The new study published in Nature journal Translational Psychiatry on Jan. 31 showed an association between tiny air pollutants and cognitive decline and dementia, a disorder of the mental processes marked by personality changes, memory disorders, and impaired reasoning.
Dangers Of Fine And Inhalable Particles Produced By Fossil Fuels
Study researcher Caleb Finch, from the University of Southern California's Leonard Davis School of Gerontology, explained that the microscopic particles produced by fossil fuels get into the body and into the brain through the nose. The cells in the brain treat these particles as invaders so they react with inflammatory responses, which exacerbate over the course of time and promote Alzheimer's disease.
The offending pollutants, the PM2.5, are fine and inhalable particles with 2.5 micrometer diameter or smaller. The human hair, which is about 70 micrometers in diameter, is 30 times bigger than the largest of these PM2.35 particles.
The findings back up earlier studies showing the dangers of air pollution on mental health. In a study published in January this year, researchers revealed that living in areas near high-traffic roads, where air pollution level is high due to the number of passing vehicles, is linked to 12 percent increased risk for dementia.
Air Pollutants And Dementia Risk In Older Women
The new study involved more than 3,000 women between 65 and 79 years old who initially did not have dementia.
By looking at the data of the 3,647 enrolled in the Women's Health Initiative Memory Study (WHIMS), researchers have found that older women who live in places where fine particulate matter exceeds the standard of the U.S. Environmental Protection agency have 81 percent increased likelihood of suffering from cognitive decline, and 92 percent increased odds for dementia.
"We hypothesized that long-term PM2.5 exposure increases the risk for accelerated global cognitive decline and dementia, further exacerbated by APOE ε4," Finch and colleagues wrote in their study. "These hypotheses were tested within the Women's Health Initiative Memory Study (WHIMS), a well-characterized, nationwide prospective cohort of older US women, for which we recently reported associations between elevated PM2.5 and smaller white matter volumes in multiple brain regions."
Stronger Risk For Carriers Of APOE4 Gene
Experiments with laboratory mice also showed that the adverse effect of the pollutant was stronger in women with APOE4 gene, a genetic variation associated with increased odds for Alzheimer's disease.
Researchers chronically exposed female mice with the APOE4 gene to nano-sized air pollution over a period of 15 weeks. Researchers found that these mice accumulated up to 60 percent more of the amyloid plaque that boosts progress of Alzheimer's than mice that do not have the APOE4 gene.
"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," said Jiu-Chiuan Chen, from the Keck School of Medicine of USC.