Higher levels of air pollution were associated with an increased risk for amyloid-beta pathology in a new study of older adults with cognitive impairment. “Many studies have now found a link between air pollution and clinical outcomes of dementia or cognitive decline,” said lead author Leonardo Iaccarino, PhD, Weill Institute for Neurosciences, University of California, San Francisco. “But this study is now showing a clear link between air pollution and a biomarker of Alzheimer’s disease: It shows a relationship between bad air quality and pathology in the brain.
“We believe that exposure to air pollution should be considered as one factor in the lifetime risk of developing Alzheimer’s disease,” he added. “We believe it is a significant determinant. Our results suggest that, if we can reduce occupational and residential exposure to air pollution, then this could help reduce the risk of Alzheimer’s disease.”
The study was published online Nov. 30 in JAMA Neurology.
A modifiable risk factor
Dr. Iaccarino explained that it is well known that air pollution is linked to poor health outcomes. “As well as cardiovascular and respiratory disease, there is also growing interest in the relationship between air pollution and brain health,” he said. “The link is becoming more and more convincing, with evidence from laboratory, animal, and human studies suggesting that individuals exposed to poor air quality have an increased risk of cognitive decline and dementia.”
In addition, this year, the Lancet Commission included air pollution in its updated list of modifiable risk factors for dementia.
For the current study, the researchers analyzed data from the Imaging Dementia–Evidence for Amyloid Scanning (IDEAS) Study, which included more than 18,000 U.S. participants with cognitive impairment who received an amyloid positron-emission tomography scan between 2016 and 2018.
The investigators used data from the IDEAS study to assess the relationship between the air quality at the place of residence of each patient and the likelihood of a positive amyloid PET result. Public records from the U.S. Environmental Protection Agency were used to estimate air quality in individual ZIP-code areas during two periods – 2002-2003 (approximately 14 years before the amyloid PET scan) and 2015-2016 (approximately 1 year before the amyloid PET scan).
Results showed that those living in an area with increased air pollution, as determined using concentrations of predicted fine particulate matter (PM2.5), had a higher probability of a positive amyloid PET scan. This association was dose dependent and statistically significant after adjusting for demographic, lifestyle, and socioeconomic factors as well as medical comorbidities. The association was seen in both periods; the adjusted odds ratio was 1.10 in 2002-2003 and 1.15 in 2015-2016.
“This shows about a 10% increased probability of a positive amyloid test for individuals living in the worst polluted areas, compared with those in the least polluted areas,” Dr. Iaccarino explained.
Every unit increase in PM2.5 in 2002-2003 was associated with an increased probability of positive amyloid findings on PET of 0.5%. Every unit increase in PM2.5 in for the 2015-2016 period was associated with an increased probability of positive amyloid findings on PET of 0.8%.
“This was a very large cohort study, and we adjusted for multiple other factors, so these are pretty robust findings,” Dr. Iaccarino said.
Exposure to higher ozone concentrations was not associated with amyloid positivity on PET scans in either time window.
“These findings suggest that brain amyloid-beta accumulation could be one of the biological pathways in the increased incidence of dementia and cognitive decline associated with exposure to air pollution,” the researchers stated.