Mental Health
Longitudinal associations between environmental mixtures and depressive symptoms in older adults: the Reasons for Geographical and Racial Differences in Stroke (REGARDS) study Jeroen van Baar* Jeroen van Baar van Baar van Baar van Baar van Baar van Baar van Baar van Baar van Baar van Baar Boston University School of Public Health
Depressive symptoms are common in older age, but their environmental determinants are poorly understood. We assessed the relationship between multiple environmental exposures and depressive symptoms in 21,949 Black and white older Americans in the longitudinal Reasons for Geographic and Racial Differences in Stroke (REGARDS) study (mean age = 64.3 ± 8.9 (s.d.) yrs at baseline, 2003-2007). We linked data on air pollution (PM2.5, NO2, O3), anthropogenic noise, neighborhood socioeconomic status (nSES), and neighborhood segregation (Income index of concentration at the extremes [ICE], Race ICE, Race-Income ICE) to subjects’ time-varying addresses (2005-2016). Depressive symptoms were measured 1-5 times per subject using the 4-item Center for Epidemiologic Studies Depression scale (CESD4; 2008-2016). We first analyzed each exposure independently, regressing CESD4 onto the cumulative mean exposure since baseline in zero-inflated Poisson models adjusted for antidepressant use, demographics, and individual SES. NO2 (IRR = 1.02 per one-quartile increase, 95% CI = [1.00–1.04]) and anthropogenic noise (IRR = 1.02 [1.00–1.04]) predicted more depressive symptoms; nSES (IRR = 0.97 [0.95–0.99]) and the three ICEs (IRRs between 0.95 [0.93–0.97] and 0.96 [0.94–0.97]) predicted fewer symptoms. We then modeled the mixture of all cumulative exposures using quantile g-computation, adjusting for the same covariates. Greater mixture exposure predicted more depressive symptoms (IRR = 1.08 [1.05–1.10] per quartile increase in all exposures at the same time). The strongest mixture contributors were income ICE (weight = -0.54) and NO2 (weight = 0.51). In stratified analyses, Race ICE and Race-Income ICE contributed to more depressive symptoms in Black participants but fewer in white participants. These findings suggest that multiple exposures jointly contribute to depressive symptom risk in later life and motivate further research on potential racial differences in environmental risk factors.