Long-term exposure to wildfire smoke associated with increased risk of dementia: study

Being exposed to wildfire smoke over a long period of time could increase the risk of developing dementia even more than exposure to other sources of air pollution, according to new research.

In the study, published last week in the journal JAMA Neurology, researchers looked at a cohort of more than 1.2 million people over the age of 60 living in Southern California between 2008 and 2019. They tracked dementia incidence among the cohort and compared it to the average concentration of fine particulate matter, also known as PM2.5, in the air due to wildfires in the region.

They found that when the three-year average concentration of wildfire PM2.5 went up by just one microgram per cubic metre of air, there was an associated 18 per cent increase in the odds of a dementia diagnosis.

The same increase in concentration of non-wildfire PM2.5 was associated with only a three per cent increase in the odds of a dementia diagnosis.

Although previous research has connected long-term exposure to air pollution with a greater risk of dementia, less research has been done into the effect of specific air pollution sources.

"They're seeing a stronger effect of PM2.5 from wildfires than from other sources," said Scott Weichenthal, an associate professor in the department of epidemiology, biostatistics and occupational health at McGill University in Montreal. He was not involved in the study.

"That's important because we need to start paying more attention to the kinds of particles that are in the air, not just how much mass is in the air, because the chemical composition also plays a really important role in the health effects."

Fine particulate matter are tiny particles in the air found in smoke and fumes that measure less than 2.5 micrometres and can travel deep into the lungs when inhaled.

Wildfire smoke can contain a dangerous cocktail of chemicals from burned residences, vehicles and plastics, Weichenthal said. And unlike smog, which is a steady source of air pollution, wildfire smoke brings massive spikes of PM2.5 concentration in the air — which can affect not only the lungs but the entire body.

When the body encounters foreign particles, it mounts a response, sending the lungs into a "heightened state of inflammation" that can spill over into other organs through inflammatory cells in the bloodstream, said Michael Brauer, a professor at the school of population and public health at the University of British Columbia in Vancouver.

This is the leading theory for how long-term exposure to air pollution can impact the brain, he told CBC News, although scientists aren't yet certain about the mechanisms.

Brauer, who was not part of the study but has previously examined the connection between PM2.5 and dementia in his research, said air pollution strongly impacts the cardiovascular system, potentially affecting blood flow to the brain as well.

Many Canadians live in areas where wildfires are simply a reality of life. So how can you protect yourself?

Air filtration systems, such as HEPA filters, go a long way in cutting down long-term exposure, Weichenthal said. On days when the air quality is poor during wildfire season, wearing a KN95 or N95 mask will also minimize risk when outdoors.