Alzheimer's and Air Quality

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Alzheimer's and Air Quality

RESEARCH STUDIES

1. Air Pollution and Dementia: A Systematic Review.

  • This article, published in 2019, was written by researchers R. Peters, N. Ee, J. Peters, A. Booth, I. Mudway, and KJ Anstey and published in the Journal of Alzheimer's Disease.
  • The article compiles a systemic review of various research studies, including ones from Medline, Embase, and PsychINFO, dating back to September of 2018, and looked both at general air pollution as well as at smoke-related air pollution.
  • In total, they reviewed 13 separate studies and papers on the subject matter, with follow-up periods ranging from one year to 15.
  • Researchers ultimately concluded that "evidence is emerging that greater exposure to airborne pollutants is associated with increased risk of dementia".

2. Traffic-Related Air Pollution and Dementia Incidence in Northern Sweden: A Longitudinal Study

  • This study was published in March of 2016 by Environmental Health Perspectives, and was written by Anna Oudin, Bertil Forsberg, Annelie Nordin Adolfsson, Nina Lind, Lars Modig, Maria Nordin, Steven Nordin, Rolf Adolfsson, and Lars-Göran Nilsson.
  • The researchers entered the study with the goal of "[assessing] the association between long-term exposure to traffic-related air pollution and dementia incidence in a major city in northern Sweden".
  • Ultimately, the study found that "participants in the group with the highest exposure were more likely than those in the group with the lowest exposure to be diagnosed with dementia (Alzheimer’s disease or vascular dementia)". More specifically, the incidence rate of vascular dementia was slightly higher, but by less than a single percentage point.
  • In their conclusion, the researchers wrote that "if the associations we observed are causal, then air pollution from traffic might be an important risk factor for vascular dementia and Alzheimer’s disease".

3. Exposure to ambient air pollution and the incidence of dementia: A population-based cohort study

  • This article was published by Environmental International in November of 2017, by authors Hong Chen, Jeffrey C. Kwong, Ray Copes, Perry Hystad, Aaronvan Donkelaar, Karen Tu, Jeffrey R. Brook, Mark S. Goldberg, Randall V. Martin, Brian J. Murray, Andrew S. Wilton, Alexander Kopp, and Richard T. Burnett.
  • The study was based in Canada, and focused specifically on Ontario. More specifically, the "study population comprised all Ontario residents who, on 1 April 2001, were 55–85 years old, Canadian-born, and free of physician-diagnosed dementia".
  • In total, researchers followed the roughly 2.1 million participants for 12 years, from 2001 to 2013.
  • At the end of the study, which looked both at dementia incidence rates and at Ontario's air quality throughout those years, the researchers concluded that "exposure to air pollution, even at the relative low levels, was associated with higher dementia incidence".

4. Exposure to air pollution as a potential contributor to cognitive function, cognitive decline, brain imaging, and dementia: A systematic review of epidemiological research

  • This article was written by researchers Melinda C. Power, Sara D. Adar, Jeff D. Yanosky, and Jennifer Weuve. It was published in September of 2016 in Volume 56 of NeuroToxicology.
  • The report was a systemic review of existing research and epidemiology on the subject of air quality and cognitive function and decline. In the summary of their methods, the researchers wrote that "we undertook a systematic review, including quality assessment, to interpret the collective findings and describe methodological challenges that may limit study validity. Articles, which were identified according to a registered protocol, had to quantify the association of an air pollution exposure with cognitive function, cognitive decline, a dementia-related neuroimaging feature, or dementia".
  • In total, they reviewed 18 relevant studies and articles and found that, while they all "reported an adverse association between at least one pollutant and one dementia-related outcome", very few of them could definitively identify a clear link or causal relationship between air quality and dementia or Alzheimer's.

5. Ambient air pollution and neurotoxicity on brain structure: Evidence from women's health initiative memory study

  • Found in the Anals of Neurology, this article was published by Jiu‐Chiuan Chen, Xinhui Wang, Gregory A. Wellenius, Marc L. Serre, Ira Driscoll, Ramon Casanova, John J. McArdle, JoAnn E. Manson, Helena C. Chui, and Mark A. Espeland in June of 2015.
  • The authors wrote that "the aim of this study was to examine the putative adverse effects of ambient fine particulate matter...on brain volumes in older women". As such, researchers looked at 1,403 community‐dwelling older women without dementia enrolled in the Women's Health Initiative Memory Study between 1996 and 1998. Brain scans were performed seven to eight years later, from 2005-2006, when the participants were between the ages of 71 and 89.
  • "Given residential histories and air monitoring data, we used a spatiotemporal model to estimate cumulative PM2.5 exposure in 1999–2006. Multiple linear regression was employed to evaluate the associations between PM2.5 and brain volumes, adjusting for intracranial volumes and potential confounders."
  • Ultimately, they concluded that further research would be necessary, but that exposure to poor air quality and air pollution could contribute to loss of white matter in older women, thereby contributing to neurological decline.

