Breathing dirty air? It may raise the risk of a common brain tumor

People exposed to higher levels of air pollution may be more likely to develop meningioma, a typically noncancerous brain tumor, according to a large study published July 9, 2025, in Neurology®Clinical Practice, an official journal of the American Academy of Neurology. This common type of brain tumor forms in the lining of the brain and spinal cord. The findings do not prove that air pollution causes meningioma; they only show a link between the two.

The study analyzed several air pollutants, including those commonly linked to traffic-such as nitrogen dioxide and ultrafine particles-which are especially concentrated in urban environments.

“Various types of air pollution have been shown to have negative effects on health, and ultrafine particles are small enough to cross the blood-brain barrier and may directly affect brain tissue,’ said study author Ulla Hvidtfeldt, PhD, of the Danish Cancer Institute in Copenhagen. “Our study suggests that long-term exposure to air pollution from traffic and other sources may play a role in the development of meningioma and adds to the growing body of evidence that air pollution can affect the brain-not just the heart and lungs.”

The study included nearly 4 million adults in Denmark with an average age of 35 who were followed over a 21-year period. During that time, 16,596 people developed a tumor of the central nervous system, including 4,645 who developed meningioma.

Researchers used address histories and advanced modeling to estimate long-term exposure to air pollution.

They calculated 10-year average exposure to the following: ultrafine particles with particles less than 0.1 micrometers in diameter; fine particulate matter, also called PM2.5, with particles that are 2.5 micrometers in diameter or less; nitrogen dioxide, a gas mostly from traffic emissions; and elemental carbon, a marker of diesel pollution.

Researchers then compared people with the lowest exposure to those with the highest by dividing people into three groups for each pollutant.

For example, for ultrafine particles, people in the lowest group had an average 10-year exposure of 11,041 particles per centimeter cubed (cm3) compared to people with the highest exposure of 21,715 particles/cm3. In these groups, 0.06% of people in the group with the lowest exposure developed meningiomas compared to 0.20% of people with the highest exposure.

After adjusting for factors like age, sex, education level and neighborhood socioeconomic status, researchers found that people with higher exposure to air pollutants had a greater risk of developing meningioma:

• 10% higher risk for ultrafine particles for every increase of 5,747 particles/cm3

• 21% higher risk for fine particulate matter for every increase of 4.0 micrograms per meter cubed (µg/m3)

• 12% higher risk for nitrogen dioxide for every 8.3 µg/m3

• 3% higher risk for elemental carbon for every 0.4 µg/m3

The study did not find strong links between these pollutants and more aggressive brain tumors, such as gliomas.

“While research on the health effects of ultrafine particles is still in its early stages, these findings point to a possible link between traffic-related ultrafine particle exposure and the development of meningioma,” Hvidtfeldt said. “More research is needed to confirm these results, but if cleaning up our air can help lower the risk of brain tumors, that could make a real difference for public health.”

A limitation of the study is that pollution exposure was based on outdoor air quality near people’s homes, so it doesn’t capture all sources of personal exposure-like workplace air or time spent indoors.

Reference:

Ulla A. Hvidtfeldt, Ambient Outdoor Air Pollution and Risk of Tumors of the Central Nervous System, Neurology, https://doi.org/10.1212/WNL.0000000000213920.