Can bad air quality affect your memory?

Here’s some good news for Earth Day: Particle pollution in hazy air from cars and factories has decreased significantly in the past 10 years. But you may want to hold your applause. Researchers have discovered this type of pollution causes higher rates of dementia and Alzheimer's disease.

In a recent article published in the journal Translational Psychiatry, medical experts analyzed health data collected between 1999 and 2010 from 3,647 women. The women ranged in age 65 to 79. None of them had dementia when they were enrolled in the study.

Women living in areas with “fine particle air pollution” above federal health standards for an average of more than three years were almost twice as likely to develop dementia, according to the study.

"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," said Caleb Finch, Ph.D., a professor at University of Southern California in Los Angeles and a co-author of the study.

Women exposed to high levels of particle pollution were 81 percent more at risk of total cognitive decline. Women exposed to high levels of particle pollution in combination with a genetic predisposition for Alzheimer’s disease face the greatest risk, the study suggests.

The researchers took these findings a step further by suggesting how particle pollution may help cause Alzheimer's disease. In studies on mice, they determined the particles "trigger" the development of amyloid plaque, a key symptom associated with Alzheimer’s.

More research needed

Additional research is required to understand how fine particle air pollution—known as PM2.5—enters and harms the brain. PM2.5 are inhalable molecules 30 times smaller than the diameter of a human hair and can only be seen with an electron microscope.

According to the Environmental Protection Agency, fine particle pollution is produced from all types of combustion, including motor vehicles, power plants, residential wood burning, forest fires and agricultural burning, for instance.

In addition to PM2.5, the EPA calculates air quality based on four major air pollutants: ground-level ozone, carbon monoxide, sulfur dioxide and nitrogen dioxide. For each of these pollutants, the EPA has established national air quality standards to protect public health. Ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health in the United States.

Six of the top 10 most polluted cities in the nation by PM2.5 are in California. The cities include Los Angeles, Long Beach and Fresno. Less than one-third of all counties in the United States have ozone or particle pollution monitors, according to the American Lung Association.

To check the air quality in your area by ZIP code, visit the American Lung Association's State of the Air website.

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