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

Abstract

BACKGROUND AND OBJECTIVES 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. 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 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. RESULTS 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). DISCUSSION The findings of this nationwide register-based cohort study indicated that air pollution might contribute to the development of meningioma.