Long-Term Wildfire Smoke Exposure and Increased Risk of Heart Failure in Older Adults.

Background: Fine particulate matter, defined as particles <2.5 μm in diameter (PM), is the most important environmental risk factor for global mortality. Wildfires have been increasing globally, posing a global health challenge. Fire smoke-specific PM is believed to have more cardiovascular toxicity compared with other PM sources; however, the impact of fire smoke PM and heart failure (HF) remains undefined. We sought to investigate the association between long-term exposure to fire smoke PM and HF and compare it with nonfire PM in a large national cohort.

Objectives: This study sought to evaluate the association between long-term exposure to wildfire smoke PM and the risk of incident HF among older adults across the contiguous United States.

Methods: This retrospective cohort study analyzed data from Medicare fee-for-service beneficiaries between 2007 and 2018. We linked individuals to high-resolution exposure estimates of fire smoke and nonfire smoke PM at a 1 × 1-km spatial resolution that were aggregated to ZIP (Zone Improvement Plan) codes by averaging the values of all 1-km grid cells whose centroids fell within each ZIP code boundary and followed them for incident HF. The relationship between PM and incident HF were examined using Cox proportional hazard models, adjusting for individual demographic characteristics and area-level socioeconomic risk factors.

Results: The cohort included approximately 22 million fee-for-service enrollees, with a follow-up totaling 115 million person-years. The mean smoke PM exposure, calculated as the average of all past 2-year moving average exposures across person-years, was 0.51 μg/m. The HR associated with each 1-μg/m increase in the past 2-year average smoke PM was 1.014 (95% CI: 1.007-1.020), which was notably higher than the corresponding HR for nonsmoke PM (1.005; 95% CI: 1.003-1.006). This association corresponds to an estimated 20,238 (95% CI: 10,727-29,612) additional heart failure cases annually among U.S. older adults. Additionally, the number of days exposed to smoke PM exceeding 1 μg/m and 2.5 μg/m over the past 2 years were both significantly associated with an elevated risk of HF. We additionally found that the association between smoke PM and HF was stronger in women, Medicaid-eligible individuals, and those living in lower income areas, indicating higher susceptibility.

Conclusions: In this national cohort, long-term exposure to fire smoke-related PM was linked to a higher risk of HF compared with nonsmoke PM, with greater susceptibility in women and socially vulnerable populations. These findings underscore the need for targeted interventions and policies to reduce wildfire smoke exposure and its cardiovascular impacts.