Air Pollution Linked to Brain Amyloid Pathology

December 02, 2020

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.

Dr Leonardo Iaccarino

"Many studies have now found a link between air pollution and clinical outcomes of dementia or cognitive decline," lead author Leonardo Iaccarino, PhD, Weill Institute for Neurosciences, University of California, San Francisco, told Medscape Medical News. "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," 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."

The study was published online in JAMA Neurology on November 30.

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 US participants with cognitive impairment who received an amyloid positron-emission tomography (PET) 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 US Environmental Protection Agency were used to estimate air quality in individual ZIP-code areas during two periods ― 2002 to 2003 (approximately 14 years before the amyloid PET scan) and 2015 to 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," 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," Iaccarino said.

Exposure to higher ozone concentrations was not associated with amyloid positivity on PET scans in both time windows.

"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 state.

"Adverse effects of airborne toxic pollutants associated with amyloid-beta pathology should be considered in public health policy decisions and should inform individual lifetime risk of developing Alzheimer's disease and dementia," they conclude.

Iaccarino noted that although governments need to take primary action in reducing air pollution, individuals can make some changes to reduce their exposure to poor-quality air.

"Such changes could include not going out or using masks when pollution levels are very high (as happened recently in California with the wild fires) and avoiding areas where the air quality is known to be bad. In addition, there are activities which increase indoor air pollution which can be changed, such as certain types of cooking, cigarette smoking, use of coal fires," he commented.

"Based on our findings, it would be reasonable to take action on these things, especially for individuals at higher risk of cardiovascular and respiratory disease or Alzheimer's," he added.

On a more optimistic note, Iaccarino pointed out that air quality in the United States has improved significantly in recent years. Meaningful improvements were found between the two periods in this analysis study (2002–2016), "so we are going in the right direction."

The IDEAS Study was funded by the Alzheimer's Association, the American College of Radiology, Avid Radiopharmaceuticals Inc, GE Healthcare, and Life Molecular Imaging. Iaccarino has disclosed no relevant financial relationships.

JAMA Neurol. Published online November 30, 2020. Abstract

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