnerable

Traffic-associated pollution is a serious health concern for more than 45 million Americans living, working, or attending school within 300 feet of a major road, airport, or railroad, according to the Environmental Protection Agency (EPA).

Traffic pollution is especially dangerous to children because it can impair their lung development and cause asthma and childhood leukemia. Pregnant women exposed to traffic exhaust are at an increased risk of giving preterm birth or low-birthweight infants.

The new study linking traffic exhaust to increased blood pressure adds to the puzzle of how pollution harms our health.


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