Wildfires and Dementia

It's wildfire season here in the Pacific Northwest.  There were recent reports of as many as 200 fires burning, but we've actually had relatively minimal smoke where we live in south central Washington State.  Not like 2017.  That was bad.  After being unexpectedly stranded on the East Coast last week for four days (due to that computer hiccup you heard about), we flew home above the smoke.  I could see it out the window of the airplane.  It was there.

We wrote previously about how air pollution promotes Alzheimer's disease.  Tiny particles in the air can pass along the path of the olfactory nerve into the brain, bypassing the blood-brain barrier.  The particles then promote the disease.  Therefore, we find higher incidences of Alzheimer's disease among people who live near freeways.  Car exhaust includes many of these particles, classified as PM2.5.

But what's worse than car exhaust?  Apparently, it's wildfire smoke.  According to new research presented at the Alzheimer's Association International Conference (currently in progress in Philadelphia), the PM2.5 particles from wildfire smoke are significantly more likely to cause dementia than particles from other sources.

So what did the researchers do?  They reviewed and analyzed health records of more than 1.2 million customers of Kaiser Permanente in southern California, 60 years or older between 2009-2019.  None of them had been diagnosed with dementia at the beginning of the study.  They estimated total PM2.5 exposure from various sources, including satellite-derived aerosol properties and Environmental Protection Agency monitoring.  They used air quality monitoring data, satellite imagery, and machine learning techniques to separate wildfire and non-wildfire exposure to PM2.5 particulates.  The researchers determined each study participant’s exposure to both sources of PM2.5 according to where they lived. They compared that information to subsequent diagnoses of dementia in participants’ health records. 

So what did they find?  The researchers observed a 21% increase in the odds of dementia diagnosis for every increase of 1 microgram of particulate matter per cubic meter ( µg/m3) of air in a three-year average wildfire PM2.5 exposure.  They determined that the study population had a 3% increased risk of dementia diagnosis for every increase of 3 µg/m3 in the three-year average of non-wildfire PM2.5 exposure.  

If I'm reading this right, and the relationships are linear, that implies that a 1 micro-gram per cubic meter increase in PM2.5 particulates from wildfire smoke increases your risk of dementia by by a factor of 21 times over other sources!  That's a huge difference!

From the Alzheimer's Association press release: “Previous research has found that exposure to PM2.5 is associated with dementia, but in light of our large, long-term study, its apparent the risk from exposure due to wildfire smoke is an even bigger concern,” said Holly Elser, M.D., Ph.D., the study’s first author and a neurology resident at the Hospital of the University of Pennsylvania, Philadelphia. “Air pollution produced by wildfires now accounts for more than 70% of total PM2.5 exposure on poor air quality days in California. This is a real problem.” 

Why would this be?  The press release further quotes Dr. Elsner:  "[In wildfire smoke], PM2.5 are produced at higher temperatures, contain a greater concentration of toxic chemicals and, on average, are smaller in diameter than PM2.5 from other sources."  She said more research needs to be done to determine the exact mechanisms.

So ... check the air filters in you home system.  Mine has a bluetooth signal to my cell phone to tell me when it's time to change a filter.  An Air Quality Index (AQI) number of 100 or higher means the air is unhealthy to breathe. To reduce their risk when the AQI is 100 or higher, it's recommended that people stay inside when possible and close the windows.  (Fires or no fires, our AQI here today is 23.  The sun is shining brightly, and the sky is very blue.)