Tag: Alzheimer’s

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.

USC, Mexico make strides in public health research

Jonathan Samet has partnered with many Mexican agencies on studies involving public health issues.

For more than 20 years, Jonathan Samet has developed strategies to prevent smoking in Mexico, with help from scientists and leaders at the country’s National Institute of Public Health (INSP).

The USC Distinguished Professor teams with several of Mexico’s 12 institutes of health, which aim to improve public health through research, policy and care. The INSP’s research centers and school of public health examine tobacco, obesity and other issues that contribute to health problems.

Samet assisted in the development of the institute’s Center for Tobacco Control Research and co-founded the Summer Program in Public Health, one of the largest of its kind in Latin America, with INSP Director Mauricio Hernández-Ávila. Samet has taught in the program every year since it began 22 years ago and has arranged for Trojans to teach there as well.

Building momentum

Since 2008, the year of Samet’s arrival at USC, the Department of Preventive Medicine has gained momentum in its research and scholarly exchanges with Mexico. Samet’s ties to INSP have enabled USC researchers to collaborate on various public health projects in the country and among Mexican and immigrant populations.

“The U.S. and Mexico share more than a border,” said Samet, holder of the Flora L. Thornton Chair in the Department of Preventive Medicine at the Keck School of Medicine of USC. “We share health challenges but also the expertise to combat them.”

In 2015, preventive medicine professors Lourdes Baezconde-Garbanati and Mary Ann Pentz founded the Center for Health Equity in the Americas to advance health equity in the region through research, training and partnerships. Using findings from an international summit in October, the group is working with INSP on a cervical cancer prevention report to be published in INSP’s journal, Salud Pública de Mexico, later this year.

Other centers in the department, including the Institute for Global Health, the Program on Global Health & Human Rights and the Immigrant Health Initiative, have hosted Mexican researchers and collaborators for talks, seminars and training on subjects, including sexually transmitted infectionsobesity, H1N1premature mortality and cervical cancer prevention.

Institute for Global Health Associate Director Heather Wipfli collaborated with INSP in 2016 to survey Mexican corporations about how health and wellness are integrated into their workplaces. The project is helping to inform the global cancer prevention programs begun by the American Cancer Society.

Another recent project, led by USC neurologist John Ringman and Mellissa Withers, assistant professor of clinical in the Department of Preventive Medicine, examined knowledge and attitudes regarding Alzheimer’s disease, genetics and participation in research among populations at-risk for a rare form of early onset familial Alzheimer’s disease in Mexico.

Fair exchange

In 2015, the Department of Preventive Medicine welcomed INSP postdoctoral fellow Katia Gallegos as part of an initiative with Mexico’s National Council of Science and Technology, in which USC provides scholars from Mexico with residencies in fields related to science, technology and innovation.

Gallegos is working with large binational data sets to determine the impact of acculturation in patterns of physical activity and sedentary behavior, as well as its association with body mass index observed in Mexicans, Mexican immigrants and Mexican-Americans. In addition, she is teaming with U.S. tobacco-use databases to study young people with mental illness who use multiple tobacco products.

Department researchers have also examined Mexico’s indoor smoking bancigarette sales tax, drug reform and teenagers’ smoking habits, as well as mental health risks and lower colorectal cancer susceptibility among Mexicans who migrated to the United States.

Along with Mexican and other U.S. scientists, USC researchers in 2013 discovered a genetic link associated with higher Type 2 diabetes risk among Mexican populations. Most recently, a study found that Latino children living in areas with higher levels of air pollution have a greater risk of developing Type 2 diabetes.

Career dedicated to public health

JonSametINSP-hw.jpg

Jonathan Samet accepts an honorary degree awarded by Mexico’s National Institute of Public Health. (Photo/Heather Wipfli)

Now celebrating its 30th anniversary, the INSP gave Samet an honorary doctorate recognizing his contributions to public health on Jan. 27.

At that event, Hernández-Ávila cited Samet’s scientific and professional achievements, among them his 27 books, 127 chapters and more than 350 scientific articles. “This Honoris Causa is awarded to recognize Dr. Samet’s work for global public health — for the health of all people,” he said.

A graduate of the University of Rochester School of Medicine and Dentistry, Samet has participated since the 1980s in the reports of the U.S. surgeon general on smoking and health, and he served as senior scientific editor for the 50-year anniversary edition in 2014. Most recently, he contributed to the 2016 surgeon general report on e-cigarettes and youth, the first of its kind.

His work has contributed to national legislation to control tobacco use, air pollution and radiation both in the United States and Mexico.

“I’m honored to be a part of this celebration to mark INSP’s decades-long commitment to public health in Mexico and to receive this very high recognition,” Samet said. “I look forward to continuing our partnership for many years to come.