A study by USC researchers found a strong association between clean air and a healthy brain. They also discovered that areas with high air pollution had more Alzheimer’s disease and cognitive decline residents.
USC studies have determined that one pollutant in particular called PM2.5 leads to poor brain health. Cars and factories emit this fine particulate which measures less than 2.5 micrometers in diameter. Once they enter the nose, the particles move into the brain past the blood-brain barrier. Usually, this barrier protects against dust and other foreign substances.
However, due to the minuscule size of PM2.5 particles, they quickly break this barrier. These particles can also exacerbate lung disorders, penetrating deeply into the lungs and impairing lung health.
Fortunately, the USC-led research shows that improvements in air quality have lowered Alzheimer’s risk in certain areas. They published their findings in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association.
In their research, the USC team explained that their labs reported recent drops in the neurotoxicity of PM2.5 air pollution in both humans and mice. Neurotoxicity occurs when exposure to natural or artificial chemicals causes abnormal activity in the brain or nervous system. This means that more people have a healthy brain because of improved air quality.
University Professor Caleb Finch and associate professor of gerontology and sociology Jennifer Ailshire took part in the research. They’re both with the USC Leonard Davis School of Gerontology. They focused their investigation on PM2.5 pollution in particular to document its effects on brain health. Long-term exposure to PM2.5 can lead to early death, especially in people with chronic heart or lung disease.
USC Research Links Breathing Clean Air to a Healthy Brain
A 2004 study from Ailshire found a strong link between cognitive decline and air pollution in less-educated populations. Adults 65 and older with less than eight years of education had a higher risk of neurodegenerative disease when exposed to PM2.5. However, ten years later, Ailshire no longer found this association in the study participants. She based these findings on data from the nationwide Health and Retirement Study.
Ailshire believes that reduced PM2.5 emissions during the past decade increased their likelihood of having a healthy brain. Air quality data revealed that average annual PM2.5 levels in the participants’ cities dropped 25% since 2004.
In 2014, only a handful of the participants lived in areas with annual average PM2.5 levels that surpassed EPA regulations. This provides further evidence that reduced exposure to air pollution in older adults leads to a healthy brain.
“Improving air quality around the country has been a tremendous public health and environment policy success story. But there are signs of a reversal in these trends,” Ailshire said. “Pollution levels are creeping up again, and there are increasingly more large fires, which generate a significant amount of air pollution in certain parts of the country. This gives me cause for concern about future trends in improving air quality.”
Finch also published research on mice earlier this year in the Journal of Alzheimer’s Disease. The findings provide further proof that lower air pollution leads to a healthier brain in the long term.
Finch and his team have been observing how pollution affects the brains of mice at a Los Angeles site since 2009. In 2017, the mice exposed to a tiny, nanoscale type of PM2.5 seemed to have a healthier brain. What’s more, they also had significant declines in several measures of neurotoxicity, including oxidative damage to cells and tissues.
Study Shows Importance of Continued Improvements in Air Quality
During Finch’s and Ailshire’s studies, the composition of air pollution in the United States began to change. According to the EPA, from 2000 to 2020, PM2.5 levels decreased across the country by 41%.
However, PM2.5 in Los Angeles declined very little from 2009 to 2019. In this period, ozone levels in the United States decreased overall. However, it increased in Los Angeles County. Before 2015, ozone dropped in LA County following the national trend.
Overall, the study results are encouraging, showing that lower air pollution leads to a healthy brain and better memory. However, the authors stress that they can’t evaluate the possible benefits of air quality improvement to risks of cognitive decline. While PM2.5 levels fell across the US from 2009 to 2016, they’ve increased each year since 2017. This shows that air quality can fluctuate based on regulations and emission levels, like Los Angeles County.