A recent study conducted by researchers from the University of Michigan suggests that individuals who regularly inhale smoke from wildfires are at a higher risk of developing dementia. The study focuses on particulate matter, known as PM2.5, which refers to tiny particles that are released from fires, as well as the use of pesticides and herbicides in agricultural production. These particles are so small that they are invisible to the naked eye, and when inhaled, they can cause inflammation and be absorbed into the body.
The study highlights the increasing prevalence of wildfires, such as those in Hawaii and New York this year, and how rising temperatures contribute to their occurrence. The maps provided depict PM2.5 concentrations in the US in 2017 and Alzheimer’s rates by county in 2020 to illustrate the correlation.
Although the researchers couldn’t definitively prove that the pollution measured directly caused dementia, previous studies have shown that PM2.5 can enter the bloodstream from the lungs and potentially damage blood vessels in the brain, increasing the risk of the disease. Additionally, studies conducted on mice have indicated that pollution can lead to an increased production of beta amyloid proteins, which are associated with dementia.
While levels of PM2.5 in the US have been declining since 2000 thanks to increased awareness and the use of cleaner fuel, cities and some agricultural areas still experience high pollution levels. The safe limit for PM2.5 is set at 12ug/m3, but cities like San Francisco, New York, and St. Louis regularly surpass this limit. Earlier this year, smog from Canadian wildfires made New York one of the most polluted cities in the world.
To conduct the study, researchers analyzed data from the Environmental Predictors of Cognitive Health and Aging study, which tracks environmental exposures and cognitive diseases among tens of thousands of adults. Using a nationally-representative sample of 27,857 participants over the age of 50 who did not have dementia at the start of the study, the researchers compared the distribution of dementia cases to PM2.5 levels in 2017.
Controlling for factors like sex, ethnicity, education, and primary residence, the researchers found that agriculture and vehicle emissions had the highest association with an increased risk of dementia. Specifically, for every increase in PM2.5 levels from agriculture, the risk of developing dementia rose by 13 percent. Wildfire smoke was associated with a five percent increase in risk, while road traffic fumes contributed to a six percent increase. The association with other sources, such as non-coal energy and windblown dust, was minimal or absent.
Although the study’s observational nature doesn’t allow for a direct causal link between fumes and dementia, the researchers believe that the neurotoxic pesticides and herbicides used in agriculture and the release of highly toxic particles from burning natural and synthetic materials may contribute to the increased risk.
In a secondary analysis, the researchers estimated that pollution could potentially account for up to 188,000 new dementia cases annually. Wildfire smoke was found to be responsible for up to 25 percent of average PM2.5 concentrations across the US and up to 50 percent in certain western regions.
While some experts caution that the findings linking pollution sources to dementia are not conclusive, the study provides valuable support for previous research indicating the adverse effects of PM2.5 on cognitive function and the potential acceleration of dementia onset.
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