Can air pollution increase risk of Alzheimer’s disease? It may be possible, study of US seniors suggests
People in the most polluted areas had a 10% increased probability of a PET scan showing amyloid plaques, a signature of Alzheimer’s, compared to those in the least polluted areas
Air pollution could be a risk factor for Alzheimer’s disease, the most common cause of dementia globally, according to an analysis led by researchers at the University of California, San Francisco (UCSF). They 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.
The investigators looked at the PET scans of 18,178 seniors in the US whose average age was 75. The participants had dementia or mild cognitive impairment (MCI, which is precursor to dementia) and lived in zip codes across the country. Their analysis reveals that those in the most polluted areas had a 10% increased probability of a PET scan showing amyloid plaques, compared to those in the least polluted areas. When applied to the US population, with an estimated 5.8 million people over 65 with Alzheimer’s, high exposure to microscopic airborne particles may be implicated in tens of thousands of cases, emphasize the authors. The findings have been published in JAMA Neurology.
Scientists believe that a combination of age-related changes in the brain, along with genetic, environmental, and lifestyle factors, likely causes Alzheimer’s. According to the team, their report adds to a body of evidence indicating that pollution from cars, factories, power plants, and forest fires “joins established dementia risk factors like smoking and diabetes.”
“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,” suggests senior author Dr Gil Rabinovici from the UCSF Memory and Aging Center, Department of Neurology and the Weill Institute for Neurosciences.
The plaques and tangles in the brain are considered some of the main features of this irreversible, progressive disorder. In Alzhiermer’s patients, changes in the brain may begin a decade or more before memory and other cognitive problems appear. During this preclinical stage, toxic changes occur in the brain. Abnormal deposits of proteins form amyloid plaques and tau tangles throughout the brain. The once-healthy neurons stop functioning, they lose connections with other neurons, and die. Other complex brain changes are also thought to play a role in Alzheimer’s.
What did the experts find?
The 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 a comprehensive evaluation.
Not all of the participants were later found to have positive PET scans. An estimated 40% showed no evidence of plaques on the scan, suggesting non-Alzheimer’s diagnoses like “frontotemporal or vascular dementias,” which are not associated with amyloid plaques, says the team. It also inlcudes experts from Brown University School of Public Health, Virginia Commonwealth University, Washington University School of Medicine, Kaiser Permanente, and the Alzheimer’s Association.
Air pollution in the neighborhood of each participant was estimated with the Environmental Protection Agency (EPA) data that measured ground-level ozone, and PM2.5 or atmospheric particulate matter that has a diameter of fewer than 2.5 micrometers. The researchers also divided locations into quartiles according to the concentration of PM2.5. They found that the probability of a positive PET scan rose progressively as concentrations of pollutants increased.
“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,” writes first author Dr Leonardo Iaccarino. He is also from the UCSF Memory and Aging Center, Department of Neurology, and the Weill Institute of Neurosciences.
According to the investigators, the findings suggest the need to consider “airborne toxic pollutants associated with Aβ (Amyloid beta) pathology” in public health policy decisions and to inform individual lifetime risk of developing Alzheimer’s and dementia.