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_2.5), is the most important environmental risk factor for global mortality. Wildfires have been increasing globally, posing a global health challenge. Fire smoke–specific PM_2.5 is believed to have more cardiovascular toxicity compared with other PM_2.5 sources; however, the impact of fire smoke PM_2.5 and heart failure (HF) remains undefined. We sought to investigate the association between long-term exposure to fire smoke PM_2.5 and HF and compare it with nonfire PM_2.5 in a large national cohort. Objectives: This study sought to evaluate the association between long-term exposure to wildfire smoke PM_2.5 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_2.5 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_2.5 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_2.5 exposure, calculated as the average of all past 2-year moving average exposures across person-years, was 0.51 μg/m³. The HR associated with each 1-μg/m³ increase in the past 2-year average smoke PM_2.5 was 1.014 (95% CI: 1.007-1.020), which was notably higher than the corresponding HR for nonsmoke PM_2.5 (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_2.5 exceeding 1 μg/m³ and 2.5 μg/m³ over the past 2 years were both significantly associated with an elevated risk of HF. We additionally found that the association between smoke PM_2.5 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_2.5 was linked to a higher risk of HF compared with nonsmoke PM_2.5, 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.