1632

Background: Bipolar Disorder (BD) alternates depressive, manic or hypomanic phases. A manic episode (ME) is the main psychopathological condition of BD and it often requires hospitalization. Air pollution is thought to play a role in onset and exacerbation of several psychiatric disorders. We thus aimed to verify the association between exposure to particulate matter ≤10µm (PM10) and ME severity, assessed through the Young Mania Rating Scale (YMRS). Methods: We evaluated clinical records regarding 414 hospital admissions of 186 patients residing in Milan (Italy), hospitalized for ME in the Psychiatry Unit of the Policlinico Hospital from 2007 to 2019. Patients were assigned mean daily PM10 and apparent temperature levels of the city of Milan. Different exposure windows were considered: single days preceding hospitalization (lag 0 to 15) and their average estimates (lag 0-1 to 0-15). We applied mixed effect models, adjusted for age at hospitalization/onset, sex, smoking habit, number of cigarettes per day, year of hospitalization, season, and apparent temperature. Results: Short-term PM10 exposure was associated with a reduction in YMRS, both when considering daily lags [β: -0.46 (95% Confidence Interval: -0.87; -0.06) at lag0] and their average [-0.50 (-0.94; -0.07) at lag0-1]. YMRS was higher in psychotic patients (24.7 vs. 16.6, p < 0.001) and lower when considering ME with vs. without mixed components (18.2 vs. 21.2, p < 0.001). Interestingly, while PM10 did not influence the risk of patients being psychotic at admission, it was associated with a 34% increased risk of having a ME with mixed features (i.e. with dysphoric and/or depressive symptoms) at lag0-1 [Odds Ratio: 1.34 (1.01; 1.78)]. Conclusions: Our findings show that PM10 exposure moves the ME towards the depressive pole of the BD spectrum and increases the probability of hospitalization for ME with mixed components.