Breathing in dirty air damages our lungs, but new research is showing it might change how we think, too.
A study published earlier this week in the Proceedings for the National Academy of Sciences found that long-term exposure to particulate matter, sulfur dioxide, and nitrogen dioxide led to cognitive declines in study participants as they aged. Less-educated men were particularly impacted and had low verbal and math test scores.
Scientists and health officials are still working to discern exactly how air pollutants interact with the brain.
“We speculate that air pollution probably puts greater damage on the white matter in the brain, which is associated with language ability,” says Xin Zhang, a study author and researcher at Beijing Normal University's school of statistics.
Previous studies have found that female brains on average have more white matter than male brains, meaning damage to white matter would put males, with lesser white matter, more at risk of experiencing cognitive declines.
“More research is needed to understand the mechanisms,” notes Zhang.
While the Chinese study highlights an important link, it will need to be replicated to quantify how air pollution changes the brain, says Jonathan Samet, dean of the Colorado School of Public Health. Only in the past decade has research on air pollution and brain health intensified, he says, noting that how particles enter and coat the lungs is better understood.
“The lungs are the portal of entry,” says Samet. “The area of the lungs is the size of the tennis court, so there's a huge surface to hit. We breathe in 10,000 liters [of air] a day.”
Like Zhang, Samet says that more research needs to be done to understand the exact mechanisms of how pollution particles enter the brain, what functions they impact, and how long they last once there.
“They could move along the olfactory nerves from the nose to the brain, or they get into the blood,” says Samet. He suspects that damage could also be caused by inflammation.
In addition to the lungs and the brain, studies have also linked air pollution with poor heart health and diabetes.
“It's surprising how many organs seem to be affected,” Samet adds.
As environmental toxicologist Dan Costa from the University of North Carolina explains, that’s because the human body's internal makeup is highly interconnected. Air pollution has been shown to minimally impact not just the lungs, but the heart, brain, and reproductive system.
“When something comes in [to the body] that's potentially toxic, it's implications are everywhere,” he says. His suspects that pollutants reach the brain through the blood stream.
All of the blood that leaves the lungs goes through the heart, where it's then pumped out to the rest of the body. Costa suspects this triggers the immune system, causing inflammation. Over time, he says, too many toxic particles could cause too much inflammation, which may accelerate how quickly the brain ages.
The brain is a difficult organ to study, notes Costa. And this relatively new research frontier is made more difficult because of the numerous variables that can alter brain chemistry.
“The brain has such a complex network of processes,” Costa adds. “It has a higher level of functionality that the other organs don't.”
Air Pollution Today
People today live longer than they did 70 years ago, when black soot was pumped into the atmosphere. Costa says this could at least partially account for why doctors are just now seeing all the ways air pollution permeates through the body.
“We didn't appreciate the subtleties that are emerging now,” he adds.
Costa, who until recently worked at the U.S. Environmental Protection Agency, says particulate matter, which is generated by anything from wildfires to fossil fuel combustion, is largely thought to be the air pollutant most dangerous to health. But pinpointing the impacts of any one particle can be difficult because regions with poor air quality often have more than one type of pollutant.
In the past two decades, EPA data shows the three pollutants identified in the Beijing study have all decreased in the U.S. They remain, however, in developing regions with large urban industrial centers.
In a report published this year, the World Health Organization published a report finding nine in 10 people globally breath bad air. In the U.S., the American Lung Association puts that number at four in 10.
“We're getting to the point where a lot of easy wins have been done,” says Samet. Coal burning power plants and diesel generators remain some of the most dangerous source of air pollution.
Samet suspects that tackling other forms of air pollution will require a change in mindset in the form of improved public transportation or better city planning.