Association of Air Pollution with Memory Decline Later in Life in the United States

Abstract Background Emerging evidence suggests that air pollution exposure might diminish the cognitive health of older adults. Although many studies have reported that air pollution is associated with increased dementia risk, associations with the process of cognitive decline have been more heterogeneous. Method We used biennial data between 2000 to 2016 from respondents>65 years in the Health and Retirement Study (HRS), a national, population‐based cohort in the United States, to study associations of air pollution with cognitive decline. We assessed episodic memory as a composite score of performance on immediate and delayed recall tests combined with proxy‐reported memory function. We standardized the memory score at baseline and during follow‐up based on its baseline mean (0.66) and standard deviation (0.69). We used spatiotemporal models to predict 10‐year average particulate matter (PM 2.5 , PM 10‐2.5 ), nitrogen dioxide (NO 2 ) and ozone (O 3 ) at participant residences before each interview. Associations with rates of memory decline were estimated by generalized estimating equation regression, adjusting for individual demographics, area‐level characteristics, time, and spatial trends. Result Among the 19,063 participants during an average of 7.4±5.3 years of follow‐up time, the mean age at baseline was 71.0±7.3 years. The mean (interquartile range, IQR) PM 2.5, PM 10‐2.5 , NO 2 and O 3 concentrations were 12.2 (3.6) µg/m 3 , 9.4 (4.6) µg/m 3 , 11.2 (7.8) ppb and 26.6 (3.7) ppb respectively. In single‐pollution models, we observed consistently steeper decline in episodic memory scores with higher PM 2.5 , PM 10‐2.5 and NO 2 long‐term concentrations (all approximately ‐0.003 standard units/year per IQR, 95%CI: ‐0.006, ‐0.0004), whereas the reverse was observed with higher exposures to O 3 (0.003 standard units/year per IQR, 95%CI: 0.001, 0.005) . Associations were changed to null for PM 2.5 and NO 2 , and slightly attenuated for O 3 after adjustment for other pollutants in the multi‐pollutant model. Conclusion This study suggests that long‐term exposure to air pollution might be associated with cognitive decline among older adults though the results differed by pollutant.