We recently posted an article about the findings of two new studies which suggest a link between the chemicals in air pollution and memory problems, depression and brain shrinkage of the type commonly found in Alzheimer patients*. Now another peer-reviewed scientific study has just been published linking air pollution and Alzheimer’s disease. In this large-scale study, researchers found that among older Americans with cognitive impairment, the greater the air pollution in their neighborhood, the higher the likelihood of amyloid plaques – a hallmark of Alzheimer’s disease.
Study Findings Overview
Researchers examined the PET scans of more than 18,000 seniors with an average age of 75. Participants had dementia or mild cognitive impairment and lived in ZIP codes throughout the nation. The researchers found that those in the most polluted areas had a 10 percent increased probability of a PET scan showing amyloid plaques, compared to those in the least polluted areas.
The primary outcome measure was the association between air pollution and the likelihood of amyloid PET scan positivity, which was measured as odds ratios (ORs) and marginal effects, adjusting for demographic, lifestyle, and socioeconomic factors and medical comorbidities, including respiratory, cardiovascular, cerebrovascular, psychiatric, and neurological conditions.
Dementia Measures: The 18,178 participants had been recruited for the IDEAS study (Imaging Dementia – Evidence for Amyloid Scanning), which had enrolled Medicare beneficiaries whose mild cognitive impairment or dementia** had been diagnosed following comprehensive evaluation.
Air Pollution Measures: Air pollution was estimated at the patient residence using predicted fine particulate matter (PM2.5) and ground-level ozone (O3) concentrations from the Environmental Protection Agency Downscaler model.*** The researchers found that the probability of a positive PET scan rose progressively as concentrations of pollutants increased and predicted a difference of 10 percent probability between the least and most polluted areas.
How Air Pollution Chemicals Could Harm Brain Health
“Exposure in our daily lives to PM2.5, even at levels that would be considered normal, could contribute to induce a chronic inflammatory response. Over time, this could impact brain health in a number of ways, including contributing to an accumulation of amyloid plaques.”
-Leonardo Iaccarino, PhD, researcher, UCSF Memory and Aging Center, Department of Neurology and the UCSF Weill Institute of Neurosciences
A Growing Body of Evidence
This study complements previous large-scale studies suggesting that air pollution is linked to dementia and Parkinson’s disease, and adds additional findings by including a cohort with mild cognitive impairment – a frequent precursor to dementia – and using amyloid plaques as a biomarker of disease.
“This study provides additional evidence to a growing and convergent literature, ranging from animal models to epidemiological studies, that suggests air pollution is a significant risk factor for Alzheimer’s disease and dementia.”
-Gil Rabinovici, MD, researcher, UCSF Memory and Aging Center, Department of Neurology and the UCSF Weill Institute for Neurosciences
This study found that higher PM2.5**** concentrations appeared to be associated with brain Aβ plaques. More specifically, the researchers found that older adults with cognitive impairment who resided in areas with higher concentrations of PM2.5 were more likely to have a positive amyloid PET scan. The associations were statistically significant after adjusting for individualized covariates and showed similar dose-response associations across the whole sample. These findings suggest that brain Aβ accumulation could be one of the biological pathways in the increased incidence of dementia and cognitive decline associated with exposure to air pollution. These findings further suggest the need to consider airborne toxic pollutants associated with Aβ pathology in public health policy decisions and to inform individuals of the lifetime risk of developing Alzheimer’s Disease (AD) and dementia.
*Other studies have linked air pollution to adverse effects on cognitive, behavioral and psychomotor development in children, including a UCSF-University of Washington study that looked at its impact on the IQ of the offspring of pregnant women
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**Not all of the participants were later found to have positive PET scans – 40 percent showed no evidence of plaques on the scan, suggesting non-Alzheimer’s diagnoses like frontotemporal or vascular dementias, which are not associated with the telltale amyloid plaques.
***Air pollution in the neighborhood of each participant was estimated with Environmental Protection Agency data that measured ground-level ozone and PM2.5, atmospheric particulate matter that has a diameter of less than 2.5 micrometers. The researchers also divided locations into quartiles according to the concentration of PM2.5.
****Defined as an inhalable combination of invisible solid and liquid droplets suspended in the air, PM2.5 can be directly emitted (eg, from construction sites or wildfires) and can also result from chemical reactions involving other pollutants. Defined as a colorless harmful gas at ground level, O3 is a component of smog and results from chemical reactions involving emitted molecules, such as volatile organic compounds, with heat and sunlight. Both PM2.5 and O3 have a role in the global burden of disease and mortality and have been associated with an increased risk of cognitive decline, clinically diagnosed Alzheimer’s Disease (AD), and all-cause dementia in epidemiological studies.
Journal Reference: Leonardo Iaccarino, PhD, Renaud La Joie, PhD, Orit H. Lesman-Segev, MD, et al. Association Between Ambient Air Pollution and Amyloid Positron Emission Tomography Positivity in Older Adults With Cognitive Impairment, JAMA Neurology, Published online November 30, 2020. Journal Article/ Press Release/Summary/ doi:10.1001/jamaneurol.2020.3962