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Experts say air pollution can affect people who live near freeways. Amos Chapple/Stocksy
  • Traffic-related air pollution was associated with a significant increase in blood pressure among car passengers, a study finds.
  • Researchers report that the blood pressure increase is on par with other cardiovascular risk factors such as lack of exercise or excessive salt intake.
  • Experts note that cabin air filters and other filtration devices, including masks, can lower exposure to dangerous air pollution particles.

People wearing masks while driving alone in their cars may not be so foolish after all.

The N95 masks used to help prevent the spread of COVID-19 might also filter out highway air pollution that a new study says can cause a serious and sustained spike in blood pressure.

The study, published in the Annals of Internal Medicine, reports that riding in automobiles and breathing unfiltered air was associated with a 4.5 mm Hg increase in blood pressure.

The blood pressure increase from exposure to traffic-related air pollution (TRAP) was found to peak within 60 minutes and persist for up to 24 hours, according to researchers from the University of Washington.

Dr. Joel Kaufman, a study corresponding editor and a University of Washington professor, epidemiologist, and environmental health expert, told Medical News Today:

“Traffic-related air pollution, even at levels now considered low, appears to cause a substantial increase in blood pressure. This is an effect of breathing traffic-related particles since it was not from the stress of being in a car, driving a car, or noise; the study design is able to account for all those things by using sham filtration vs real filtration, and the subjects were passengers and not drivers.”

Dr. John Higgins, a sports cardiologist at the McGovern Medical School at UTHealth in Houston who was not involved in the study, told MNT the study findings suggest that daily commuters breathing unfiltered highway air pollution could be experiencing dangerously elevated blood pressure throughout the workweek and perhaps even more if they drive on the weekends as well.

“It was stunning how quickly this led to a rise in blood pressure and that it persisted for so long,” Dr. Higgins said.

Kaufman noted, “Our group has previously showed that diesel exhaust exposure increased blood pressure. The roadway traffic study was designed to test those findings in a real-world setting by isolating the effects of traffic-related air pollution (TRAP).”

TRAP may include ultrafine particles known as PM 2.5, black carbon, oxides of nitrogen, carbon monoxide, carbon dioxide, and other particulate matter.

According to the Environmental Protection Agency (EPA), past studies have suggested that PM 2.5 particles are linked to a wide range of cardiovascular problems, including:

  • heart attacks
  • irregular heartbeat
  • asthma
  • other breathing problems
  • premature death

“PM 2.5 particles can get through the lining of blood vessels and into the circulatory system, affecting the heart and vascular tone, including arterial stiffness,” Dr. Loren Wold, a researcher and professor at The Ohio State University Wexner Medical Center who studies the cardiovascular effects of air pollution, told MNT. “That’s what causes elevated blood pressure.”

In the experimental study, researchers drove 16 subjects ages 22 to 45 years of age through traffic in Seattle, Washington, for three days.

For two days, unfiltered air was allowed to flow into the vehicle. On the third, a HEPA filter was installed.

Study subjects did not know whether the car had a HEPA filter — which can screen out dangerous PM 2.5 particles along with other pollutants — or an ineffective sham filter.

Blood pressure was monitored up to 24 hours before, during, and after the drives.

Dr. Kaufman and his colleagues found that the drives in vehicles with unfiltered TRAP were associated with significant net increases in blood pressure compared with drives with HEPA in-vehicle filtration.

Researchers said the 4.5 mm Hg rise in blood pressure detected was significant. For every 20 mm Hg systolic or 10 mm Hg diastolic increase in blood pressure, mortality from heart disease and stroke doubles.

Dr. Higgins said the TRAP-related blood pressure increase detected in the study was similar to that caused by poor diet, lack of activity, or smoking.

“These are the size of effects from things like salt in the diet that are well-known to increase blood pressure,” said Dr. Kaufman.

“Elevated blood pressures are major risk factors for heart disease, stroke, and kidney disease. The concern is partly for each individual, but [also the impact on the whole population. The overall effect of millions of people having these exposures is probably a lot of otherwise preventable cases of stroke, heart attacks, heart failure, and kidney disease.”

The study also demonstrated that the effects of air pollution on blood pressure may be reduced with effective cabin air filtration, Dr. Kaufman said.

“Maybe we need to think about high efficiency particulate air (HEPA) filters in automobiles or cities doing something about air pollution,” Dr. Higgins said.

However, most cars are not equipped with HEPA filters, nor are such passenger cabin air filters available for every make and model of automobile.

“Regular filters don’t work that well in the car, as you can tell when you can smell the exhaust from another vehicle with a bad muffler on the road,” noted Dr. Higgins.

“A good practice is to change the cabin air filter in your car just like you do the in-house filter on your furnace,” about once a year, said Dr. Wold.

Dr. Wold added that while a HEPA cabin air filter would be ideal, even a regular filter can eliminate some PM 2.5 sized particles, especially if the car’s climate control system is set to recirculate cabin air rather than bringing in air from outside the vehicle.

And yes, wearing an N95 mask while driving can also filter out PM 2.5 air pollution particles as well as preventing the spread of communicable diseases such as COVID-19.

The study also highlights the potential health risks of TRAP exposure among people other than automobile drivers or passengers, such as those who live close to highways, factories, or airports, said Dr. Kaufman.

Dr. Edo Paz, a cardiologist and senior medical vice president of medical affairs at the online cardiovascular health company Hello Heart, told MNT there is “some clinical evidence that air filtration in indoor environments is associated with decreases in blood pressure within two weeks.”

Dr. Wold noted that homeowners in communities with high levels of TRAP can increase the efficiency of their furnace HEPA filters by setting the system to circulate air every 15 minutes or so, rather than turning on the blower only when the heat or air conditioning comes on.

“Any smart thermostat should allow you to set your system on continuous circulation,” he said.