Air pollution linked to higher risk of developing Alzheimer's disease

People with greater exposure to air pollution face a higher risk of developing Alzheimer's disease, according to a new study by Yanling Deng of Emory University, U.S.A., and colleagues, published February 17^th in the open-access journal PLOS Medicine.

Alzheimer's disease is the most common form of dementia, affecting about 57 million people worldwide. Exposure to air pollution is a known risk factor for Alzheimer's disease, and for several common chronic health conditions, such as hypertension, stroke and depression. These chronic conditions are also linked to Alzheimer's disease, but previously it was unclear whether air pollution causes these chronic conditions, which then lead to dementia, or if these conditions might amplify the effects of air pollution on brain health.

A team at Emory University studied more than 27.8 million U.S. Medicare recipients aged 65 years and older from 2000 to 2018. The researchers looked at individuals' air pollution exposure level and whether they developed Alzheimer's disease, while emphasizing the role of other chronic conditions. They found that greater exposure to air pollution was associated with an increased risk of Alzheimer's disease, and that association was slightly stronger in individuals who had experienced a stroke. Hypertension and depression, however, had little additional impact.

Overall, the findings suggest that air pollution contributes to Alzheimer's disease mostly through direct pathways rather than through other chronic health conditions. However, people with a history of stroke may be especially susceptible to the harmful effects of air pollution on brain health. The study indicates that improving air quality could be an important way to prevent dementia and protect older adults.

The authors add, "In this large national study of older adults, we found that long-term exposure to fine particulate air pollution was associated with a higher risk of Alzheimer's disease, largely through direct effects on the brain rather than through common chronic conditions such as hypertension, stroke, or depression."

"Our findings suggest that individuals with a history of stroke may be particularly vulnerable to the harmful effects of air pollution on brain health, highlighting an important intersection between environmental and vascular risk factors."