Cognitive Performance and Long-term Exposure to Outdoor Air Pollution: Findings from the Harmonised Cognitive Assessment Protocol Sub-Study of the English Longitudinal Study of Ageing (ELSA-HCAP)

Background Although air pollution is associated with worse cognitive performance, whether these relationships differ by cognitive domain and which sources of air pollution are particularly detrimental to cognition remains understudied. This study examined associations between cognitive scores across three domains in older adults and 8-10 years of exposure to air pollutants (NO2, total PM2.5, and PM2.5 from different emission sources). Methods We used data from the 2018 Harmonized Cognitive Assessment Protocol sub-study of the English Longitudinal Study of Ageing (N=1,127). Outdoor concentrations of each pollutant were estimated for 2008/10-2017 and summarised using means and group-based trajectories. Linear regression models were used to assess long-term air pollution exposure relationships with memory, executive function, language, and global cognitive function after adjustment for key individual and neighbourhood-level confounders. Results Associations between air pollution trajectories and cognition are mostly inverted j-shaped, with respondents exposed to the highest residential levels of NO2 and total PM2.5 having worse performance for global cognition [β=-0.241; 95%CI=(-0.46,-0.02) and β=-0.334; 95%CI=(-0.55,-0.12) respectively] than those exposed to average levels of pollution. Similar associations were also found for executive function and memory (PM2.5 only), whereas more compelling dose-response evidence was found for language. Higher emissions from industry and residential combustion, as well as biofuel, coal, oil and natural gas combustion, were associated with worse language scores. Conclusions Air pollution and its sources have domain-specific associations with cognitive performance, with most consistent evidence observed for language. Continued efforts to reduce air pollution, particularly where levels are the highest, might benefit cognitive performance.