The Air We Breathe And The Hidden Danger Of Brain Tumors

The study followed nearly 4 million adults in Denmark to investigate whether air pollution is linked to the development of central nervous system tumors. The researchers calculated exposure to different pollutants in their home over a ten-year period and found an association between higher levels of pollution, especially ultrafine particles, PM2.5, and nitrogen dioxide, and a slightly increased risk of meningioma. There was no significant link with other types of brain tumors.

In recent decades, the number of people diagnosed with tumors of the central nervous system, which include structures such as the brain, spinal cord, and cranial nerves, has been increasing. Despite this, science still knows few clear risk factors to explain this increase.

A recent line of research suggests that extremely small particles present in air pollution, called ultrafine particles, can cross the natural barrier that protects the brain, the blood-brain barrier, and reach brain tissue directly.

This raises the hypothesis that prolonged exposure to air pollution may increase the risk of developing certain types of brain tumors. The objective of this research was precisely to investigate this possible relationship.

To conduct the study, researchers used data from virtually the entire adult population of Denmark aged 20 and over, registered in national databases since 1991. These records allowed them to track the health, residential history, and personal and socioeconomic information of the participants.

The focus was to identify new cases of primary central nervous system tumors—that is, tumors that originate in the brain tissue itself or associated structures and have not spread there from other parts of the body. Cases were identified through the Danish Cancer Registry, an official and comprehensive database.

One of the central points of the work was to estimate the amount of pollution to which each person was exposed in their home over a ten-year period. To do this, the scientists used a highly accurate and validated calculation model that takes into account actual measurements, weather patterns, vehicle and industrial emissions, and the exact location of the person's address.

This model allowed for the measurement of different types of pollutants, including ultrafine particles, fine suspended particles known as PM2.5, nitrogen dioxide, and elemental carbon. In addition to calculating the total amount of pollution, the study separated the contribution coming specifically from local traffic and other sources, such as industry and domestic heating.

The data were then analyzed using a statistical method called the Cox proportional hazards model. This type of analysis helps estimate whether people more exposed to certain pollutants have a higher likelihood of developing a specific type of tumor, taking into account other factors that could influence risk, such as age, sex, income, and characteristics of the region where they live.

Unlike a simple comparison of averages, this technique considers the time until the event (in this case, the tumor diagnosis) and adjusts the calculation to eliminate distortions caused by external factors.

In total, the study followed nearly four million adults, with an average age of 35 and a balanced ratio of men and women. During the period analyzed, more than 16,000 cases of central nervous system tumors occurred.

The results showed that prolonged exposure to pollution, especially to ultrafine particles, fine PM2.5 particles, and nitrogen dioxide, was associated with a slightly higher risk of developing meningiomas, which are generally benign tumors of the membranes covering the brain and spinal cord.

Meningioma

Interestingly, no significant association was observed between air pollution and other types of tumors, such as gliomas or cranial nerve tumors.

These findings suggest that, even if the increased risk is relatively small, widespread exposure to air pollution can have a significant impact on the number of meningioma cases. The research reinforces the importance of public policies that reduce pollutant emissions, especially in urban areas with heavy traffic.

READ MORE:

Ambient Outdoor Air Pollution and Risk of Tumors of the Central Nervous System

Ulla A. Hvidtfeldt, Mette Sørensen, Aslak H. Poulsen, Matthias Ketzel, Jørgen Brandt, Lau C. Thygesen, Jan Wohlfahrt, and Ole Raaschou-Nielsen

Neurology, Volume 105, Number 3, August 12, 2025

DOI: 10.1212/WNL.0000000000213920

Abstract: 

The incidence of CNS tumors 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 tumors of the CNS. 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 tumor 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 tumors 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. The study included 3,959,619 adults (mean age 35 years, 49.6% female) and 16,596 cases of CNS tumors. 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: tumors 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 tumors (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). The findings of this nationwide register-based cohort study indicated that air pollution might contribute to the development of meningioma.