Take the scenic route: Rush hour traffic spikes blood pressure as much as high-sodium diet

SEATTLE — Concerning new findings suggest the countless commuters who travel on high-traffic highways every day may be putting their cardiovascular health at risk. Scientists at the University of Washington report that unfiltered air from rush-hour traffic appeared to significantly increase passengers’ blood pressure — both while in the car and up to 24 hours later!

Sprawling, interconnected highways and roadways have been a common sight across virtually every urban area in the United States for decades upon decades, but scientists are only now beginning to fully grasp all of the health risks posed by the air pollution generated by all of those cars. Recent years have seen studies find that long-term exposure to traffic-related air pollution is linked to higher rates of heart disease, lung cancer, asthma, and death. What exactly is traffic-related air pollution? Researchers explain it as a complex mixture of exhaust from tailpipes, brake and tire wear, and road dust.

Now, this latest project indicates those health risks are also common in people habitually traveling on busy roads.

“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,” says Joel Kaufman, a UW physician and professor of environmental and occupational health sciences who led the study, in a media release.

An earlier experiment performed in Kaufman’s lab had already found that exposure to diesel exhaust fumes can increase blood pressure in a controlled environment. The roadway traffic study, meanwhile, was put together to test that finding in a real-world setting by isolating the effects of traffic-related air pollution.

Traffic in the city
Sitting in rush hour traffic can raise your blood pressure — and it’s not because of the stress. (Credit: Pixabay from Pexels)

Study authors drove a group of healthy participants (ages 22-45 years old) through rush-hour Seattle traffic while monitoring their blood pressure. During two of the trips, unfiltered road air was allowed to enter the car. This was done to mimic or recreate precisely how many people drive in real-life. During the third trip, the car was equipped with high-quality HEPA filters that blocked out 86 percent of particulate pollution. The entire time, participants were unaware whether they were on a clean air drive or a roadway air drive.

Consequently, breathing in unfiltered air resulted in net blood pressure increases among subjects of over 4.50 mm Hg (millimeters of mercury) in comparison to drives with cleaner, filtered air. This increase usually happened in a rapid manner, peaking about an hour into the drive and then subsequently remaining steady for the following 24 hours, at least. Study authors did not test past the 24-hour mark.

Incredibly, findings show the size of the observed increase is comparable to the effect of a high-sodium diet.

“We know that modest increases in blood pressure like this, on a population level, are associated with a significant increase in cardiovascular disease,” Prof. Kaufman explains. “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.”

These findings also raise questions regarding ultrafine particles, which are an unregulated and little-understood pollutant that have become a source of growing concern among many public health experts. Ultrafine particles are less than 100 nanometers in diameter, meaning they are much too small to be seen by the human eye.

Traffic-related air pollution contains high concentrations of ultrafine particles. During this study, unfiltered air contained high levels of ultrafine particles. However, the overall level of pollution as measured by fine particle concentration (PM 2.5) was relatively low, equivalent to an AQI of 36.

“Ultrafine particles are the pollutant that were most effectively filtered in our experiment – in other words, where the levels are most dramatically high on the road and low in the filtered environment,” Prof. Kaufman adds. “So, the hint is that ultrafines may be especially important [for blood pressure]. To actually prove that requires further research, but this study provides a very strong clue as to what’s going on.”

Traffic-related air pollution is considered the main driver of air quality variation from community to community across the cast majority of U.S. metropolitan areas.

“This study is exciting because it 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. Studies on this topic often have a challenging time separating the effects of pollution from other roadway exposures like stress and noise, but with our approach the only difference between drive days was air pollution concentration,” concludes Michael Young, a former UW postdoctoral fellow in the Department of Environmental and Occupational Health Sciences and lead author of the new study. “The findings are valuable because they can reproduce situations that millions of people actually experience every day.”

The study is published in Annals of Internal Medicine.

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John Anderer

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  1. I imagine sitting for long periods of time can also have a detrimental effect on circulation and thus blood pressure. Other impacts that may lead to stress in driving in traffic is the impact of randomization of other drivers, the stress of remaining ultra aware and cautious might release stress hormones that could impact our blood pressure. Third, I would think the surroundings of the driver might also impact the experience and thus possibly blood pressure, such as temperature of the car cabin (too cold or too hot) or sunlight exposure (tinted windows or sunglasses).

  2. So shouldn’t people who don’t work from home and are required to travel in heavy traffic daily for their job be compensated for this extra hazzard.

    1. No. In a 2012 conference paper I showed that in a peak lasting 1 hour, each added vehicle adds at least 30 minutes delay to the total, which is far more than the delay that vehicle experiences at any realistic level of demand over capacity. On the contrary, they should be charged a toll. However, if by reducing the traffic that reduces the risk of harm to those who choose to pay, it may be worth it.

  3. I drive cars for an auction company three days a week. Not only in heavy traffic areas, but the average distance is 100 miles one way. I have been experiencing high blood pressure recently and am currently on four prescriptions.

  4. All I know is, when im going the speed limit or over and am still getting tailgated, my blood pressure spikes. When im driving and people coming the other way try to hog the road by driving in my lane, my blood pressure spikes. When I have people at night riding my rear with their bright lights on, my blood pressure spikes. It spikes so much sometimes, that I feel an almost irresistible urge to drag drivers out of their cars or trucks and beat them to death.

  5. I got a fitness tracker a couple of years ago. I soon noticed that my heart rate and blood pressure spiked at about the same times every day. It was the times that I was merging onto the evil 91 freeway in Southern California for my daily commute.

  6. My blood pressure rises more thinking of the black hole money put of Sound Transit in Seattle & Tacoma. Coupled with delays and the crime, filth & drug use, it’s surprising there aren’t more heart attacks on the train. ✌️

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