Breathing polluted air may increase risk of widespread brain tumor

People exposed to higher levels of air pollution may have an increased risk of developing meningioma, a typically benign brain tumor, according to a large study published in Neurology. This common type of tumor forms in the membranes that cover the brain and spinal cord. The results don’t prove that air pollution causes meningioma; they just show a link between the two.

The study analyzed several types of air pollutants, including those commonly associated with motor vehicle traffic, such as nitrogen dioxide and ultrafine particles, which are particularly concentrated in urban areas.

"Various types of air pollution have already been shown to have negative health effects, and ultrafine particles are small enough to penetrate the blood-brain barrier and can 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 transport and other sources may play a role in the development of meningioma and adds to growing evidence that air pollution affects not only the heart and lungs but also the brain."

The study included nearly 4 million Danish adults with an average age of 35 and followed them for 21 years. During that time, 16,596 people were diagnosed with a central nervous system tumor, including 4,645 cases of meningioma.

Scientists used residential data and advanced models to estimate the long-term impact of air pollution.

They calculated the average 10-year exposure to the following pollutants:

• ultrafine particles less than 0.1 micrometers in diameter;
• fine particulate matter (PM2.5) measuring 2.5 micrometers or less;
• nitrogen dioxide (NO₂), a gas produced primarily by automobile exhaust;
• elemental carbon, a marker of pollution from diesel engines.

The researchers then compared people with the lowest and highest exposure levels, dividing them into three groups for each pollutant.

For example, for ultrafine particles, people with the lowest exposure had a 10-year mean of 11,041 particles/cm³, while those with the highest had a mean of 21,715 particles/cm³. In these groups, meningioma developed in 0.06% of people with low exposure and 0.20% of people with high exposure.

After adjusting for factors such as age, gender, education level, and the socioeconomic status of the area where they lived, the researchers found that people with higher levels of exposure to pollutants had a higher risk of developing meningioma:

• 10% higher risk for ultrafine particles with an increase of 5,747 particles/cm³;
• 21% higher risk for fine particulate matter with an increase of 4.0 µg/m³;
• 12% higher risk for nitrogen dioxide with an increase of 8.3 µg/m³;
• 3% higher risk for elemental carbon per 0.4 µg/m³ increase.

The study found no strong link between these pollutants and more aggressive brain tumors such as gliomas.

“While research into the health effects of ultrafine particles is still in its early stages, these data suggest a possible link between exposure to transport-related ultrafine particles and the development of meningioma,” Hvidtfeldt said.
“More research is needed to confirm these findings, but if cleaning the air helps reduce the risk of brain tumours, it could have a real impact on public health.”

A limitation of the study is that pollution levels were measured based on outdoor air quality near participants' homes and did not take into account all sources of individual exposure, such as workplace air or time spent indoors.