Heterogenous air pollution exposure effects on the dynamic association between depressive symptoms and episodic memory in women aged 80 and older

Abstract

Background/aim: Elucidating how exposure influences interrelationships between episodic memory (EM) and depressive symptoms (DS) helps understand air pollution neurotoxicity on aging brain. Previously, in women primarily aged 70-years old (PMID:31881430), we showed PM2.5 (particulate matter <2.5 μm) may indirectly contribute to increased DS mediated by EM declines, but no indirect associations between exposure and decreased EM mediated by increased DS were found. How exposure was associated with such longitudinal interrelationship has not been examined in women aged ≥ 80, despite observed increased incidence with possibly different etiologies of these syndromes.Methods: Women aged ≥80 years at study baseline (N=1,430;age=83.80± 2.74 years), enrolled in the Women’s Health Initiative Memory Study-Epidemiology of Cognitive Health Outcomes, completed up to 5-annual assessments of EM (latent composite of East Boston Memory Test and Telephone Interview for Cognitive Status) and DS (15-item Geriatric Depression Scale). We estimated 3-year average exposures to regional PM2.5 and NO2 (proxy of traffic pollutants) both at baseline and during the remote period 10 years earlier, using regionalized national universal kriging. Latent-change structural equation models examined how exposures were associated with the interrelationship of annual changes in T-score standardized EM and DS while adjusting for covariates.Results: A statistically significant indirect effect of remote (p<0.05), but not recent (p>0.05), NO2 exposure on EM decline (β=-0.042, per interquartile=9.32ppb) mediated by increased DS was present. Remote NO2 was associated with increased DS (β=.270) which was associated with EM decline (β=-.155). PM2.5 exposure, remote or recent, was not indirectly associated with declines in EM. Regardless of exposure time period, no significant indirect effects of PM2.5 or NO2 on increases in DS mediated by EM were found.Conclusions: The adverse effect air pollution on the interplay between DS and EM of older women is heterogenous, likely varying by pollutants, exposure time period, and age.