This is how air pollution increases the risk of dementia.

There is growing evidence linking environmental factors to some dementias because they cause harmful changes in brain proteins that lead to neurodegeneration.

One of these diseases is Lewy body dementia, a group of neurodegenerative disorders characterized by the abnormal accumulation of the protein alpha-synuclein in the brain.

Now, research published in the journal Science shows that exposing mice to fine particulate matter (PM2.5) from industrial activity, residential burning, wildfires and vehicle emissions triggered the formation of abnormal clumps of alpha-synuclein. These toxic clumps shared key structural and pathological features with those found in human brains with Lewy body dementia, said lead researcher Xiaobo Mao of Johns Hopkins University .

The research began by analyzing hospital data from 56.5 million patients in the U.S. admitted between 2000 and 2014 with neurodegenerative diseases. The team focused on newly hospitalized patients with Lewy body-related pathologies and estimated their long-term exposure to PM2.5 based on ZIP code. They found that an increase in PM2.5 pollution was associated with a 17% increased risk of Parkinson's dementia and a 12% increased risk of Lewy body dementia.

"The statistical association we found is even stronger than that observed in previous studies that group Alzheimer's with other dementias," said Xiao Wu, co-senior author of the study and a professor at the Columbia University Mailman School of Public Health . "This underscores that Lewy body formation could be a key pathway worthy of further biological investigation."

To investigate the link between pollution and Lewy body dementia, Mao's team exposed normal and genetically modified mice to PM2.5 particles for several months. The normal mice showed brain damage and cognitive decline, while those that didn't produce alpha-synuclein showed no effects. In mice with a human mutation linked to Parkinson 's , exposure led to abnormal accumulations of alpha-synuclein and memory loss. Moreover, the effects were similar using polluting particles from different regions (China, Europe, and the U.S.), suggesting that the harms of PM2.5 may be global.

The researchers also observed that changes in gene expression in the brains of mice exposed to PM2.5 were strikingly similar to those found in human patients with Lewy body dementia.

"This indicates that pollution could not only trigger the accumulation of toxic proteins, but also alter the expression of disease-related genes in the human brain ," the researchers add.

Although genetic factors play an important role in neurodegenerative diseases, researchers point out that people can control their exposure to pollution to some extent.

The next goal is to identify the specific components of air pollution that cause these effects. "Understanding this could help guide public health efforts to reduce harmful exposures and lower the risk of these diseases," they conclude.