After following nearly 4m people over 21 years, Danish researchers have suggested that exposure to higher levels of air pollution over time was tied to a higher risk of meningioma, a type of brain tumour that is not usually cancerous but which can cause other health problems, reports Euronews.
Meningiomas are the most common type of primary brain tumour, and grow slowly enough that it can take years before they are detected. They originate in membranes that surround the brain and spinal cord.
Only rarely are they cancerous, but meningiomas can cause other disabilities by affecting nearby brain tissue, nerves, or vessels.
The researchers, from the Danish Cancer Institute, found that about 16 600 of the 4m adults they followed developed tumours of the central nervous system, including about 4 600 who developed meningioma.
The scientists then estimated their exposure levels to different types of air pollution, for example traffic emissions and diesel pollution, over a decade.
The analysis found people with more exposure to air pollution were at higher risk of meningioma – but there was not a strong link between air pollution and more aggressive brain tumours, such as gliomas.
The greatest risks were from ultrafine particles from exhaust, smoke and emissions.
The study does not prove that air pollution causes meningioma, only that there is a link between the two, they said. But it adds to the growing body of evidence that air pollution is bad for people’s health.
Other research has shown that ultra-fine particles can cross the blood-brain barrier and could harm brain tissue.
“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,” said Ulla Hvidtfeldt, one of the study’s authors and a senior scientist at the Danish Cancer Institute.
It shows that “air pollution can affect the brain, not just the heart and lungs”, Hvidtfeldt added.
The findings of the study – published in Neurology – also shed new light on meningiomas, given scientists do not know exactly what causes them. Other risks include radiation, particularly in childhood, and a genetic condition called Neurofibromatosis type 2.
The study has some limitations, notably that researchers estimated people’s air pollution exposure based on the outdoor air quality of their neighbourhoods. It did not include possible exposure to dirty air at work, or account for how much time they spent indoors.
“More research is needed to confirm these results, but if cleaning up our air can help lower the risk of brain tumours, that could make a real difference for public health,” Hvidtfeldt said.
Study details
Ambient Outdoor Air Pollution and Risk of Tumours of the Central Nervous System
Ulla Hvidtfeldt, Mette Sørensen, Aslak Poulsen et al.
Published in Neurology on 9 July 2025
Abstract
Background and Objectives
The incidence of CNS tumours has increased over the recent decades, and few risk factors are identified. Ultrafine particles (UFPs) can cross the blood-brain barrier and thereby cause direct intracranial exposure. The aim of this cohort study was to study the possible relationship between air pollution exposure including UFPs and tumours of the CNS.
Methods
The study base included all Danish adults (aged 20 years and older) identified from nationwide registries since 1991. We defined the end point as the first, primary CNS tumour identified in the Danish Cancer Registry. We applied Danish national registers for address histories and covariates and a state-of-the-art, validated model for assessment of residential air pollution. Cox proportional hazards models were used to estimate hazard ratios (HRs) with 95% CIs for tumours of the cranial nerves, meningioma, and glioma associated with air pollution exposure. We conducted analyses based on a national emission inventory to allocate air pollution concentrations to contributions from local traffic and other sources. Covariates included socioeconomic and demographic factors at both individual and area levels.
Results
The study included 3,959,619 adults (mean age 35 years, 49.6% female) and 16,596 cases of CNS tumours. Ten-year mean exposure to UFPs, fine particulate matter (PM2.5), nitrogen dioxide (NO2), and elemental carbon (EC) was associated with the risk of developing meningioma with confounder-adjusted HRs (95% CI) of 1.10 (1.05–1.16) per interquartile range (IQR) for UFPs; 1.21 (1.10, 1.34) per IQR for PM2.5; 1.12 (1.07, 1.18) per IQR for NO2; and 1.03 (1.00, 1.05) per IQR for EC. Source-specific analyses indicated that air pollution from both local traffic and other sources could be influential. Corresponding HRs observed for the other CNS groups were as follows: tumours of the cranial nerves (n = 2,342): 0.94 (0.86–1.02), 0.89 (0.76–1.03), 0.90 (0.83–0.97), and 0.92 (0.87–0.98); glioma (n = 6,197): 1.01 (0.96–1.06), 0.95 (0.87–1.04), 1.02 (0.97–1.06), and 1.01 (0.99–1.04); and other CNS tumours (n = 3,412): 0.96 (0.90–1.02), 0.89 (0.80–1.00), 0.99 (0.94–1.05), and 1.01 (0.98, 1.05).
Discussion
The findings of this nationwide register-based cohort study indicated that air pollution might contribute to the development of meningioma.
Neurology article – Ambient Outdoor Air Pollution and Risk of Tumours of the Central Nervous System
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