6. Hazed and Confused: The Effect of Air Pollution on Dementia

  • This study was published in August of 2018 and revised in August of 2019, by the National Bureau of Economic Research. Researchers on the study included Kelly C. Bishop, Jonathan D. Ketcham, and Nicolai V. Kuminoff.
  • The study looked specifically at older Americans, with a focus on Medicare recipients and their "cumulative residential exposures to PM2.5 and their health from 2004 through 2013, leveraging within- and between-county quasi-random variation in PM2.5 resulting from the expansion of Clean Air Act regulations".
  • Ultimately, their research found "that long-term exposure to fine-particulate air pollution (PM2.5) degrades health and human capital among older adults by increasing their risk of developing Alzheimer’s disease and related dementias". More specifically, the paper's abstract indicates that "a 1 ìg/m3 increase in decadal PM2.5 increases the probability of a dementia diagnosis by 1.68 percentage points. The effects are as large or larger when we adjust for mortality-based sample selection and additional Tiebout-sorting dynamics".

7. Prefrontal white matter pathology in air pollution exposed Mexico City young urbanites and their potential impact on neurovascular unit dysfunction and the development of Alzheimer's disease

  • This study was published by Lilian Calderón-Garcidueñas, Rafael Reynoso-Robles, Javier Vargas- Martínez, Aline Gómez-Maqueo-Chew, Beatriz Pérez-Guillé, Partha S. Mukherjee, Ricardo Torres Jardón, George Perry, and Angélica Gónzalez-Maciel in April of 2016.
  • It is available to read in Volume 146 of Environmental Research.
  • The report's abstract notes that "millions of urban children are chronically exposed to high concentrations of air pollutants, i.e., fine particulate matter (PM2.5) and ozone, associated with increased risk for Alzheimer's disease", and focused specifically on Mexico City.
  • More specifically, the researchers found that children in Mexico City - being exposed to more significant levels of air pollution than other children - "exhibit systemic, brain and intrathecal inflammation, low CSF Aβ42, breakdown of the BBB, attention and short-term memory deficits, prefrontal white matter hyperintensities, damage to epithelial and endothelial barriers, tight junction and neural autoantibodies, and Alzheimer and Parkinson's hallmarks".

NEWS ARTICLES AND REPORTS

1. Air Pollution May Damage the Brain

  • Published by the New York Times, this article was written by Nicholas Bakalar on November 25, 2019.
  • The article, which looks at the topic of air pollution and brain health, examines a study published that month in Brain.
  • In his article, Bakalar summarizes the study, writing that "long-term exposure to air pollution is associated with lower scores on tests of mental acuity, researchers have found. And one reason may be that air pollution causes changes in brain structure that resemble those of Alzheimer’s disease".

2. The Evidence Is Strong: Air Pollution Seems to Cause Dementia

  • Written by Aaron Reuben, this article was published in Wired on May 9, 2019.
  • The author writes that, while the connection between air quality and dementia has been known for years, more recent research is strengthening the connection while also pointing out the decreased air quality throughout the world. In fact, he writes that many researchers believe that studies on the subject are "conclusive", drawing a clear and definite connection between air pollution and dementia.
  • The article references and summarizes the findings of various studies and researchers, noting that the causal effect between poor air quality and decreased brain function has been well-studied.

3. Alzheimer's: Poor air quality may contribute to cognitive decline

  • This article was published in Medical News Today on November 22, 2019, by author Maria Cohut.
  • The article focuses primarily on a research study published by Brain, but references other data, findings, and resources as well.
  • In the article, Cohut notes that "more evidence points to the idea that air pollution may increase the risk of Alzheimer's disease. A new study suggests that tiny polluting particles carried by dirty air can enter the brain, possibly contributing to cognitive decline".

