A major new study of more than 27.8 million older adults in the United States has found that long-term exposure to air pollution is linked to a higher risk of developing Alzheimer’s disease. The research, published in the medical journal Public Library of Science Medicine, suggests that polluted air may directly harm the brain, not just worsen other health conditions associated with dementia.

Researchers analyzed data from adults aged 65 and older between 2000 and 2018, comparing levels of air pollution exposure with new Alzheimer’s diagnoses. They found a consistent pattern: the greater the exposure to polluted air, the higher the risk of the disease. The link was especially strong among people who had previously experienced a stroke, while conditions such as high blood pressure and depression did not significantly intensify the effect.

Scientists believe tiny airborne particles can enter the lungs, pass into the bloodstream, and reach the brain. Once there, they may trigger inflammation, damage blood vessels, and accelerate the buildup of harmful proteins associated with Alzheimer’s. The findings suggest that improving air quality could play a significant role in reducing dementia risk, making pollution control not only an environmental priority but also a major public health concern.