Tag: Jiu-Chiuan Chen

Air pollution may contribute to Alzheimer’s and dementia risk – here’s what we’re learning from brain scans

Jiu-Chiuan Chen, University of Southern California

Alzheimer’s disease is the most common cause of dementia. It slowly destroys memory, thinking and behaviors, and eventually the ability to carry out daily tasks.

As scientists search for a cure, we have been learning more about the genetic and environmental factors that can increase a person’s risks of developing late-onset Alzheimer’s disease and related dementias.

In particular, my colleagues and I in preventive medicine, neurology and gerontology have been looking at the role of outdoor air pollution.

Our early research in 2017 became the first study in the U.S. using both human and animal data to show that brain aging processes worsened by air pollution may increase dementia risk. Our latest studies show how older women who lived in locations with high levels of PM2.5 – the fine particulate matter produced by vehicles and power plants – suffered memory loss and Alzheimer’s-like brain shrinkage not seen in women living with cleaner air.

Together these findings suggest a way to avoid one risk factor for Alzheimer’s disease – reduce human exposure to PM2.5. Unfortunately, that’s easier said than done.

Silent risk for dementia

PM2.5, also known as soot, consists of microscopic particles of chemicals, car exhaust, smoke, dust and other pollutants suspended in the air. An estimated one in six Americans lives in counties with unhealthy levels of particle pollution.

We have been investigating whether PM2.5 may accelerate the brain’s aging processes at the preclinical stage – the “silent” phase of the disease before any symptoms of Alzheimer’s disease and related dementias appear.

In the first U.S.-based nationwide study to link PM2.5 exposure and cognitive impairment, published in 2017, we found older women were almost twice as likely to develop clinically significant cognitive impairment if they had lived in places with outdoor PM2.5 levels exceeding the U.S. Environmental Protection Agency’s standard than if they hadn’t. Because we worked with the Women’s Health Initiative Memory Study, which followed the participants closely, we were able to account for other dementia risk factors, such as smoking, lack of exercise and hormone therapy.

Illustration showing how a brain with Alzheimer's disease shrinks.
The brain atrophies with Alzheimer’s disease. National Institute On Aging

In a new study, we wanted to see how the brains of older people were changing if they had experienced different levels of PM2.5 in the years before Alzheimer’s symptoms began.

We followed the progress of 712 women with an average age of 78 who did not have dementia at the start of the study and who underwent MRI brain scans five years apart. By combining EPA monitoring data and air quality simulations, we were able to estimate the everyday outdoor PM2.5 level around where the participants lived before their first MRI scan.

We found older women were more likely to have brain shrinkage similar to what is observed in patients with Alzheimer’s disease. When we compared the brain scans of older women from locations with high levels of PM2.5 to those with low levels, we found dementia risk increased by 24% over the five years.

Perhaps more alarming is that these Alzheimer’s-like brain changes were present in older women with no memory problems. The shrinkage in their brains was greater if they lived in locations with higher levels of outdoor PM2.5, even when those levels were within the current EPA standard.

Researchers in Spain recently examined brain MRI scans of healthy individuals at risk for Alzheimer’s disease and also found associations between air pollution exposure and reduced volume and thickness in specific brain areas known to be affected in Alzheimer’s disease.

Pollution and brain shrinkage

We also looked at episodic memory, which involves memories of specific events and is affected early by Alzheimer’s disease. If episodic memory decline was associated with living in locations with increasing PM2.5, could we see any evidence that such specific cognitive decline came as a consequence of the Alzheimer’s-like brain shrinkage?

Data from the Women’s Health Initiative Memory Study and past MRIs allowed us to look for changes across time for nearly 1,000 women. We found that as outdoor PM2.5 increased in locations where these older women lived, episodic memory declined. Approximately 10%-20% of the greater memory decline could be explained by Alzheimer’s-like brain shrinkage.

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Because the silent phase of dementia is thought to start decades before the manifestation of symptoms, findings from our recent studies raise concerns that air pollution exposures during mid to early life may be equally or even more important than late-life exposure.

How Alzheimer’s changes the brain. National Institute On Aging.

Genes also appear to play a role. Our research has shown that a critical Alzheimer’s risk gene, APOE4, interacts with air particles to accelerate brain aging. We found the environmental risk raised by long-term PM2.5 exposure was two to three times higher among older women with two copies of the APOE4 gene than among women without the gene.

Other researchers have subsequently investigated the possible interplay of that gene and environment. A Swedish study in 2019 did not find strong evidence for gene and environment interaction. But a 2020 study using data collected from elderly residents of two New York City neighborhoods found an association between long-term air pollution exposure and cognitive decline, with steeper rates of decline found in APOE4 carriers.

An avoidable risk

In the U.S., the Clean Air Act requires the Environmental Protection Agency to develop air quality standards that provide an adequate margin of safety to protect sensitive populations, such as children and the elderly.

