What does this research mean for the field?

Chronic exposure to wildfire smoke PM2.5 increases the risk of incident stroke in older adults. Novelty: ClaimNovelty.INCREMENTAL. Consensus alignment: ConsensusAlignment.NEUTRAL.

March 3, 2026

Long-term exposure to wildfire smoke particulate matter and incident stroke: a US nationwide study

Key Result

Chronic exposure to wildfire smoke PM2.5 increases the risk of incident stroke in older adults.

Key Points

Long-term exposure to wildfire smoke PM2.5 significantly increases stroke risk among older adults.
Among ∼25 million beneficiaries, ∼2.9 million incident stroke cases occurred during the study.
A national open cohort study utilizing machine learning models estimated smoke-specific PM2.5 exposure levels over time for participants aged ≥65 years from 2007 to 2018. The analysis employed Cox proportional hazards models to assess stroke risks per unit increase in PM2.5 exposure, indicating stronger associations with wildfire smoke exposure. Supports policy interventions to reduce exposure to wildfire smoke, particularly among older and vulnerable populations.

Structured PICO

Does chronic exposure to wildfire smoke PM2.5 increase the risk of incident stroke in older adults?

Population

Older adults in the United States

Intervention

Chronic exposure to wildfire smoke particulate matter (PM2.5)

Outcome

Incident strokehard clinical

Long-term exposure to wildfire smoke PM2.5 is associated with an increased risk of incident stroke in older adults, highlighting the need for public health policies to reduce exposure.

Main Result

Absolute Event Rate: 0% vs 0%

Abstract

BACKGROUND AND AIMS: Wildfire smoke is a growing public health concern, particularly due to its high fine particulate matter (PM2.5) concentrations. While short-term exposure has been linked to adverse cardiovascular outcomes, long-term effects remain understudied. This study examined the association between long-term wildfire smoke PM2.5 exposure and incident stroke among older US adults. METHODS: A national open cohort study was conducted among Medicare Fee-for-Service beneficiaries aged ≥65 years from 2007 to 2018. Stroke cases were identified using validated Medicare claims. Wildfire smoke PM2.5 exposure was estimated at a 1 km2 resolution using a machine learning model distinguishing smoke-specific PM2.5 from other ambient sources. Stratified Cox proportional hazards models with generalized estimating equations were used to estimate hazard ratios (HRs) per 1 µg/m3 increase in wildfire smoke PM2.5, adjusting for non-smoke PM2.5, meteorological variables, socio-economic status, and healthcare capacity. RESULTS: Among ∼25 million beneficiaries, ∼2.9 million incident stroke cases occurred. Long-term wildfire smoke PM2.5 exposure was significantly associated with increased stroke risk. Stronger associations were observed for longer exposure windows. For instance, per 1 µg/m3 increase in 3-year average wildfire smoke PM2.5 was associated with a 1.3% increase in stroke risk (HR: 1.013; 95% CI: 1.006, 1.020). Associations for wildfire smoke PM2.5 were generally stronger than for non-smoke PM2.5 per unit exposure. CONCLUSIONS: This study provides national-scale evidence that chronic exposure to wildfire smoke PM2.5 increases stroke risk in older adults. These findings underscore the long-term health risks of wildfire smoke and support policies aimed at reducing exposure, especially among vulnerable populations.