Depressed? Fearful? Air pollution can be a factor

In the 1990s, residents of Mexico City noticed their dogs behaving strangely — some didn’t recognize their owners, and the animals’ sleeping patterns had changed.

At the time, the sprawling, mountain-ringed city of more than 15 million people was considered the world’s most polluted city, with a thick, constant fog of fossil fuel pollution trapped by thermal inversions.

In 2002, toxicologist and neuropathologist Lilian Calderón-Garcidueñas, who is affiliated with both the Universidad del Valle de México in Mexico City and the University of Montana, examined the brain tissue of 40 dogs living in the city and 40 others from a nearby one rural area with clean air. She discovered that the city dogs’ brains showed signs of neurodegeneration, while the country dogs had far healthier brains.

Calderón-Garcidueñas went on to examine the brains of 203 Mexico City residents, only one of whom showed no signs of neurodegeneration. This led to the conclusion that chronic exposure to air pollution can negatively affect people’s olfactory system at a young age, making them more susceptible to neurodegenerative diseases such as Alzheimer’s and Parkinson’s.

The pollutant that plays the “big role” is particulate matter, Calderón-Garcidueñas said. “Not the big ones, but the little ones who can overcome barriers. We can detect nanoparticles in neurons, in glial cells, in epithelial cells. We’re also seeing things that shouldn’t be there at all – titanium, iron and copper.”

The Mexican scientist’s work feeds a growing body of evidence showing that breathing polluted air not only causes heart and lung damage, but also neurodegeneration and mental health problems.

It is well known that air pollution takes a heavy 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 air pollution, which according to the World Health Organization tops the list of global health threats with 7 million deaths each year. Children and infants are particularly vulnerable.

Figuring out the effects of air pollution on the brain has been more difficult than other organs due to its inaccessibility, so it hasn’t been studied as thoroughly, according to researchers. Whether air pollution can cause or contribute to Alzheimer’s or Parkinson’s is not a proven science. But Calderón-Garcidueñas’ work is at the forefront of showing that air pollution, through the air we breathe, goes straight to the brain and has serious effects.

Some psychotherapists report seeing patients with symptoms attributed to air pollution. Pollution doesn’t just seem to cause or worsen symptoms; it also takes away forms of relief.

“When we exercise and spend time in nature, we become extra resilient,” said Kristen Greenwald, environmental social worker and associate professor at the University of Denver. “A lot of people do it outside. This is their coping mechanism; it is calming for the nervous system.”

On dirty days, “many of their customers can’t go outside without feeling like they’re feeling even sicker or more desperate.”

Megan Herting, who researches the effects of air pollution on the brain at the University of Southern California, said environmental factors should be included in doctors’ assessments these days, especially in places like Southern California and Front Range in Colorado where air pollution is high and chronic Problem.

“When I go to a medical clinic, they rarely ask me where I live and what my home environment is like,” she said. “Where we live, what we are exposed to is important to think about prevention and treatment.”

Over the past two decades, research into air pollution and its effects on the human nervous system has skyrocketed with new technologies.

Research shows that tiny particles bypass the body’s filtration systems when inhaled through the nose and mouth and go straight to the brain. Fine and ultrafine particles, such as those found in diesel exhaust, soot, dust and wildfire smoke, often contain metals that interfere with hitchhiking and make it less effective.

A changing climate is likely to worsen the effects of air pollution on the brain and mental health. Warmer temperatures react with car tailpipe emissions to produce more ozone than is produced when it is cooler. And more and bigger wildfires are expected to mean more smoky sky days.

Ozone has been linked to neurodegeneration, decreases in cerebral plasticity, neuron death, and learning and memory disorders. Ozone levels are extremely high in Los Angeles and the western mountain valleys, including the Front Range of Colorado, Phoenix and Salt Lake City.

Air pollution also causes damage from chronic inflammation. When air pollution particles enter the brain, they are mistaken for germs and attacked by microglia, a component of the brain’s immune system, and remain activated.

“Your body doesn’t like being exposed to air pollution, and it creates an inflammatory response,” Patrick Ryan, a researcher at Cincinnati Children’s Hospital, said in an email. “Your brain doesn’t like it either. There are more than 10 years of toxicological science and epidemiological studies showing that air pollution causes neuro-inflammation.”

Much of the current research focuses on how pollution causes mental health problems.

Damage to the brain is particularly harmful as it is the body’s main control board and environmental damage can cause a range of neuropsychiatric disorders. A major focus of research today is how pollution-related damage affects areas of the brain that regulate emotions—such as the amygdala, prefrontal cortex, and hippocampus. For example, the amygdala governs the processing of fearful experiences, and its impairment can cause anxiety and depression. In a recent review, 95% of studies looking at physical and functional changes in areas of the brain that regulate emotions showed an effect of air pollution.

A very large study published in February in JAMA Psychiatry by researchers from Oxford University, Beijing University and Imperial College London tracked and found the onset of anxiety and depression in nearly 400,000 UK adults over a median of 11 years found Long-term exposure to even low levels of a combination of air pollutants—particulate matter, nitrogen dioxide, and nitric oxide—increased the incidence of depression and anxiety.

Another recent study by University of Denver’s Erika Manczak found that adolescents exposed to ozone are predicted “for a steeper rise in depressive symptoms throughout adolescent development.”

But epidemiological research has flaws due to confounders that are difficult to explain. Some people are genetically predisposed to susceptibility and others are not. Some may suffer from chronic stress or be very young or very old, which can increase their vulnerability. People who live near greenery, which reduces anxiety, may be less susceptible.

“People living in areas where they are more exposed to pollutants tend to be underserved in many ways and struggle with many systemic problems. There are bigger reports of stress, depression and anxiety,” Manczak said. “Given that these areas have been marginalized for many reasons, it’s hard to say that this is due to exposure to air pollution.”

The best way to know for sure would be to conduct clinical trials, but that brings with it ethical issues. “We cannot indiscriminately expose children to air pollution,” Ryan said.

KFF health news is a national newsroom producing in-depth journalism on health issues and is one of the core programs of KFF — the independent source for health policy research, polls and journalism.

Justin Scaccy

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