Air Pollution and Dementia
| Educator
13th Jan, 2021Quick read

Air Pollution and Dementia

 

Air pollution linked to increased Alzheimer risk in older women

 

Recent evidence suggests a link between fine-particle air pollution and brain shrinkage, a characteristic of Alzheimer’s disease (AD) (1). 

The results of the current prospective cohort study, published in Neurology, found that women living in locations with higher levels of air pollution had a significantly greater risk of brain shrinkage in regions of the brain vulnerable to AD, than women living in areas with lower air pollution levels (1). 

Air pollution is considered a major global health crisis, accounting for an estimated 5 million premature deaths each year (2). Approximately 91% of the world’s population lives in areas where air quality levels exceed the World Health Organisation (WHO) limits (3). Chronic exposure to PM 2.5 air pollution has been linked to increased risk of respiratory, cancer and cardiovascular morbidity and mortality (4,5,6), particularly in the young, elderly and those with pre-existing lung or heart conditions (7). Sources of PM2.5 include mining, coal-fired power generation, diesel vehicles, road and rail transport, solid fuel heaters and prescribed burning.

The current study included 712 women (mean age 77.9±3.7 years) who began the study with no diagnosis of dementia. These women undertook an MRI at baseline, and on average, 4.7 years after the first MRI. The MRI captured high-dimensional grey matter atrophy in regions of the brain vulnerable to AD. AD patterns were assessed using a machine learning tool. 

A spatiotemporal model was created using residential addresses and air monitoring data to estimate the average exposure to air pollution in the three years before the first MRI. Linear models were used to assess the association between PM2.5 and AD patterns after accounting for confounders. 

Each 3 μg/m3 increase in air pollution exposure level was associated with an average increase of 0.03 in brain shrinkage scores over 5 years. These scores were equivalent to a 24% increased risk of AD (1). 

This association remained after adjusting for socioeconomic factors (age, education, employment, income), lifestyle factors, clinical characteristics (diabetes, history of depression, cardiovascular disease, hypertension, hormone therapy) and other factors that can affect brain volume (1). 

Of concern was the observed association between air pollution and brain shrinkage at exposure levels below the current USA EPA  regulatory standard for ambient PM2.5 (1).

Although the mechanisms are unclear, air pollution may contribute to brain aging via direct neurotoxic effects or by increasing cerebrovascular injury (1).

The current study has several limitations: the study population only included older women, exposure in young adulthood and middle age could not be assessed, and only fine particle pollution, not other pollution sources (e.g. traffic emissions or chemicals) were considered. 

Regardless of these limitations, the study’s findings highlight the risk that air pollution poses to human health. These risks include cardiopulmonary disease (8), neuropsychiatric conditions such as schizophrenia (9,10,11), depression and anxiety (12,13,14) and neurological conditions such as Parkinson’s and AD (15).

Air pollution is a modifiable risk factor for many health conditions and the results of the current study can be used with the growing evidence base to inform government strategies for early intervention of AD and other chronic health conditions. 

References
1Younan D, Wang X, Casanova R, Barnard R, Gaussoin SA, Saldana S, Petkus AJ, Beavers DP, Resnick SM, Manson JE, Serre ML. PM2. 5 associated with gray matter atrophy reflecting increased Alzheimers risk in older women. Neurology. 2020 Nov 18.
2BA of Sciences BA, Academy of Science of South Africa. Air Pollution and Health–A Science-Policy Initiative. Annals of Global Health. 2019;85(1).
3World Health Organisation. Air pollution. Retrieved (10 December 2020) https://www.who.int/health-topics/air-pollution#tab=tab_1
4Zhang S, Routledge MN. The contribution of PM 2.5 to cardiovascular disease in China. Environmental Science and Pollution Research. 2020 Jul 20:1-2.
5Pun VC, Kazemiparkouhi F, Manjourides J, Suh HH. Long-term PM2. 5 exposure and respiratory, cancer, and cardiovascular mortality in older US adults. American journal of epidemiology. 2017 Oct 15;186(8):961-9.
6Badyda AJ, Grellier J, Dąbrowiecki P. Ambient PM2. 5 exposure and mortality due to lung cancer and cardiopulmonary diseases in Polish cities. In Respiratory treatment and prevention 2016 (pp. 9-17). Springer, Cham.
7Cheepsattayakorn, A. and Cheepsattayakorn, R. PM2. 5, PM2. 5-related air pollutants, health hazards and impacts on respiratory and cardiovascular disorders and diseases: systematic review and meta-analysis. J Lung Pulm Respir Res, 2019, 6(3), pp.40-48.
8Chi R, Chen C, Li H, Pan L, Zhao B, Deng F, Guo X. Different health effects of indoor‐and outdoor‐originated PM2. 5 on cardiopulmonary function in COPD patients and healthy elderly adults. Indoor air. 2019 Mar;29(2):192-201.
9Worthington MA, Petkova E, Freudenreich O, Cather C, Holt D, Bello I, Diminich E, Tang Y, Ardekani BA, Zeng B, Wu R. Air pollution and hippocampal atrophy in first episode schizophrenia. Schizophrenia Research. 2020 Mar 10.
10Duan J, Cheng Q, Luo X, Bai L, Zhang H, Wang S, Xu Z, Gao J, Zhang Y, Su H. Is the serious ambient air pollution associated with increased admissions for schizophrenia?. Science of the total environment. 2018 Dec 10;644:14-9.
11Gao J, Wei Q, Pan R, Yi W, Xu Z, Duan J, Tang C, He Y, Liu X, Song S, Su H. Elevated environmental PM2. 5 increases risk of schizophrenia relapse: Mediation of inflammatory cytokines. Science of The Total Environment. 2020 Aug 27;753:142008.
12Roberts S, Arseneault L, Barratt B, Beevers S, Danese A, Odgers CL, Moffitt TE, Reuben A, Kelly FJ, Fisher HL. Exploration of NO2 and PM2. 5 air pollution and mental health problems using high-resolution data in London-based children from a UK longitudinal cohort study. Psychiatry research. 2019 Feb 1;272:8-17.
13Pun VC, Manjourides J, Suh H. Association of ambient air pollution with depressive and anxiety symptoms in older adults: results from the NSHAP study. Environmental health perspectives. 2017 Mar;125(3):342-8.
14Shi W, Li T, Zhang Y, Sun Q, Chen C, Wang J, Fang J, Zhao F, Du P, Shi X. Depression and Anxiety Associated with Exposure to Fine Particulate Matter Constituents: A Cross-Sectional Study in North China. Environmental Science & Technology. 2020 Dec 4.
15Shi L, Wu X, Yazdi MD, Braun D, Awad YA, Wei Y, Liu P, Di Q, Wang Y, Schwartz J, Dominici F. Long-term effects of PM2· 5 on neurological disorders in the American Medicare population: a longitudinal cohort study. The Lancet Planetary Health. 2020 Oct 19.