Association between environmental air pollution and olfactory functioning among Italian adolescents and young adults in the province of Brescia, Italy

Olfactory receptor neurons are in direct contact with the ambient air, making olfactory function particularly susceptible to airborne pollutants. This study investigates the relationship between air pollution and olfactory function among adolescents and young adults residing in the province of Brescia, Italy. It included 169 participants (53.3% female, 15-25 years) of the ongoing longitudinal Public Health Impact of Metals Exposure (PHIME) study. Participants completed assessments of olfactory function using a short version of the "Sniffin' Sticks" identification test at baseline (2008-2014) and the extended test at follow-up (2017-2021). Annual average concentrations of particulate matter (PM10, PM2.5) and nitrogen dioxide (NO2) were estimated on a 4 x 4 km2 spatial resolution grid using the Regional Chemical Transport Model ARIA for the target area between 2016 and 2019 and averaged over time. We applied multivariable linear regression, Bayesian Kernel Machine Regression and Weighted Quantile Sum (WQS) regression to investigate the associations between air pollutants and olfactory function. A significant negative association was observed between the air pollutants (PM2.5: mean 18.5 mu g/m3 Standard Deviation +5.2 mu g/m3; PMCOARSE: 2.7 mu g/m3 +1.2 mu g/m3; NO2: 32.3 mu g/m3 +10.1 mu g/m3), treated as a mixture, and the olfactory functioning measured with the Sniffin' total score (mu -1.44, 95%CI -2.42, -0.34), and the Sniffin' threshold score (mu -1.48, 95%CI -2.91, -0.6) when applying WQS regression. This association was mainly driven by NO2 and PMCOARSE. Findings suggest that air pollution exposure to NO2 and PMCOARSE, can reduce olfactory function among adolescents and young adults residing in a polluted area in northern Italy.