Mental health has been a growing concern in the United States in recent years. That’s not surprising, as nearly one in five Americans suffers from some mental illness every year. 42.5 million American adults deal with conditions like depression, bipolar disorder or schizophrenia, according to statistics published in 2014. While there are many things that may contribute to mental illness, one of them is very “out of sight, out of mind” — air quality. A number of studies have been conducted to see how air pollution affect the brain. Many of these have linked air pollution to mental health issues such as depression, autism, and schizophrenia.
What kind of polluted air can affect the brain?
When cars, factories, and power plants burn fuel, they produce the carbon particles that make up most air pollution. For decades, research on the health effects of air pollution has focused on the part of the body where its effects are most obvious — the lungs. That research began to show that different-sized particles produce different effects. The Environmental Protection Agency (EPA) regulates larger particles. These are actually the least harmful, because they get coughed up and expelled. However, the EPA doesn’t regulate smaller particles known as ultrafine particles. These are more dangerous, because they are small enough to travel deep into the lungs. From there, they be absorbed into the bloodstream, and produce toxic effects throughout the body.
Air Pollution and Depression
In 2011, the Neuroscience Department at Ohio State University ran a study in mice. This study found that long-term exposure to air pollution can lead to physical changes in the brain. These changes can cause problems with learning and memory, and even depression. Laura Fonken was lead author of the study, and a doctoral student in the program. She said, “the results suggest prolonged exposure to polluted air can have visible, negative effects on the brain, which can lead to a variety of health problems. This could have troubling implications for people who live and work in polluted urban areas around the world.”
In this study, researchers exposed mice to either filtered air or polluted air. This went on for six hours a day, five days a week for 10 months. That’s nearly half the lifespan of the mice. The polluted air contained fine particulate matter, the kind of pollution created by cars, factories and natural dust. The fine particulates are tiny – about 1/30th of the average width of a human hair. Researchers exposed the mice to a concentration of particulate matter equivalent to polluted air people breathe in some polluted urban areas.
After 10 months of exposure to the polluted or filtered air, the researchers performed a variety of behavioral tests on the animals. In one experiment, mice exposed to the polluted air showed more depressive-like behaviors. In another test, the polluted-air mice showed signs of higher levels of anxiety-like behaviors.
How did the brain change?
In the Ohio State study, the researchers tested the hippocampal area of the mice brains to find the answers. Fonken said, “We wanted to look carefully at the hippocampus because it is associated with learning, memory and depression.” Results showed clear physical differences in the hippocampi of the mice who were exposed to the polluted air, compared to those who weren’t. In mice that breathed the polluted air, chemical messengers that cause inflammation – called pro-inflammatory cytokines – were more active in the hippocampus than they were in mice who breathed the filtered air. “The hippocampus is particularly sensitive to damage caused by inflammation,” Fonken said. “We suspect that the systemic inflammation caused by breathing polluted air is being communicated to the central nervous system.”
Autism and Schizophrenia
Deborah Cory-Slechta, Ph.D., professor of Environmental Medicine at the University of Rochester, ran a similar study on mice. This study revealed that exposure to air pollution in early life causes changes in the brain. This includes an enlargement of part of the brain that is seen in humans who are diagnosed with autism and schizophrenia. This supports other recent studies that highlight a strong correlation between air pollution and risk of autism in children. One study showed that children residing in areas with high levels of air pollution during their first year of life had a three-fold increase in the risk of autism.
Cory-Slechta’s study conducted three sets of experiments in which mice were exposed to levels of air pollution typically found in mid-sized U.S. cities during rush hour. Researchers conducted the exposures during the first two weeks after the mice were born. This is a critical time in the brain’s development. Researchers exposed the mice to the polluted air for four hours a day, for two four-day periods.
In one group of mice, researchers examined the brains 24 hours after the final pollution exposure. In all of those mice, inflammation was rampant throughout the brain. The lateral ventricles — chambers on each side of the brain that contain cerebrospinal fluid — were enlarged two-to-three times their normal size. Researchers observed the problems in a second group of mice 40 days after exposure and in another group 270 days after exposure. This indicated that the damage to the brain was permanent.
How did the brain change?
“When we looked closely at the ventricles, we could see that the white matter that normally surrounds them hadn’t fully developed,” said Cory-Slechta. “It appears that inflammation had damaged those brain cells and prevented that region of the brain from developing, and the ventricles simply expanded to fill the space.” Brains of mice in all three groups also had elevated levels of glutamate, a neurotransmitter. This is also seen in humans with autism and schizophrenia.
Air pollution might not be the most obvious concern regarding our mental health. However, there’s no question that the quality of the air we breathe has an effect on our brains. If we can keep air pollution in check, our communities, family and children will be healthier and happier.