Air Pollution is Associated with Increased Amyloid-β Plaques in Older Individuals with Cognitive Impairment
Post by Amanda McFarlan
What's the science?
Alzheimer’s disease is a neurodegenerative disease associated with the accumulation of amyloid-β plaques and neurofibrillary tangles. It has been suggested that environmental factors like air pollution may contribute to the development of Alzheimer’s disease. Indeed, human and animal studies have provided evidence that exposure to air pollution may lead to increased production and deposition of amyloid-β in the brain. This week in JAMA Neurology, Iaccarino and colleagues investigated whether increased levels of air pollution are associated with the accumulation of amyloid plaques in the brains of older individuals with cognitive impairment.
How did they do it?
The authors obtained data from the Imaging Dementia—Evidence for Amyloid Scanning (IDEAS) study which assessed amyloid-β accumulation in over 18 000 participants with cognitive impairment using positron emission tomography (PET). They also obtained demographic information as well as residential zip code data for all participants in the study. Then, they used the Downscaler model provided by the United States Environmental Protection Agency to gather data on the air quality, as measured by fine particulate matter (particles with a diameter less than 2.5 μm) and ground-level ozone, from 2002-2003 (~14 years prior to the PET scan) and from 2015-2016 (~1 year prior to the PET scan). Using this data, the authors performed statistical analyses to determine whether participants living in areas with higher levels of fine particulate matter and ground-level ozone were more likely to be positive at the amyloid-PET scan, indicating brain amyloid-β accumulation.
What did they find?
The authors found that the probability of detecting amyloid-β in the participants’ PET scans was significantly increased in areas with higher concentrations of fine particulate matter. They used marginal effects analyses to show that for every 1 μg/m3 increase in fine particulate matter, the probability of having a positive amyloid PET scan was +0.5% in 2002-2003 and +0.8% in 2015-2016. The association between positive amyloid PET scans and fine particulate matter remained statistically significant after adjusting for covariates including sex and US Census tract (distinct geographic regions that are used for the exchange of geographic and statistical data) random effects. Higher concentrations of ground-level ozone, on the other hand, were not associated with positive amyloid PET scans.
What’s the impact?
This study shows that the regional concentration of fine particulate matter in the air is associated with increased accumulation of amyloid-β plaques in the brains of older individuals with cognitive impairment. These findings suggest that airborne pollutants may be associated with Alzheimer’s disease pathology. These findings can inform public health policy decisions, as pollution levels may contribute to an individual’s risk of developing Alzheimer’s and dementia.
Iaccarino et al. Association Between Ambient Air Pollution and Amyloid Positron Emission Tomography Positivity in Older Adults With Cognitive Impairment. JAMA Neurology (2020). Access the original scientific publication here.