Air pollution in major Canadian cities linked to poorer brain health: study

Sandi Azab, lead author on study that links air pollution to poorer brain function.

While Canada is considered to have a good level of outdoor air quality compared to other parts of the world, a study out of McMaster University suggests a link between air pollution in urban Canadian centres and weaker brain health in adults.

The study, published this month online in the journal Stroke, focuses on a link between low levels of air pollutants across several major Canadian cities, and preclinical cognitive outcomes.

It found that people who live in regions that have more air pollution faired worse on cognitive tests that looked at memory, understanding and mental speed.

Lead author Sandi Azab said that while it’s known that air pollution is a risk factor for dementia, the research team wanted to examine a different angle.

“Our motivation was to test in a very low setting of air pollutants, such as Canada,” she told CTV News. “Is there a link between common pollutants at these low levels and what we call preclinical outcomes, or very subtle measures of cognitive function?”

The study analyzed data from around 7,000 adults from Hamilton, London, Ont., Toronto, Calgary, Vancouver, Ottawa, Montreal, and Halifax, between the ages of 32 and 81, with the medium age of 57.6.

The researchers linked air pollutants for an average of 5 years to where the participants lived. Throughout a four year window, they tested their cognitive functions, using routine tests on brain performance. They also looked at “silent” changes to the brain using MRI – subtle damage to the brain that’s not necessarily symptomatic.

They found that two major pollutants – fine particulate matter known as PM2.5 and nitrogen dioxide – were associated with lower scores of brain function on two different brain tests. One measured things like memory, recall and language, while the other was a non-language-specific test that measured processing speed – how fast the brain works.

“We found statistically significant, subtle yet important lower scores on these two tests associated with exposures to the two pollutants,” Azab said.

Those who were exposed to higher levels of pollutants, scored slightly lower than those who were exposed to lower levels.

The researchers also wanted to translate what that would look like in terms of aging. They found that every five-microgram per cubic meter increase of exposure to PM2.5 was associated with lower scores similar to about two to 12 years of aging.

Tougher environmental and clinical regulations could help

Azab said she hopes the findings will have an encouraging message, rather than a discouraging one.

“We’re very fortunate that we are living in Canada with very clean air, relatively,” she said. “But I think there are disparities or differences between the different cities.”

She said tighter regulations on pollutants from a policy level, as well as more targeted screenings on a clinical level could be beneficial to Canadians.

“If we know that there are certain populations at a higher cardiovascular risk, so these could benefit from an assessment of their air pollution exposure,” she said “There are some studies recommending that, and mostly at the primary care level, no one asks the patient about your air pollution exposure.”

Additionally, Abaz said to further reduce exposure to pollutants, it’s important to stay inside when there is wildfire smoke in the atmosphere – a main source of PM2.5 – and for vulnerable populations to reduce their risk of exposure by wearing a tight fitted mask outside on days of poor air quality.