The English Longitudinal Study of Ageing followed 12,235 adults aged 50 and over across ten waves from 2002-03 to 2021-23. Each person's number of days above the WHO daily guideline for NO2, PM2.5 and PM10 was derived from residence-linked estimates for the preceding calendar year. Comparing someone at the 75th percentile of such days with someone at the median, estimated 14-year decline in episodic memory was 0.09 SD greater. Days above the PM2.5 and PM10 guidelines were not associated with decline, and no pollutant was associated with performance at baseline. Exposure was counted for a single year before baseline and at the home address rather than where people spent their days.
Why it is interesting: For NO2, the count of days above the daily guideline carried a signal that the annual mean did not. It bears on how air quality is measured against guidelines and on work on dementia risk factors.
Abstract — the authors' own words, CC BY
Importance
Long-term exposure to higher average air pollutant concentrations is associated with poorer cognitive health, but annual averages can obscure substantial differences in day-to-day exposure. Whether recurrent high pollution days are associated with long-term cognitive aging trajectories among people with similar overall air pollution exposure is unclear. Objective
To determine whether the annual number of days exceeding World Health Organization daily guideline values for nitrogen dioxide (NO 2 ) and particulate matter (PM 2.5 and PM 10 ) is associated with subsequent cognitive decline after accounting for annual mean air pollutant exposure. Design
Prospective cohort study using data from waves 1-10 (2002-03 to 2021-23) of the English Longitudinal Study of Ageing. Setting
Population-based cohort of community-dwelling adults in England. Participants
12,235 adults aged 50+ years at analytic baseline. Exposures
Number of days exceeding World Health Organization daily guideline values (‘exceedance days’) for NO 2 , PM 2.5 , and PM 10 , derived from residence-linked environmental estimates during the calendar year preceding the analytic baseline. Main Outcomes and Measures
Baseline cognitive performance and model-estimated 14- year cognitive decline (corresponding to the 75th percentile of follow-up duration) in episodic memory and verbal fluency. Results
Exceedance days were not associated with baseline memory or verbal fluency after adjustment for annual mean air pollutant exposure. More NO 2 exceedance days were associated with faster cognitive decline: comparing the 75th percentile with the median of NO 2 exceedance days, the difference in 14-year decline was -0.09 SD (95% CI, -0.17 to -0.01; p = 0.02) for memory and -0.10 SD (95% CI, -0.19 to 0.00; p = 0.04) for fluency. PM 2.5 and PM 10 exceedance days were not associated with cognitive decline. Conclusions and Relevance
In this cohort study of older adults, a higher number of NO 2 exceedance days was associated with faster subsequent cognitive decline after adjustment for annual mean air pollutant exposure. This suggests that daily exposure to high NO 2 concentrations may be related to accelerated cognitive aging even when offset by lower exposure on other days, potentially providing a new rationale for identifying and prioritizing areas with recurrent high NO 2 exposure and the local emission sources contributing to it. Key points
Question
Among individuals with similar average air pollution exposure but different day-to-day exposure patterns, are more high pollution days associated with faster cognitive decline? Findings
In this UK-based cohort of 12,235 adults aged 50+, individuals exposed to more days on which nitrogen dioxide (NO 2 ) concentrations exceeded World Health Organization guideline values subsequently had significantly faster cognitive decline over up to 18 years, after adjustment for annual mean air pollutant exposure. No associations were observed for particulate matter. Meaning
Daily exposure to high NO 2 concentrations is associated with faster cognitive decline even when offset by lower concentrations on other days.
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