The U.S. government had an opportunity to strengthen those standards in 2020, a move that EPA scientists explained could prevent thousands of premature deaths from health risks such as heart disease. Scientists advocated tougher standards, citing other health problems linked to PM2.5. However, EPA Administrator Andrew Wheeler declined, announcing on Dec. 7 that the standards would remain unchanged.The Conversation

Jiu-Chiuan Chen, Associate Professor of Preventive Medicine, University of Southern California

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Two new studies explore how pollution affects the brain

USC researchers are investigating the impact of fine particle pollution on child brain growth and in older women who aren’t eating enough fish.

Fine particle pollution can alter a child’s brain. (Illustration/iStock)

A pair of recently published USC studies add to our growing understanding of how fine particle pollution — the tiny, inhalable pollutants from cars and power plants — impacts our brains.

The first study, published in Environment International, found that these fine particles — known as PM2.5 — may alter the size of a child’s developing brain, which may ultimately increase the risk for cognitive and emotional problems later in adolescence.

“At this young age, the neurons in children’s brains are expanding and pruning at an incredible rate. As your brain develops, it wants to create efficient pathways,” said lead author Megan Herting, an assistant professor at the Keck School of Medicine of USC. “If these pathways are altered by PM2.5 exposure, and different parts of the brain are maturing and making connections at different rates, that might set you up for individual differences later on.”

USC, located in what the American Lung Association frequently cites as the most polluted city in the nation, is home to a robust air pollution research program. Findings from its studies have led to changes in state and federal guidelines to improve air quality standards. One of its cornerstones is the USC Children’s Health Study, one of the largest and most detailed studies of the long-term effects of air pollution.

Herting’s team used MRI scans from nearly 11,000 children aged 9 and 10 from 21 cities across the United States and matched each scan with yearly pollution data for each child’s residence. This is the first study of its kind to show that, even at relatively low levels, current PM2.5 exposure may be an important environmental factor that influences patterns of brain development in American children.

When they compared highly exposed kids with those who had less exposure to PM2.5, they saw differences. For example, areas associated with emotion were larger in highly exposed kids, while other areas associated with cognitive functioning were smaller.

Herting plans to follow the progress of the children, who are part of the ABCD Study, the largest long-term study of brain health and child development in the United States.

Eating fish could help protect women’s brains against fine particle pollution

The second study, published in Neurology, found that omega-3 fatty acids from consuming fish may protect against PM 2.5-associated brain shrinkage in older women.

Previous USC research showed that women in their 70s and 80s who were exposed to higher levels of air pollution experienced greater declines in memory and more Alzheimer’s-like brain atrophy than their counterparts who breathed cleaner air.

For this study, researchers looked at the brain MRIs of 1,315 women aged 65 to 80 and blood test results to determine levels of healthy omega-3 fatty acids in their blood.

“We found that women with higher blood levels of omega-3s had larger volumes of white matter in their brains. Women living in locations with higher PM2.5 tended to have smaller white matter in their brains, but such damage that may be caused by PM2.5 was greatly reduced in women with high blood levels of omega-3 fatty acids,” said corresponding author Jiu-Chiuan Chen, an associate professor at the Keck School of Medicine of USC.

The brain’s white matter, in contrast to gray matter, makes up most of the volume of the brain. It is the vast, intertwining system of neural connections that unites different regions of the brain that perform various mental operations. White matter loss may be an early marker of Alzheimer’s disease.

– By Leigh Hopper


About the Environment International study: In addition to Herting, other authors of the study include Dora Cserbik, Jiu-Chiuan Chen, Rob McConnell, Elizabeth R. Sowell, Daniel A. Hackman, all of USC; Kiros Berhane of Mailman School of Public Health of Columbia University; Eric Kan of Children’s Hospital Los Angeles; Joel Schwartz of Harvard T.H. Chan School of Public Health; and Chun C. Fan of UC San Diego.

The study was supported with grants from the National Institute of Environmental Health Sciences (P30ES007048-23S1, 3P30ES000002-55S1, P01ES022845), the Environmental Protection Agency (RD 83587201, RD 83544101) and the Rose Hills Foundation. The larger ABCD study is also supported by the National Institutes of Health (U01DA041048, U01DA050989, U01DA051016, U01DA041022, U01DA051018, U01DA051037, U01DA050987, U01DA041174, U01DA041106, U01DA041117, U01DA041028, U01DA041134, U01DA050988, U01DA051039, U01DA041156, U01DA041025, U01DA041120, U01DA051038, U01DA041148, U01DA041093, U01DA041089, U24DA041123 and U24DA041147).

About the Neurology study: In addition to Chen, other authors of the study include Xinhui Wang and Helena Chui of Keck; Cheng Chen and Ka He of Columbia University; Pengcheng Xun of Indiana University; Joel Kaufman of the University of Washington; Kathleen Hayden and Mark Espeland of Wake Forest School of Medicine; Eric Whitsel, Marc Serre and William Vizuete of University of North Carolina Chapel Hill; Tonya Orchard of Ohio State University; and William Harris of the University of South Dakota.

The study was supported with grants from the National Institutes of Health (R01AG033078, RF1AG054068 and RF1AG056111) and the National Institute of Environmental Health Sciences (R01ES025888).