What do air pollution and Alzheimer’s disease have to do with each other?

From heart health to a sedentary lifestyle, researchers have identified a number of risk factors for dementia. Now, a new study examines air pollution as yet another potential risk factor.

To date, scientists have suspected a relationship between air pollution and Alzheimer’s disease, but the link has remained unclear. So, a group of researchers from several London universities sought a more definitive answer, according to Medical News Today.

The researchers first estimated noise and air pollution levels throughout Greater London in the United Kingdom. They then studied the 2004 medical records of nearly 131,000 people between the ages of 50 and 79. No participants included had diagnosed dementia. The Clinical Practice Research Datalink, a nonprofit research organization, provided the data.

Based on the participants’ addresses, the researchers estimated their individual exposure to various pollutants, including traffic noise. The pollutants of note included:

– Nitrogen dioxide (NO2)

– Fine particulate matter (PM2.5)

– Ozone (O3)

From there, the researchers tracked each participants’ health for an average of 7 years. Of the participant sample, 2,181 people (or 1.7%) developed dementia.

However, the analysis shows a 40% greater risk of a dementia diagnosis when exposed to greater levels of NO2. There was a similar relationship between a dementia diagnosis and high levels of PM2.5, according to the study.

On the other hand, O3 and noise pollution did not increase dementia risk, the study noted.

The observational nature of the study means there is no firm conclusion. The findings may only be relevant for the city of London, for instance, or other factors may have driven dementia diagnoses. Alzheimer’s and other dementias may take years to develop, too, so longer studies may be needed for a more concrete answer.

Still, if air pollution and Alzheimer’s disease are connected, how does air pollution affect the brain? Of many potential ways, the study’s authors outlined one example.

“Traffic-related air pollution has been linked to poorer cognitive development in young children, and continued significant exposure may produce neuroinflammation and altered brain innate immune responses in early adulthood,” the authors wrote.

In any case, reducing air pollution will prove beneficial for general public health. If it brings down the dementia risk, then all the better.

“Because air pollution already causes substantial health problems, lowering levels would be of great benefit to the public; it might also bring down dementia risk,” Medical News Today wrote. “Even if the reduction in risk is minimal, because dementia is so prevalent, it could make a huge difference.”