Ambient Air Pollution and Long-Term Trajectories of Episodic Memory Decline among Older Women in the WHIMS-ECHO Cohort

Abstract

Background:

Episodic memory decline varies by age and underlying neuropathology. Whether ambient air pollution contributes to the heterogeneity of episodic memory decline in older populations remains unclear.

Objectives:

We estimated associations between air pollution exposures and episodic memory decline according to pollutant, exposure time window, age, and latent class subgroups defined by episodic memory trajectories.

Methods:

Participants were from the Women’s Health Initiative Memory Study–Epidemiology of Cognitive Health Outcomes. Older women ( $n=\mathrm{2,056}$ ; 74–92 years of age) completed annual (2008–2018) episodic memory assessments using the telephone-based California Verbal Learning Test (CVLT). We estimated 3-y average fine particulate matter [PM with an aerodynamic diameter of $\le 2.5\mathrm{\mu }\mathrm{m}$ ( ${\mathrm{PM}}_{2.5}$ )] and nitrogen dioxide ( ${\mathrm{NO}}_2$ ) exposures at baseline and 10 y earlier (recent and remote exposures, respectively), using regionalized national universal kriging. Separate latent class mixed models were used to estimate associations between interquartile range increases in exposures and CVLT trajectories in women $\le 80$ and $>80\text{\hspace{0.17em}years of age}$ , adjusting for covariates.

Results:

Two latent classes were identified for women $\le 80\text{\hspace{0.17em}years of age}$ ( $n=828$ ), “slow-decliners” { $\mathrm{slope}=-0.12/\mathrm{y}$ [95% confidence interval (CI): $-0.23$ , $-0.01$ ] and “fast-decliners” [ $\text{slope}=-1.79/\mathrm{y}$ (95% CI: $-2.08$ , $-1.50$ )]}. In the slow-decliner class, but not the fast-decliner class, ${\mathrm{PM}}_{2.5}$ exposures were associated with a greater decline in CVLT scores over time, with a stronger association for recent vs. remote exposures [ $-0.16/\mathrm{y}$ (95% CI: $-2.08$ , $-0.03$ ) per $2.88{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ and $-0.11/\mathrm{y}$ (95% CI: $-0.22$ , 0.01) per $3.27{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$ , respectively]. Among women $\ge 80\text{\hspace{0.17em}years of age}$ ( $n=\mathrm{1,128}$ ), the largest latent class comprised “steady-decliners” [ $\text{slope}=-1.35/\mathrm{y}$ (95% CI: $-1.53$ , $-1.17$ )], whereas the second class, “cognitively resilient”, had no decline in CVLT on average. ${\mathrm{PM}}_{2.5}$ was not associated with episodic memory decline in either class. A $6.25\text{-ppb}$ increase in recent ${\mathrm{NO}}_2$ was associated with nonsignificant acceleration of episodic memory decline in the $\le 80$ -y-old fast-decliner class [ $-0.21/\mathrm{y}$ (95% CI: $-0.45$ , 0.04)], and in the $>80\text{-y-old}$ cognitively resilient class [ $-0.10/\mathrm{y}$ (95% CI: $-0.24$ , 0.03)] and steady-decliner class [ $-0.11/\mathrm{y}$ (95% CI: $-0.27$ , 0.05)]. Associations with recent ${\mathrm{NO}}_2$ exposure in women $>80\text{\hspace{0.17em}years of age}$ were stronger and statistically significant when 267 women with incident probable dementia were excluded [e.g., $-0.12/\mathrm{y}$ (95% CI: $-0.22$ , $-0.02$ ) for the cognitively resilient class]. In contrast with changes in CVLT over time, there were no associations between exposures and CVLT scores during follow-up in any subgroup.

Discussion:

In a community-dwelling U.S. population of older women, associations between late-life exposure to ambient air pollution and episodic memory decline varied by age-related cognitive trajectories, exposure time windows, and pollutants. https://doi.org/10.1289/EHP7668