Short-term spikes in wildfire smoke during the 2023 Canadian wildfires were linked to higher stroke rates and more severe strokes in New Jersey, a preliminary study suggests.
Researchers used a stroke registry to identify strokes recorded in June and July 2023 and compared them with strokes during the same months a year earlier.
They reviewed US Environmental Protection Agency data from air quality monitors in Camden, New Jersey.
Study author Elizabeth Cerceo, MD, of Cooper Medical School of Rowan University in Camden, New Jersey, said: “Wildfire smoke contains pollutants like ozone and particulate matter, so it is more than a nuisance, it can be a public health hazard.
“The 2023 Canadian wildfires resulted in unprecedented declines in air quality across the northeastern United States.
“Our findings show that short-term exposure to elevated air pollution from these wildfires was associated with a higher incidence and severity of stroke.”
Researchers measured ozone, a gas that can irritate the lungs and worsen breathing conditions such as asthma, and fine particulate matter known as PM2.5, tiny airborne particles small enough to enter the lungs and bloodstream.
During the wildfires, ozone levels peaked at 136 parts per billion compared with a median concentration of 36 parts per billion.
Fine particulate matter reached 211 micrograms per cubic metre compared with a median of 48.5 micrograms per cubic metre.
Daily air quality data was matched with the timing of each stroke.
Because pollution effects may take several days to affect the body, researchers also considered pollution levels from the one to two days before each stroke.
Researchers found that on days when ozone levels were above average, the stroke rate was 1.25 cases per day compared with 0.93 per day on days with below-average ozone.
After adjusting for factors including age, sex, race and cause of stroke, higher average ozone days were associated with 0.32 more strokes per day.
Above-average ozone days were also linked to a higher proportion of bleeding strokes, which occur when a blood vessel in the brain ruptures and are often more severe than ischaemic strokes, the most common type caused by a blocked artery.
Higher particulate matter levels were also associated with longer hospital stays and more severe strokes.
Cerceo said: “While longer-term air pollution has been recognised as a risk factor for stroke, less is known about short exposures to wildfire smoke.
“Our study addresses a critical gap by providing more information about the neurological impact of wildfire smoke.
“Our findings can help guide stroke prevention and underscore the need for public health interventions during wildfires.”
Cerceo noted the analysis focused on a short wildfire period and represents an early signal rather than a complete picture of the association between wildfire smoke and stroke risk.
The study does not show that wildfire smoke directly causes or worsen stroke, only that an association was observed.
One limitation was that the study used daily average pollution measurements. More detailed hourly measurements may also affect strokes but may not be reflected in averages.
Other weather factors such as humidity and barometric pressure were not included. Future research will examine longer time periods.
