Abstract
Observational studies have shown consistently increased likelihood of dementia or mild cognitive impairment diagnoses in people with higher air pollution exposure history, but evidence has been less consistent for associations with cognitive test performance. We estimated the association between baseline neighbourhood-level exposure to airborne pollutants (particulate matter and nitrogen oxides) and (1) cognitive test performance at baseline and (2) cognitive score change between baseline and 2.8-year follow-up, in 86,759 middle- to older-aged adults from the UK Biobank general population cohort. Unadjusted regression analyses indicated small but consistent negative associations between air pollutant exposure and baseline cognitive performance. Following adjustment for a range of key confounders, associations were inconsistent in direction and of very small magnitude. The largest of these indicated that 1 interquartile range higher air pollutant exposure was associated on average with 0.35% slower reaction time (95% CI: 0.13, 0.57), a 2.92% higher error rate on a visuospatial memory test (95% CI: 1.24, 4.62), and numeric memory scores that were 0.58 points lower (95% CI: −0.96, −0.19). Follow-up analyses of cognitive change scores did not show evidence of associations. The findings indicate that in this sample, which is five-fold larger than any previous cross-sectional study, the association between air pollution exposure and cognitive performance was weak. Ongoing follow-up of the UK Biobank cohort will allow investigation of longer-term associations into old age, including longitudinal tracking of cognitive performance and incident dementia outcomes.
Highlights
Outdoor air pollutants such as particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO) and ground-level ozone (O3) are associated with acute and chronic illnesses including cancer, asthma, stroke, heart disease and diabetes[1]
Descriptive information indicated that the sub-group of participants included in the follow-up sample differed in their baseline characteristics from the cross-sectional sample: the follow-up sub-group was somewhat older at baseline, resided in less deprived and less polluted neighbourhoods, scored better on the baseline cognitive tests, and had relatively higher proportions of men, white participants, never-smokers, participants with a degree, and non-urban dwellers
As with the analyses using the centrally-linked pollutant data, all of the false discovery rate (FDR)-adjusted p values were above 0.05, and there were no interactions between the air pollutant measures and time outdoors in any of the models. In this large sample of adults from the UK Biobank general population cohort, cross-sectional associations between air pollutant exposure and cognitive performance attenuated towards the null after adjustment for important confounders
Summary
Outdoor air pollutants such as particulate matter (PM), nitrogen oxides (NOx), carbon monoxide (CO) and ground-level ozone (O3) are associated with acute and chronic illnesses including cancer, asthma, stroke, heart disease and diabetes[1]. There is evidence from animal and human studies that air pollutants are linked to inflammatory processes and morphological changes in the brain, such as upregulation of pro-inflammatory cytokines (including interleukin-1 alpha and beta, interleukin-6 and tumour necrosis factor alpha), activation of microglia and reactive oxygen species, alpha-synuclein deposition, and decreases in dendritic spine density and branching in the hippocampus[7,8,9,10,11] These may result from infiltration of pollutants such as ultrafine particulate matter into brain tissue, via the olfactory nerve or the blood-brain barrier[11,12], with possible contributions through pulmonary inflammation and downstream effects on systemic circulation[13]. A subset of the cohort returned for repeat cognitive assessment between two and seven years post-baseline, permitting both cross-sectional and longitudinal analyses This is the largest study to date of air pollution and cognitive test performance, with standardised measurement of multiple pollutant exposures, cognitive outcomes and potential confounders, in a single general population cohort
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
