- Long-term exposure to wildfire smoke may increase the risk of being diagnosed with dementia, new research suggests.
- The risk of dementia diagnosis was higher for wildfire smoke than for other types of air pollution, such as that emitted by motor vehicles and factories.
- Experts recommended reducing your risk by using air filters at home and wearing a high quality mask when going outside during poor air quality days.
Wildfires can be devastating for communities and natural ecosystems. But wildfire smoke also poses a direct threat to human health, damaging not only the heart and lungs but also the brain.
New research suggests that when it comes to brain health, wildfire smoke may even be more harmful than other types of air pollution.
In a preliminary study reported on July 29 at the Alzheimer’s Association International Conference in Philadelphia, scientists found that long-term exposure to wildfire smoke increases the risk of being diagnosed with dementia.
The risk was higher for exposure to wildfire smoke than for other types of air pollution, such as pollution emitted by motor vehicles and factories.
This study “adds to the evidence that not only does [wildfire smoke] pose a risk to our long-term cognitive health, but it may also be more dangerous to our health than [fine particulate matter] from other sources,” said Stephanie Cleland, PhD, MSPH, assistant professor in the Faculty of Health Sciences at Simon Fraser University, who was not involved in the new research.
Last year, Canada experienced the highest wildfire carbon emissions on record, and Greece experienced the largest wildfire to date in the European Union. The fires in Canada led to poor air quality alerts in many parts of the United States.
As human-driven climate change causes wildfires to grow more intense and destructive, wildfire smoke will become a problem for more people, with longer-term impacts.
“A lot of research on wildfire smoke has focused on short-term exposure because we previously viewed it as an intermittent, infrequent occurrence,” said Cleland.
“But with climate change playing a role in drying out forests, reducing snow levels, and increasing temperatures, we’re seeing an increase in the frequency and intensity of wildfires, and as a result, an increase in wildfire smoke,” she said.
“This study shows that it’s not just your exposure during the one week that it’s smoky [that matters for your health],” she said. “It’s your exposure over years of wildfire smoke, especially if you live in places like California, Washington, Oregon, or British Columbia that have frequent wildfires.”
Dementia risk of wildfire smoke: what’s the connection
Wildfire smoke contains a type of air pollution known as fine particulate matter (also known as PM2.5). This mixture contains solid and liquid droplets that are 2.5 microns or smaller in diameter — 20 to 30 times smaller than the width of an average human hair.
Air pollution emitted by motor vehicles and factories also contains fine particulate matter.
Because of their small size, these small particles can travel deep into the lungs — and may enter the bloodstream — where they can affect the lungs and heart.
A growing number of studies suggest that fine particulate matter may also affect the brain, resulting in an increased risk of dementia, stroke, and headache.
Research by Cleland and her colleagues, published in 2022 in Environmental Health Perspectives, even found that short-term exposure to wildfire smoke may lead to decreases in certain types of cognitive function, such as attention.
In the new study, researchers examined the health records of over 1.2 million members of the Kaiser Permanente health system in southern California. Between 2009 and 2019, members were 60 years or older. None had been diagnosed with dementia at the beginning of the study.
Researchers used air quality monitoring data and satellite imagery to estimate members’ exposure to fine particulate matter based on where they lived. They also looked separately at levels of wildfire and non-wildfire fine particulate matter.
People with greater exposure to wildfire smoke were more likely to be diagnosed with dementia, researchers found.
The risk of a dementia diagnosis increased by 21% for every increase of 1 microgram per cubic meter in the three-year average wildfire-related fine particulate matter exposure.
In contrast, for other types of fine particulate matter exposure, the risk of dementia diagnosis increased 3% for every increase of 3 micrograms per cubic meter in the three-year average fine particulate matter exposure.
The new study has not been published yet in a peer-reviewed journal, so the results should be viewed with caution.
