Air Pollution Linked to Brain Tumor Risk

Study of 4 Million Danes Reveals Association with Meningioma

Long-term exposure to common air pollutants may increase the likelihood of developing meningioma, a tumor originating from the membranes surrounding the brain and spinal cord. This finding emerges from a large-scale Danish study, adding to evidence of air pollution’s detrimental effects beyond cardiovascular and respiratory systems.

Pollutants and Tumor Development

The comprehensive cohort study, which tracked nearly 4 million adults since 1991, identified a consistent link between increased meningioma risk and exposure to ultrafine particles (UFPs), fine particulate matter, nitrogen dioxide, and elemental carbon. These associations were observed even after accounting for various individual and area-level factors.

Study Methodology

Researchers utilized nationwide Danish registries to gather data on participants’ addresses and relevant covariates. Air pollution levels at residential locations were assessed using a validated model, with contributions from local traffic and other sources quantified through a national emission inventory. The study’s primary focus was the incidence of primary central nervous system (CNS) tumors, including meningiomas, gliomas, cranial nerve tumors, and other CNS tumors, as reported in the Danish Cancer Registry.

Key Findings on Tumor Types

Over 16,000 CNS tumors were identified in the study group. Meningiomas constituted 28% of these cases. For meningioma, a 10-year mean exposure to UFPs, fine particulate matter, nitrogen dioxide, and elemental carbon each showed an associated increased risk. Sensitivity analyses indicated that traffic-related UFPs had a stronger association compared to non-traffic UFPs, while both traffic and non-traffic fine particulate matter demonstrated similar risk increases. Notably, no clear links were found between air pollutants and glioma risk, although nitrogen dioxide showed a negative association with cranial nerve tumors.

Expert Commentary

“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.”

—Ulla A. Hvidtfeldt, PhD, Danish Cancer Institute

The findings highlight a significant public health concern, particularly given that ambient particulate matter pollution levels in many urban areas globally exceed World Health Organization guidelines. For instance, the average annual PM2.5 concentration in London was 10.3 µg/m³ in 2022, exceeding the WHO guideline of 5 µg/m³ (IQAir 2022).

Limitations and Future Research

The researchers acknowledged certain limitations, including a strong intercorrelation among pollutants and uncertainty in pollution estimates, which could affect the precise attribution of effects and personal exposure classification. Factors such as genetic predisposition, radiation exposure, and lifestyle variables were not fully accounted for, potentially leading to residual confounding. The study also noted potential biases from differential tumor detection and reliance on emission inventories of varying accuracy for distinguishing traffic from non-traffic pollution sources.