Air pollution may lead to dementia in older women

Tiny particles that pollute the air — the kind that come mainly from power plants and automobiles — may greatly increase the chance of dementia, including dementia caused by Alzheimer’s disease, according to research co-led by Caleb Finch of biological sciences at USC Dornsife.

Scientists and engineers found that older women who live in places with fine particulate matter exceeding the United States Environmental Protection Agency’s (EPA) standard are 81 percent more at risk for global cognitive decline and 92 percent more likely to develop dementia, including Alzheimer’s.

If their findings hold up in the general population, air pollution could be responsible for about 21 percent of dementia cases, according to the study.

“Microscopic particles generated by fossil fuels get into our body directly through the nose into the brain,” saidFinch, co-senior author of the study. Finch is University Professor, professor of gerontology at the USC Leonard Davis School of Gerontology, and professor of biological sciences, anthropology and psychology at USC Dornsife.

“Cells in the brain treat these particles as invaders and react with inflammatory responses, which over the course of time, appear to exacerbate and promote Alzheimer’s disease,” he said. “Although the link between air pollution and Alzheimer’s disease is a new scientific frontier, we now have evidence that air pollution, like tobacco, is dangerous to the aging brain.”

According to University Professor Caleb Finch, microscopic particles generated by fossil fuels get into our body and directly through the nose into the brain. Animation by Meg Rosenburg.

The adverse effects were stronger in women who had the APOE4 gene, a genetic variation that increases the risk for Alzheimer’s.

“Our study — the first of its kind conducted in the U.S. — provides the inaugural scientific evidence of a critical Alzheimer’s risk gene possibly interacting with air particles to accelerate brain aging,” said Jiu-Chiuan Chen, co-senior author of the study and an associate professor of preventive medicine at the Keck School of Medicine of USC. “The experimental data showed that exposure of mice to air particles collected on the edge of USC damaged neurons in the hippocampus, the memory center that is vulnerable to both brain aging and Alzheimer’s disease.”

Published earlier this year in the Nature journal Translational Psychiatry, the study adds to an emerging body of research from around the world that links air pollution to dementia. The offending pollutants, known as PM2.5, are fine particles with diameters 2.5 micrometers or smaller. Resting side by side, more than 30 would fit across the width of a human hair.

Combining human data and lab experiments

The researchers analyzed data of more than 3,600 women age 65 to 79 from the Women’s Health Initiative Memory Study (WHIMS). The WHIMS participants lived across 48 states and did not have dementia when they enrolled.

Using technology invented by Constantinos Sioutas, Fred Champion Professor of Civil and Environmental Engineering at USC Viterbi and a co-author of the study, USC scientists exposed female mice carrying the APOE4 gene to nano-sized air pollution for 15 weeks.

“Our state-of-the-art aerosol technologies, called particle concentrators, essentially take the air of a typical urban area and convert it to the air of a freeway or a heavily polluted city like Beijing,” Sioutas said, “We then use these samples to test exposure and assess adverse neuro-developmental or neurodegenerative health effects.”

They found that mice predisposed to Alzheimer’s disease accumulated as much as 60 percent more amyloid plaque, the toxic clusters of protein fragments that further the progression of Alzheimer’s, than normal mice.

University Professor Caleb Finch. Photo courtesy of USC Davis School of Gerontology.

A global health issue

Worldwide, nearly 48 million people suffer from dementia, and there are 7.7 million new cases every year, according to the World Health Organization.

“Our study has global implications, as pollution knows no borders,” said Finch, holder of the ARCO/William F. Kieschnick Chair in the Neurobiology of Aging.

USC researchers and others in this field said more research is needed to confirm a causal relationship and to understand how air pollution enters and harms the brain. Accurate pollution monitors are important for this task.

Less than one-third of all counties in the United States have ozone or particle pollution monitors, according to the American Lung Association. Ambient monitoring data from the EPA are critical for scientists conducting research on air pollution and public health, Chen said.

“We analyzed data of high PM2.5 levels using standards the EPA set in 2012,” Chen said. “We don’t know whether the lower PM2.5 levels of recent years have provided a safe margin for older Americans, especially those at risk for dementia.”

Six of the top 10 cities in the nation most polluted by PM2.5 are in California, including Los Angeles, Long Beach and Fresno, according to the American Lung Association. Yet, certain areas have seen cleaner air in recent decades. Reducing PM2.5 in the air we breathe coincides with fewer cases of dementia, the researchers pointed out, referencing the data of others.

The insidious effects of PM2.5

“Many studies have suggested that early life adversities may carry into later life and affect brain aging,” Chen said. “If this is true, then maybe long-term exposure to air pollution that starts a downward spiral of neurodegenerative change in the brain could begin much earlier and rev up in later life.”

In other studies, Chen and his colleagues linked long-term exposure to high PM2.5 levels to smaller volumes of key brain matter in important areas such as the frontal lobe, which carries out thinking, decision making and planning.

The new study examined only women and female mice. Future studies will include both sexes to evaluate generalizability to men and will also explore how PM2.5 interacts with cigarettes and other pollutants.

The air pollution study, the Women’s Health Initiative and WHIMS are collectively supported by the National Institute on Aging of the National Institutes of Health; the Southern California Environmental Health Sciences Center funded by the National Institute of Environmental Health Sciences; the National Heart, Lung, and Blood Institute; the U.S. Department of Health and Human Services; Wyeth Pharmaceuticals Inc.; St. Davids, PA, and the Wake Forest School of Medicine; and the Cure Alzheimer’s Fund.