Particulate Air Pollutants and Trajectories of Depressive Symptoms in Older Women

Objectives: Although several environmental factors contribute to the etiology of late-life depressive symptoms, the role of ambient air pollution has been understudied. Experimental data support the neurotoxicity of airborne particulate matter with aerodynamic diameter of ≤2.5 μm (PM2.5), but it remains unclear whether long-term exposure is associated with late-life depressive symptoms. Our secondary aim was to explore whether the observed associations between exposure and depressive symptoms are explained by dementia risk. Design, Setting, and Participants: Prospective community-dwelling cohort study from the Women's Health Initiative Study of Cognitive Aging (1999–2010). Our analyses included 1,989 older women (baseline age 73.3 ± 3.75) with no prior depression or cognitive impairment. Measurements: Participants completed annual assessments of depressive symptoms (15-item Geriatric Depression Scale). Average ambient PM2.5 exposure at the residential location was estimated by spatiotemporal modeling for the 3-years preceding each neuropsychological assessment. Participants underwent separate annual examinations for incident dementia defined by DSM-IV. Latent-class mixture models examined the association between PM2.5 and identified trajectories of symptoms. Results: Six trajectories of depressive symptoms were identified. Across all women, PM2.5 exposure was positively associated with depressive symptoms. The effect was especially strong in two clusters with sustained depressive symptoms (n = 625 sustained-mild [31%]; n = 125 sustained-moderate; [6%]). Among those with sustained-moderate symptoms, the estimated adverse effect of PM2.5 exposure was greater than that of hypertension. Among women without dementia, associations were modestly attenuated. Conclusion: Long-term exposure to ambient fine particles was associated with increased depressive symptoms among older women without prior depression or cognitive impairment