Clinical Relevance: Consider air pollution as a potential factor influencing cognitive health
- A new study adds to a body of evidence connecting air pollution to an elevated risk of dementia.
- The detailed analysis found that dementia risk is notably connected to exposure to PM2.5 from wildfire smoke and agricultural activities.
- There is an essential role for comprehensive policy measures to address the threat posed by bad air to brain health.
A new nationwide study adds to the growing evidence that long-term exposure to air pollution is associated with an increased risk of developing dementia. The research, published in JAMA Internal Medicine, found that American seniors living in regions with higher levels of fine particulate matter (PM2.5) pollution had an eight percent greater risk of developing dementia over a 10-year period.
Researchers found PM2.5 from agriculture and wildfires strongly linked to dementia risk, highlighting the dangers of events like the Canadian wildfires polluting air as far away as New York City, and the destructive Maui wildfires, one of the deadliest in US history. It also builds on prior research implicating various pollution sources as potentially influencing dementia risk through pathways like neuroinflammation.
The new study analyzed data on over 27,000 older adults across the US participating in a long-term health survey from 1998-2016. The data comes from the University of Michigan Health and Retirement Study (HRS) which takes a representative sample of more than 20,000 Americans over the age of 50 every two years. Using air pollution statistics and cognitive assessments, the results reinforce PM2.5 exposure as a modifiable population health issue that could meaningfully impact dementia incidence if reduced.
“This level of specificity is new and useful,” said Jonathan W. King, the project scientist for the National Institute on Aging (NIA) who led the study. “As NIA continues to conduct and fund studies on risk factors for dementia, these results will help inform future research, and potentially, policy interventions.”
Real World Implications
While the precise biological mechanisms connecting particulate air pollution to neurodegeneration remain unclear, accumulating evidence suggests that ambient pollution negatively affects the brain. Prior studies have revealed associations between PM2.5 and reduced brain volume, faster cognitive decline, and greater risk for Alzheimer’s dementia and other neurodegenerative disorders.
For example, a 2015 study of over 15,000 older women found that higher PM2.5, especially from vehicle exhaust, was linked to lower white matter volume and worse memory performance over 5-10 years. And a Canadian population study published earlier this year reported that older adults exposed to elevated nitrogen dioxide, a traffic-related pollutant, had a greater risk of developing dementia.
Other research has suggested biological pathways like neuroinflammation triggered by air pollution traveling from the nose to brain regions linked to Alzheimer’s pathology. Autopsy studies have also shown that higher air pollution exposure is associated with greater Alzheimer’s-type biomarker buildup in the brain.
The researchers emphasized the need for comprehensive mitigation policies at all levels of government to effectively combat the threat that bad air poses to brain health.
Some government officials are starting to take such warnings seriously. A Montana judge recently ordered that the state’s Department of Environmental Quality (DEQ) must consider indirect greenhouse gas emissions and climate impacts for proposed projects related to coal, oil, and gas. Her ruling came in response to a lawsuit brought by 16 young Montanans who argued the DEQ was violating state law by failing to consider climate impacts.
After one youth testified that wildfires caused ‘ash to fall from the sky,’ the judge ruled that the plaintiffs possess a ‘fundamental right to a clean and healthful environment.’
The researchers noted other meaningful contributors to poor air quality including vehicle emissions, industrial facilities, power generation, indoor heating and cooking with fossil fuels, certain cleaning chemicals, and ozone. They advised minimizing time outdoors on poor air quality days and using home air filters. However, they added that the onus should not fall solely on individuals.
“As we experience the effects of air pollution from wildfires and other emissions locally and internationally, these findings contribute to the strong evidence needed to best inform health and policy decisions,” said Richard J. Hodes, MD, director of the NIA. “These results are an example of effectively using federally funded research data to help address critical health risks.”