By Evan Bush - NBC News
Air polluted by fumes expelled by cars during traffic hours can sharply raise people's blood pressure almost from the moment they start traveling, a study that tracked people on busy roads in real time has revealed.
The results, published Monday in the Annals of Internal Medicine, suggest that highway pollution not only poses risks that accumulate over time, but also causes almost immediate changes in people's physiology. The research provided indications that sitting in traffic could contribute to triggering diseases such as heart attacks and strokes, although more studies are needed to establish clear links.
The study is the first to measure both pollution and its effect on blood pressure in real time from inside a moving vehicle. Investigators monitored both aspects dozens of times in Seattle traffic.
Vehicles travel amid smoke and a sandstorm in Beijing, April 13, 2023.Bloomberg via Getty Images
"We were surprised by the magnitude of the changes in blood pressure, given the low levels of pollution we measured," said Dr. Joel Kaufman, a professor of medicine, epidemiology and environmental health sciences at the University of Washington and an author of the study.
The results of the study included data from just 13 people, but they add to a long list of research that underscores growing concern about the health hazards posed by pollution on U.S. roads, particularly from tailpipe emissions and tire wear.
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"This study adds to a growing body of evidence that air pollution on and near roads is dangerous to health," said Doug Brugge, professor and chair of the Department of Public Health Sciences at the University of Connecticut, who was not involved in the study. "Driving on the road — commuting to work, driving in heavy traffic — is an understudied concern that deserves more attention."
To assess how traffic air pollution affects people, the researchers sent people on two-hour trips on Seattle's public roads, including Interstate 5.
The vehicle was fitted with a more powerful air filter than most cars usually have. A device to filter the air was placed in the passenger seat, pollution control equipment was placed in the back seat and a device to monitor the participants' blood pressure was installed on the drivers' fingertips, Kaufman said.
On some trips, the filters worked, and on others, they were fake. Participants never knew if the filters were working properly or not. When the air filters did their job, the devices reduced particulate pollution inside the vehicle by 86%, on average.
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Pollution levels were never terrible. On trips where the dummy filters were used, the average air quality index inside the car was just 36, which would earn it a "low" rating from air quality agencies, according to Kaufman.
Each participant made three trips: one with the actual filters and two without. The researchers found that, on average, people's blood pressure levels increased significantly — about 4.5 mm on the mercury stick, a measure of pressure — when the filters weren't working.
"It's a significant increase," said Brugge, who researches ultrafine particulate matter that is unregulated in the U.S. and may play a major role in the health effects of pollution in areas near highways.
Kaufman said doctors often advise people with high blood pressure to follow a low-sodium diet or avoid certain medications. The increase in blood pressure seen during hours in traffic when the air was not filtered is almost equivalent to the effect of those prophylactic measures, but in the opposite direction, he said.
The study has limitations. It only included the results of 13 people, and the conditions during the journeys were similar but not identical. Brugge worries that factors such as the difference in noise or vibration in the rides could skew the study's data. In his opinion, more studies with more subjects are needed to confirm these results.
Researchers have linked traffic to heart attacks in the past. A study conducted in Germany revealed that the chances of having a heart attack were almost three times higher if you had been in a traffic jam during the previous hour. Previous laboratory studies have shown that people's blood pressure spikes after exposure to diesel fumes.
More than 8.3 million deaths a year worldwide can be attributed to air pollution, according to estimates from a study published Thursday in the BMJ (formerly called the British Medical Journal). According to the study, phasing out fossil fuels would prevent nearly two-thirds of those deaths.
According to Brugge, this type of research expands knowledge about the harmful effects of air pollution and its impact on the planet.
"Air pollution is one of the top five public health problems in the world," he said. "What they're looking at, and we've been studying, are additional air pollution problems that don't yet fall into that calculation."