Short-term surges in air pollution in the US state of New Jersey—caused by the 2023 Canadian wildfires—have been linked to a higher stroke rate as well as an increased incidence of haemorrhagic strokes, according to a newly released preliminary study.
“Wildfire smoke contains pollutants like ozone and particulate matter, so it is more than a nuisance; it can be a public health hazard,” said study author Elizabeth Cerceo (Cooper Medical School of Rowan University, Camden, USA). “The 2023 Canadian wildfires resulted in unprecedented declines in air quality across the northeastern USA. Our findings show that short-term exposure to elevated air pollution from these wildfires was associated with a higher incidence and severity of stroke.”
For the study, researchers used a stroke registry to identify all cases of stroke—ischaemic and haemorrhagic—that occurred during June and July 2023, and during the same months a year earlier. They reviewed US Environmental Protection Agency data for both periods from air quality monitors located in Camden, New Jersey, and calculated average daily exposures for ozone—which, when inhaled, can cause shortness of breath, coughing and aggravation of conditions like asthma. They also calculated daily average exposures to air pollution for particles with a diameter of 2.5 micrometres or less (PM2.5).
Ozone levels peaked at 136 parts per billion (ppb) during the wildfires in 2023 compared to a median ozone concentration of 36ppb, while particulate matter reached 211 micrograms per cubic metre (µg/m3) compared to a median concentration of 48.5µg/m3.
The researchers relay that daily air quality data was matched with the timing of each stroke—and, because pollution effects may take a few days to impact the body, they also took into account the levels from the preceding 1–2 days before participants had their stroke. Some 72% of days had an ozone concentration that was equal to or less than the World Health Organization (WHO)-recommended level of 50ppb, while 28% of days exceeded this level.
Analyses of 42 strokes that occurred on above-average ozone-level days versus 80 strokes that occurred on below-average days revealed that the stroke incidence—the rate at which new stroke cases occurred—was 1.25 per day across the above-average days compared to 0.93 per day across the below-average days. After adjusting for factors like age, sex, race, and cause of stroke, the researchers ultimately found that the days with higher average ozone levels were associated with an increase of 0.32 in daily stroke incidence.
Furthermore, the researchers share that—when looking at strokes on above-average ozone days—there was a higher proportion of haemorrhagic strokes as well as a greater proportion of strokes caused by large-artery atherosclerosis.
For particulate matter levels, 38% of days were found to be above average and 62% were below average. The researchers compared 39 strokes that occurred on above-average particulate-matter days versus 83 strokes that occurred on below-average days, and discovered that heightened levels of particulate matter were associated with longer hospital stays and higher scores on a stroke-severity scale.
“While longer-term air pollution has been recognised as a risk factor for stroke, less is known about short exposures to wildfire smoke,” Cerceo commented. “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 also noted, however, that this analysis focused on a short period of time, meaning the findings represent an early signal as opposed to a complete picture of the association between wildfire smoke and risk of stroke. Future research will look at longer periods of time, she added.
The researchers concede that the fact they looked at daily average pollutants represents a limitation of the present study too, with Cerceo stating that more nuanced, hourly measurements could impact strokes but may not be reflected within these averages. Similarly, other weather variables like humidity and barometric pressure were not incorporated into the researchers’ analyses.
These findings are set to be presented next month at the 2026 American Academy of Neurology (AAN) annual meeting (18–22 April, Chicago, USA).