4. Air pollution linked to much greater risk of dementia

  • This article was published in The Atlantic on September 18, 2018, and was written by Fiona Harvey.
  • While the article notes that people of all ages are at greater risk of developing dementia due to air pollution, it indicates that people over 50 are at the greatest risk.
  • "People over 50 in areas with the highest levels of nitrogen oxide in the air showed a 40% greater risk of developing dementia than those with the least NOx pollution, according to the research, based on data from London."
  • Primarily, Harvey summarizes the results of a study on the subject. However, the article also references existing research on the topic, noting that this latest study contributes to a growing body of research which draws a clear connection between air pollution and dementia.

5. USC study connects air pollution, memory problems and Alzheimer’s-like brain changes

  • Written by Leigh Hopper, this article was published by USCNews on November 20, 2019.
  • Hopper opens the piece by writing that "women in their 70s and 80s who were exposed to higher levels of air pollution experienced greater declines in memory and more Alzheimer’s-like brain atrophy than their counterparts who breathed cleaner air, according to USC researchers".
  • Primarily, the article summarizes the study referenced in that first paragraph, which was published in Brain last year, noting what the particulars and focus of the study were and that it "is the first study to really show, in a statistical model, that air pollution was associated with changes in people’s brains and that those changes were then connected with declines in memory performance".

6. Is air pollution tied to higher dementia risk?

  • In an article published by CNN on September 18, 2018, author Jacqueline Howard writes that "scientists have long known that breathing dirty air can be bad for your health, including your brain health".
  • Howard goes on to summarize a study published in 2018 which, she writes, shows "just how much exposure to high amounts of air and noise pollution could be linked with an increased risk of dementia".
  • "Specifically, those in the top fifth areas of exposure "were 40% more likely to be diagnosed with dementia in the study" than those in the bottom fifth, even after adjusting for other risk factors like smoking or socioeconomic status, said Iain Carey, a senior lecturer of epidemiology in the Population Health Research Institute at St. George's University of London, who was lead author of the paper."

7. A New Study Links Air Pollution With Alzheimer’s

  • This article was published in Slate on September 4, 2018, and was written by Henry Grabar.
  • In the article, Grabar summarizes and discusses the research article Hazed and Confused (linked and summarized above).
  • He goes further though, to note the study's timeliness in connection with EPA plans to loosen sanctions which ensure cleaner air regulations.
  • "It’s the second recent study to make the connection between cognition and pollution. In August, a study published in the Proceedings of the National Academy of Sciences determined that in Chinese cities, where smog can hide the sun for weeks at a time, long-term exposure to pollution was linked to declining test scores—especially in older men."

AIR QUALITY AND BRAIN HEALTH

Air Quality and White Matter

  • A number of recent studies on the subject of poor air quality and dementia have found that "prefrontal white matter is a target of air pollution", potentially explaining how air pollution is contributing to dementia, Alzheimer's, and other neurological deficits.
  • More specifically, white matter hyperintensities - which are typically seen in the brain scans of older patients - "are associated with increased likelihood of cognitive impairment and dementia".
  • While this condition is typically observed in older patients - those most likely to experience memory and other cognitive impairments - the connection between white matter loss and poor air quality suggests that this target is why air pollution has been linked to increased incidences of dementia.

Traffic-Related Air Pollution

  • Though there are a number of studies on the connection between poor air quality and dementia, several exist which look specifically at the impact of traffic-related air pollution.
  • For example, a 2016 study in Sweden noted that "air pollution from traffic might be an important risk factor for vascular dementia and Alzheimer's disease". The study looked at residents living in areas of high traffic and who did not previously have a diagnosis of or relating to dementia or Alzheimer's disease.
  • Similarly, a study which took place in Ontario over the course of 10 years "found that those who lived closer to major high-traffic roads were significantly more likely to develop Alzheimer’s disease across the study period, regardless of their health at baseline or socioeconomic status".
  • Another study looked at mice and dogs which were exposed to traffic pollution and noted "symptoms such as poorer learning ability, memory and motor skills" in the test subjects.

Smoking and Dementia

  • The World Health Organization has identified smoking as an official risk factor for dementia and Alzheimer's, noting that patients who smoke are at greater risk of developing the condition.
  • More specifically, smoking and smoke inhalation - such as via second-hand smoke and poor air quality - can "increase oxidative stress and inflammation, which have both been linked to developing of Alzheimer's disease".
  • "There is strong evidence that smoking can increase your risk of dementia. Not everyone who smokes will get dementia, but stopping smoking is thought to reduce your risk down to the level of non-smokers."
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