(Oona Tempest / KFF Health News)
In the 1990s, residents of Mexico City noticed their dogs acting strangely — some didn’t recognize their owners, and the animals’ sleep patterns had changed.
At the time, the sprawling, mountain-ringed city of more than 15 million people was known as the most polluted in the world, with a thick, constant haze of fossil fuel pollution trapped by thermal inversions.
In 2002, toxicologist and neuropathologist Lilian Calderón-Garcidueñas, who is affiliated with both Universidad del Valle de México in Mexico City and the University of Montana, examined brain tissue from 40 dogs that had lived in the city and 40 others from a nearby rural area with cleaner air. She discovered the brains of the city dogs showed signs of neurodegeneration while the rural dogs had far healthier brains.
Calderón-Garcidueñas went on to study the brains of 203 human residents of Mexico City, only one of which did not show signs of neurodegeneration. That led to the conclusion that chronic exposure to air pollution can negatively affect people’s olfactory systems at a young age and may make them more susceptible to neurodegenerative diseases such as Alzheimer’s and Parkinson’s.
The pollutant that plays the “big role” is particulate matter, said Calderón-Garcidueñas. “Not the big ones, but the tiny ones that can cross barriers. We can detect nanoparticles inside neurons, inside glial cells, inside epithelial cells. We also see things that shouldn’t be there at all — titanium, iron, and copper.”
The work the Mexican scientist is doing is feeding a burgeoning body of evidence that shows breathing polluted air not only causes heart and lung damage but also neurodegeneration and mental health problems.
It’s well established that air pollution takes a serious toll on the human body, affecting almost every organ. Asthma, cardiovascular disease, cancer, premature death, and stroke are among a long list of problems that can be caused by exposure to air pollution, which, according to the World Health Organization, sits atop the list of health threats globally, causing 7 million deaths a year. Children and infants are especially susceptible.
Sussing out the impact of air pollution on the brain has been more difficult than for other organs because of its inaccessibility, so it has not been researched as thoroughly, according to researchers. Whether air pollution may cause or contribute to Alzheimer’s or Parkinson’s is not settled science. But Calderón-Garcidueñas’ work is at the leading edge of showing that air pollution goes directly into the brain through the air we breathe, and has serious impacts.
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Some psychotherapists report seeing patients with symptoms stemming from air pollution. Not only does the pollution appear to cause symptoms or make them worse; it also takes away forms of relief.
“If we exercise and spend time in nature we become extra resilient,” said Kristen Greenwald, an environmental social worker and adjunct professor at the University of Denver. “A lot of folks do that outside. That’s their coping mechanism; it’s soothing to the nervous system.”
On polluted days a lot of her clients “can’t go outside without feeling they are making themselves more sick or distressed.”
Megan Herting, who researches air pollution’s impact on the brain at the University of Southern California, said environmental factors should be incorporated in doctors’ assessments these days, especially in places like Southern California and Colorado’s Front Range, where high levels of air pollution are a chronic problem.
“When I go into a medical clinic, they rarely ask me where I live and what is my home environment like,” she said. “Where are we living, what we are exposed to, is important in thinking about prevention and treatment.”
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