Some communities are impacted more
For their analysis, researchers took into account many factors that might affect the results, such as age, sex, cigarette smoking, and the poverty level of the neighborhood. This and the large number of people included are strengths of the study.
However, while “the study accounted for as many factors as they could in the Kaiser database [that might affect the results], there are likely other environmental factors not captured in their data set,” said Keith Vossel, MD, director of the Mary S. Easton Center for Alzheimer’s Research and Care at UCLA, who was not involved in the research.
For example, “it is unclear how many individuals wore protective masks when wildfires were occurring,” he told Healthline.
The results of the new study also showed that people from racial and ethnic minorities and those living in high-poverty areas appeared to be more impacted by wildfire smoke.
Cleland said this fits with other research on air pollution, in general, which has found that people living in more disadvantaged areas or who have less access to resources tend to have a higher risk of health problems related to air pollution.
In terms of exposure to wildfire smoke, people living in communities at higher risk may live in homes that have less high quality air filtration, or they may not have access to other indoor spaces with clean air, she said.
Lilah Besser, Phd, MSPH, a research assistant professor at the Miller School of Medicine, Comprehensive Center for Brain Health, said the results of the new study are in line with earlier research showing a connection between exposure to fine particulate matter and a risk of dementia.
“This study adds to that body of research by suggesting an even greater risk of dementia among those exposed to wildfire (versus non-wildfire) PM2.5 exposure,” she told Healthline.
However, researchers estimated people’s exposure to fine particulate matter, which may not always be accurate. Future research should measure people’s actual exposure to wildfire smoke and other types of air pollution, said Besser, who was not involved in the new research.
In addition, researchers should “investigate the components of wildfire smoke other than PM2.5 that may be the root cause of the amplified dementia risk,” she said.
Study author Holly Elser, MD, PhD, a neurology resident at the Hospital of the University of Pennsylvania, Philadelphia, said in a news release that wildfire smoke may be more harmful to the brain because fine particulate matter from wildfires is produced at higher temperatures, contains higher amounts of toxic chemicals and has smaller particles.
How to reduce health risks from wildfire smoke
Cleland said there are several things people can do to protect their health from wildfire smoke. These will also protect you from other sources of air pollution.
“First, check the local air quality where you live,” she said. “That can help you make informed decisions.”
If the air quality is at a dangerous level, you might want to avoid going outside, she said, or if you do have to leave your home, wear a high-quality respirator like an N95 mask.
Another thing people can do is create a safe space indoors.
“If you’re able to, seal the doors and windows and run an air cleaner. That’s going to create a space in which, even if it’s smoky outside, you have clean, safe air to breathe,” she said.
High-efficiency particulate air (HEPA) purifiers can filter smoke, dander, and pollen from the air. Commercial devices are available, but you can also build an air filter using four high-quality filters and a box fan. One of the most popular DIY air purifiers is the Corsi-Rosenthal box.
If you don’t have access to an air purifier for your home, “public spaces, like malls, libraries or community centers often have built-in high-filtration air systems,” said Cleland. “So accessing those spaces during smoky periods can be a good way to reduce your exposure.”
Besser said community strategies are also needed to reduce the risk of exposure among the most vulnerable populations.
“This could include local agency strategies such as N95 mask distribution and educational efforts to community organizations about Air Quality Index (AQI) alerts and the risks of air pollution,” she said.
Takeaway
Researchers examined the health records of over 1.2 million members of the Kaiser Permanente health system. They also used air quality monitoring data and satellite imagery to estimate members’ exposure to fine particulate matter in wildfire smoke and other sources.
Fine particulate matter, also known as PM2.5, is small enough to travel deep into the lungs and may enter the bloodstream. Research shows that this type of pollution, which is also emitted by motor vehicles and factories, can damage the lungs, heart, and brain.
In the study, people who were exposed to greater levels of wildfire smoke had a higher risk of being diagnosed with dementia. This risk was even higher than that caused by exposure to non-wildfire sources of pollution.
