Short-term spikes in air pollution in New Jersey caused by the 2023 Canadian wildfires were associated with a higher incidence of stroke and stroke severity, preliminary research results suggested.

“We know that particulate matter air pollution and other forms of air pollution are associated with dementia and Parkinson’s disease, and so it wasn’t surprising that we saw this with stroke as well,” study investigator Elizabeth Cerceo, MD, of Cooper Medical School of Rowan University in Camden, New Jersey, told Medscape Medical News. 

The study’s preliminary findings will be presented at the American Academy of Neurology Annual Meeting in April.

No Safe Level

Air pollution is an established risk factor for cerebrovascular disease and may contribute to stroke by increasing oxidative stress, impairing blood vessel function, and triggering systemic inflammation that can lead to ischemic or hemorrhagic events.

There is “no safe level” of air pollution and the 2023 Canadian wildfires resulted in “unprecedented” declines in air quality across the northeastern US, Cerceo told Medscape Medical News. 

Using the Cooper Observational Acute Stroke and Thrombectomy Registry, her team examined all ischemic and hemorrhagic strokes that occurred during June and July of 2023 (the wildfire smoke period) and compared them with cases from the same months in 2022.

They obtained daily average ozone and PM_2.5 levels from Environmental Protection Agency air quality monitors in Camden, New Jersey. They matched daily pollution levels with the timing of each stroke and also considered pollution levels in the 1-2 days before the event to account for lag effects.

During the 2023 wildfire smoke period, ozone levels in Camden peaked at 136 parts per billion (ppb) — a huge increase compared with a typical median level of 36 ppb.

Of a total of122 strokes analyzed, 80 occurred on below average ozone days and 42 occurred on above average ozone days.

Higher ozone levels correlated with greater stroke incidence (P = .016). On higher-ozone days, the incidence of stroke was 1.25 per day compared with 0.93 per day on lower-ozone days.

Higher ozone levels also correlated with a higher proportion of hemorrhagic strokes (P = .027) and more cases related to large artery atherosclerosis (P = .028). In addition, higher levels of PM_2.5 were associated with worse outcomes.

During the 2023 wildfires, levels of PM_2.5 in Camden reached 211 µg/m³ compared with a median of 48.5 µg/m³. The researchers compared 39 strokes that occurred on above average PM_2.5 days to 83 strokes that occurred on below average PM_2.5 days.

They found that strokes occurring on above average PM_2.5 days were associated with higher scores on a standard stroke severity scale (P = .035) and longer hospital stays (P = .032).

National Health Crisis

Reached for comment, Mitchell Elkind, MD, MS, chief science officer, Brain Health & Stroke, American Heart Association, described the findings as “a wake-up call.” 

“While it’s been known for at least a decade that both short-term and chronic air pollution raise stroke risk, the clear link between acute wildfire smoke exposure from distant sites and stroke risk, and the impact on stroke severity is striking,” said Elkind who wasn’t involved in the study.

“This underscores how even short-term surges in wildfire smoke and air pollution crossing borders, can have immediate, serious neurological effects,” he added.

Yaguang Wei, PhD, assistant professor of environmental medicine at Icahn School of Medicine at Mount Sinai in New York City, who also wasn’t involved in the research, noted that wildfire activity has increased in intensity, frequency, and season length in recent decades, and is reversing previous improvements in US air quality.”

Wei noted that this research is “an important regional contribution” to the literature — one that emphasizes the fact that wildfire smoke is “not just a local issue” where fires occur, but a “national health crisis.”

He noted that wildfire smoke PM2.5 is considered more toxic to humans than nonsmoke PM_2.5 due to its higher contents of carbonaceous and polar organic compounds, which can lead to respiratory illness, cardiovascular disease, neurologic disease, and premature death.

In a recent study, Wei and his colleagues found that wildfire smoke PM_2.5 was responsible for ~24,100 all-cause deaths per year in the contiguous US.

Of note, the exposure-response curve for all-cause mortality increased monotonically, with no evidence of a “safe” threshold. And among six cause-specific outcomes studied, mortality from neurologic disease showed the greatest increase per 0.1 μg/m³ increase in smoke PM_2.5 exposure.

Cerceo said she now counsels all of her patients to download the AirNow.gov app to be aware of air quality in their area.

“Patients can’t necessarily control the air quality right outside their window, but they can do things to try to keep themselves safe — like trying not to go out at peak times when the air pollution is really bad,” she said.

Another helpful tool is the OSHA NIOSH heat safety app, which allows people to monitor, the heat index and risk levels for a specific location in real-time so they can plan outdoor activities accordingly, she said.

This study had no commercial funding. Cerceo and Wei had no relevant conflicts of interest.