Air pollution linked to depressive symptoms, episodic memory decline among older women

Late-life air pollution exposure among women aged 80 years or older appeared associated with increased risk for depressive episodes and episodic memory declines, according to study results published in Journal of the American Geriatrics Society.

“A U-shaped curve of depressive symptoms exists across older adulthood, with late-life [depressive symptoms] decreasing during the early period of older adulthood with an uptick in the oldest-old,” Andrew J. Petkus, PhD, of the department of neurology at USC, and colleagues wrote. “Declines in episodic memory become more pronounced after age 80 and typically co-occur with [depressive symptoms]. There is considerable environmental influence on the etiology of both [depressive symptoms] and [episodic memory].”

The researchers noted that the effect of physical environments on individuals aged 80 years or older has been understudied. To address this research gap, they analyzed data of 1,583 dementia-free women in this age group who were included in the Women’s Health Initiative Memory Study-Epidemiology of Cognitive Health Outcomes, a geographically diverse community-dwelling population. Participants completed up to six annual memory assessments via the latent composite of East Boston Memory Test and Telephone Interview for Cognitive Status, as well as the 15-item Geriatric Depression Scale (GDS-15). Petkus and colleagues used regionalized national universal kriging to estimate 3-year average exposures to regional particulate matter with aerodynamic diameter below 2.5 m (PM_2.5) and gaseous nitrogen dioxide at baseline and during a remote period 10 years earlier.

The researchers used latent change structural equation models to assess whether living in areas with higher pollutant levels was linked to annual changes in standardized episodic memory and depressive symptoms while adjusting for potential confounders. Results showed a significant link between remote NO₂ and PM_2.5 exposure and larger increases in standardized depressive symptoms; however, the magnitude of the difference, which was less than one point on the GDS-15, was of questionable clinical significance, the researchers noted. Further, higher depressive symptoms were linked to accelerated declines in episode memory, with a significant indirect effect of remote NO₂ and PM_2.5 exposure on declines in episodic memory mediated by depressive symptoms. Petkus and colleagues observed no other significant indirect exposure effects.

“Our study provides epidemiological evidence that living in areas with higher levels of PM_2.5 and NO₂ in late life may contribute directly to increased [depressive symptoms], of small magnitude, and indirectly to declines in [episodic memory] of the oldest-old women,” the researchers wrote. “These findings highlight that the adverse effect of air pollution on the interplay between [depressive symptoms] and [episodic memory] is heterogeneous, likely varying by pollutants and age.”