A critical review of the epidemiological evidence of effects of air pollution on dementia, cognitive function and cognitive decline in adult population

Juana Maria Delgado-Saborit*, Valentina Guercio, Alison M. Gowers, Gavin Shaddick, Nick C. Fox, Seth Love

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

4 Citations (Scopus)

Abstract

Dementia is arguably the most pressing public health challenge of our age. Since dementia does not have a cure, identifying risk factors that can be controlled has become paramount to reduce the personal, societal and economic burden of dementia. The relationship between exposure to air pollution and effects on cognitive function, cognitive decline and dementia has stimulated increasing scientific interest in the past few years. This review of the literature critically examines the available epidemiological evidence of associations between exposure to ambient air pollutants, cognitive performance, acceleration of cognitive decline, risk of developing dementia, neuroimaging and neurological biomarker studies, following Bradford Hill guidelines for causality. The evidence reviewed has been consistent in reporting associations between chronic exposure to air pollution and reduced global cognition, as well as impairment in specific cognitive domains including visuo-spatial abilities. Cognitive decline and dementia incidence have also been consistently associated with exposure to air pollution. The neuro-imaging studies reviewed report associations between exposure to air pollution and white matter volume reduction. Other reported effects include reduction in gray matter, larger ventricular volume, and smaller corpus callosum. Findings relating to ischemic (white matter hyperintensities/silent cerebral infarcts) and hemorrhagic (cerebral microbleeds) markers of cerebral small vessel disease have been heterogeneous, as have observations on hippocampal volume and air pollution. The few studies available on neuro-inflammation tend to report associations with exposure to air pollution. Several effect modifiers have been suggested in the literature, but more replication studies are required. Traditional confounding factors have been controlled or adjusted for in most of the reviewed studies. Additional confounding factors have also been considered, but the inclusion of these has varied among the different studies. Despite all the efforts to adjust for confounding factors, residual confounding cannot be completely ruled out, especially since the factors affecting cognition and dementia are not yet fully understood. The available evidence meets many of the Bradford Hill guidelines for causality. The reported associations between a range of air pollutants and effects on cognitive function in older people, including the acceleration of cognitive decline and the induction of dementia, are likely to be causal in nature. However, the diversity of study designs, air pollutants and endpoints examined precludes the attribution of these adverse effects to a single class of pollutant and makes meta-analysis inappropriate.

Original languageEnglish
Article number143734
Number of pages27
JournalScience of the Total Environment, The
Volume757
DOIs
Publication statusPublished - 25 Feb 2021

Bibliographical note

Funding Information:
This work has been conducted as a part of a wider report for the UK's Committee on the Medical Effects of Air Pollutants (COMEAP) on cognitive decline, dementia and air pollution. We would like to express our sincere gratitude to Robert L Maynard, chair of the COMEAP Sub-group on the Effects of Exposure to Air Pollutants on Cognitive Decline and Dementia, for his useful discussions and comments to earlier versions of this manuscript. We thank Ian Mudway, Roxana Carare and Jonathan Grigg for their ideas and comments during early COMEAP Sub-group taskforce meetings. We wish to acknowledge the members of COMEAP for their ideas and comments on an earlier, more limited review of the available literature, with special thanks to Deborah Jarvis for her constructive comments. Juana Maria Delgado-Saborit is a recipient of funds from the European Union's Horizon 2020 – Research and Innovation Framework Programme under the Marie Skłodowska-Curie grant agreement no 750531 . Juana Maria Delgado-Saborit acknowledges the support by the Generalitat Valenciana through the “Plan GenT” program ( CIDEGENT/2019/064 grant).

Funding Information:
This work has been conducted as a part of a wider report for the UK's Committee on the Medical Effects of Air Pollutants (COMEAP) on cognitive decline, dementia and air pollution. We would like to express our sincere gratitude to Robert L Maynard, chair of the COMEAP Sub-group on the Effects of Exposure to Air Pollutants on Cognitive Decline and Dementia, for his useful discussions and comments to earlier versions of this manuscript. We thank Ian Mudway, Roxana Carare and Jonathan Grigg for their ideas and comments during early COMEAP Sub-group taskforce meetings. We wish to acknowledge the members of COMEAP for their ideas and comments on an earlier, more limited review of the available literature, with special thanks to Deborah Jarvis for her constructive comments. Juana Maria Delgado-Saborit is a recipient of funds from the European Union's Horizon 2020 ? Research and Innovation Framework Programme under the Marie Sk?odowska-Curie grant agreement no 750531. Juana Maria Delgado-Saborit acknowledges the support by the Generalitat Valenciana through the ?Plan GenT? program (CIDEGENT/2019/064 grant).

Publisher Copyright:
© 2020 The Authors

Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.

Keywords

  • Air pollution
  • Cognitive function
  • Dementia
  • NO
  • O
  • PM
  • ROAD TRAFFIC NOISE
  • HOSPITAL ADMISSIONS
  • ALZHEIMERS-DISEASE
  • LONG-TERM EXPOSURE
  • NEUROLOGICAL DISORDERS
  • ENVIRONMENTAL-FACTORS
  • NO2
  • RESIDENTIAL PROXIMITY
  • O-3
  • BODY-MASS INDEX
  • MAJOR ROADS
  • FINE PARTICULATE MATTER

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