Study warns breathing pollution increases risk of brain tumor

By Stephen Beech

Breathing dirty air can raise the risk of a brain tumor, warns new research.

People exposed to higher levels of air pollution may be more likely to develop meningioma - a usually non-cancerous brain tumor, say scientists.

The common type of brain tumor forms in the lining of the brain and spinal cord.

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

They say their findings, published in the journal Neurology, do not prove that air pollution causes meningioma; rather, they only show a link between the two.

But the team says the study suggests that cleaner air could help reduce the risk of brain tumors.

Study author Dr. Ulla Hvidtfeldt, of the Danish Cancer Institute, said: “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.

“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 four million adults in Denmark with an average age of 35 who were followed for 21 years.

During that period, 16,596 people developed a tumor of the central nervous system, including 4,645 who developed meningioma.

The research team used address histories and advanced modelling to estimate long-term exposure to air pollution.

They calculated 10-year average exposure to 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; plus elemental carbon, a marker of diesel pollution.

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

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 those groups, 0.06% of people in the group with the lowest exposure developed meningiomas compared to 0.2% of people with the highest exposure.

After adjusting for factors such as age, sex and education level, researchers found that people with higher exposure to air pollutants had a greater risk of developing meningioma.

The findings showed that there was a 10% higher risk for ultrafine particles for every increase of 5,747 particles/cm3, and a 21% higher risk for fine particulate matter for every increase of 4.0 micrograms per meter cubed.

The study did not find strong links between the pollutants and more aggressive brain tumors, including gliomas.

Dr. Hvidtfeldt said: “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."

She added: “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.”