Commuters beware. Travelling on a busy road might not only make you late for work but also risk your health because of the air pollution. A new study by researchers from the University of Washington found that polluted air from rush-hour traffic significantly increased passengers’ blood pressure, both while in the car and up to one day later.

Exhaust pipes can emit many air pollutants. The combustion of gasoline and diesel fuel results in the release of particulate matter, nitrogen oxides, carbon monoxide, and volatile organic compounds (VOCs), along with CO2, into the atmosphere. VOCs can undergo reactions with nitrogen oxides, leading to the formation of ozone pollution.

Air pollution from vehicles can affect health in many ways. For example, nitrogen oxides worsen asthma and particulate matter can lead to lung cancer. In 2010, a review estimated that between 30% and 45% of the people in North American cities live or work near enough to a busy road to experience significant levels of pollution.

Joel Kaufman, a physician and environmental researcher at the University of Washington, had shown in a 2008 study that exposure to exhaust fumes increased blood pressure in a controlled environment. Now, he took things to the next level, working on a new road traffic study to test that previous finding in a real-world setting.

“The body has a complex set of systems to try to keep blood pressure to your brain the same all the time. It’s a very complex, tightly regulated system, and it appears that somewhere, in one of those mechanisms, traffic-related air pollution interferes with blood pressure,” Kaufman, a professor of environmental health, said in a news release.

Health risks

In the study, Kaufman and his team drove healthy participants between the ages of 22 and 45 through rush-hour traffic in Seattle, while monitoring their blood pressure. On two of the drives, the researchers allowed unfiltered road air to enter the car, mirroring how many people drive. On the third, the car was equipped with high-quality filters.

The study participants didn’t know whether they were on a clean air drive or a roadway air drive. Breathing polluted air led to blood pressure increases of over 4.50 millimetres of mercury when compared to driving with the filters. And the increase occurred quickly, peaking an hour into the drive and holding steady for a full day.

The magnitude of the increase is similar to the impact of a diet high in sodium. “We know that modest increases in blood pressure like this, on a population level, are associated with a significant increase in cardiovascular disease,” Kaufman said. “There is a growing understanding that air pollution contributes to heart problems.”

The fact that roadway air pollution at relatively low levels can affect blood pressure to this extent is an important finding to better understand the effects of air pollution. The findings also raise questions about ultrafine particles, the researchers said. These are unregulated and little-understood pollutants that have become a source of concern.

Ultrafine particles measure less than 100 nanometers in diameter, too small to be seen. They are commonly detected in traffic-related air pollution, and in the study, the researchers found that the unfiltered air had high levels of these particles. This suggests that they may be very important in affecting blood pressure, but this will require further research.

“This study takes the gold-standard design for laboratory studies and applies it in an on-roadway setting, answering an important question about the health effects of real-world exposures,” Michael Young, study author, said in a news release. “The findings can reproduce situations that millions of people actually experience every day.”

The study was published in the Annals of Internal Medicine.