Breathing in wildfire smoke isn't just bad for the lungs. Researchers have found it's also associated with a higher risk of dementia.
In addition to warmer, drier, more extreme weather, climate change is also causing more active wildfire seasons, and that means more exposure to wildfire smoke. Now, researchers have found that for every extra microgram per cubic meter of smoke, there’s a 21-percent higher risk of developing dementia.
Dr. Holly Elser, a neurology resident at the Hospital of the University of Pennsylvania, presented her research linking wildfire smoke to increased dementia risk at the 2024 Alzheimer’s Association International Conference.
Many of the health risks associated with wildfire smoke come from breathing in tiny toxic particles smaller than 2.5 microns (PM2.5). In previous studies, researchers linked exposure to these particles to the development of asthma or respiratory problems, impaired thinking and executive function, and an increased risk of developing Alzheimer’s and other forms of dementia. But these studies didn’t always differentiate the effects of wildfire smoke pollution from other forms of pollution.
Elser and her colleagues analyzed the electronic health records of more than 1.2 million cognitively healthy Southern Californians aged 60 or older. Combining air quality monitoring data, satellite images, and machine learning techniques, the researchers then determined how much wildfire and non-wildfire PM2.5 each participant was exposed to based on where they lived. They could then see how exposure to these pollutants over three years affected the risk of dementia over the next 12 years.
Researchers controlled for age, sex, race, ethnicity, and other health-related and demographic factors drawn from U.S. census data. Previous studies have shown that Black and Latino, and economically disadvantaged communities are more likely to live and work in areas where they are exposed to higher on-average levels of pollutants.
The researchers found that every one microgram per cubic meter increase of wildfire PM2.5 corresponded to a 21 percent higher risk of developing dementia. For non-wildfire smoke PM2.5, every three microgram per cubic meter increase of pollution was associated with a three percent higher risk of developing dementia.
“We did see evidence that [for] participants in our study who were part of minoritized patient populations or who lived in high poverty census tracts, there was a stronger association between wildfire PM2.5 exposure and dementia,” Elser told Being Patient. Since this analysis included only a subgroup of the study participants, the results are less certain and more research is needed.
But the study findings suggest that the pollutants produced by wildfire smoke may be more harmful even than those produced by other sources such as car exhaust, gasoline, oil, or wood fuel.
There are some theories as to why wildfire smoke might be much worse for the brain than other pollutants: Elser explained that pollutants made under higher temperatures are much smaller: They can get into the brain directly through the nose and have less trouble crossing the blood-brain barrier. There are more neurotoxic particles that make it to the brain and activate the immune cells, called the microglia, causing inflammation and damage to other brain cells.
The chemicals in the wildfire smoke might also play a role. Elser explained that the materials burned to produce wildfire smoke have a higher concentration of chemicals called polycyclic aromatic hydrocarbons which are harmful to health.
How to protect your brain from wildfire smoke
For an individual, even a 10 to 20 percent increase in dementia risk may not be huge: the average person over 65 might have a two-percent chance of being diagnosed with Alzheimer’s in a given year, and so a 20 percent increase would bump up that risk to 2.4 percent. But across the U.S., these small increases leave a mark — previous studies estimate that PM2.5 exposure is responsible for as many as 188,000 new cases of Alzheimer’s and related dementias each year.
Elser and her colleagues recommend that people update their air filtration systems and check the air quality index (AQI) on a weather app. An AQ1 of 100 or higher means that the air is unhealthy to breathe. If you must go outside when the air quality is 100 or higher, minimize how much time you spend outside; if you must go outside, wear an N95 mask or P100 respirator; and close the windows in your house.
“We know [these prevention methods] are going to be more challenging for people from lower socioeconomic status situations,” said Maria C. Carrillo, the chief science officer and medical affairs lead of the Alzheimer’s Association. “They may have outside jobs, and they may have no choice around being outside on days when the air quality index is over 100.”
In addition, Carrillo said, people who rent their homes may have little control over the air filtration in their apartments: If you can’t afford masks, respirators, or air purifiers, check for a local Mask Bloc. These organizations sprouted during the COVID-19 pandemic and provide free gear to local communities. Another option involves building your own DIY air filter called a Corsi-Rosenthal box, which can filter out wildfire pollutants. Instructions for building these boxes are available online.
