Air pollution is associated with an increased risk of developing dementia, according to a new study.
Fine particles in the air can contribute to devastating forms of the disease, the research suggests, by propagating toxic clumps of protein in the brain.
Exposure to airborne particles makes it more likely to misfold into clumps, which can then destroy nerve cells in the brain. This is a common cause of Lewy body dementia, which researchers describe as a “devastating and increasingly prevalent neurodegenerative disorder”.
It is the second most common form of the disease after Alzheimer’s.
In light of the findings, scientists have called for a concerted effort to improve air quality by cutting emissions, improving wildlife management, and reducing wood burning in homes.
Dr Xiaobo Mao, neurologist at Johns Hopkins University and lead investigator of the study, said: “Unlike age or genetics, this is something we can change.”
“The most direct implication is that clean air policies are brain health policies,” he told The Guardian.
To draw their findings, researchers first analysed the hospital records of 56.5 million US Medicare patients, looking at those who were admitted between 2000 and 2014 with protein damage. By cross-referencing the symptom with the patients’ zip codes, they were able to estimate their long-term exposure to PM2.5 pollution – airborne particles smaller than 2.5 thousandths of a millimetre.
They theorised that long-term exposure to the particles, which can be inhaled into the lungs, raised the risk of Lewy body dementia.
Lewy bodies refer to the abnormal clumps that lead to the disease, which are made from a protein called alpha-synuclein. While the protein is essential for regulating brain function, it can misfold, meaning it assumes the wrong structure and is harmful.
They can kill nerve cells and cause diseases by spreading through the brain.
To confirm their findings, researchers tested their theory on mice by exposing them to PM2.5 pollution every other day for ten months. Some were normal mice, while others were genetically modified to prevent them from producing alpha-synuclein.
The experiment saw nerve cells die off in the normal mice, leading to brain shrinkage and cognitive decline. Meanwhile, the genetically modified mice showed little change.
Further research on mice showed that PM2.5 pollution was driving the formation of toxic clumps of alpha-synuclein that bore a resemblance to Lewy bodies in humans. These findings are considered compelling evidence despite being confirmed in mice.
“Our findings have profound implications for prevention because they identify air pollution as a modifiable risk factor for Lewy body dementia,” said Dr Mao.
“By lowering our collective exposure to air pollution, we can potentially reduce the risk of developing these devastating neurodegenerative conditions on a population-wide scale.”
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