This story was originally published by The Guardian and appears here as part of the Climate Desk collaboration Fine-particulate air pollution can drive devastating forms of dementia by triggering the formation of toxic clumps of protein that destroy nerve cells as they spread through the brain, research suggests. Exposure to the airborne particles causes proteins in the brain to misfold into the clumps, which are hallmarks of Lewy body dementia, the third most common form of dementia after Alzheimer’s disease and vascular dementia. “The most direct implication is that clean air policies are brain health policies.” The researchers began by analyzing hospital records of the 56.5 million US Medicare patients. Armed with the patients’ zip codes, the scientists estimated their long-term exposure to PM2.5 pollution, airborne particles that are smaller than 2.5 thousandths of a millimetre. These can be inhaled deep into the lungs and are found in the bloodstream, brain and other organs.