Impact of Extreme Heat and Wildfire Smoke on Life Expectancy

Extreme heat, wildfires, and other natural disasters have led to acute effects on morbidity and mortality; yet, the long-term consequences of extreme heat and wildfires have been sparsely studied. This is due in part to the paucity of studies with longitudinal information on individual- and area-level factors along with fine-scale weather and wildfire data. There is an urgent need to investigate the long-term consequences of extreme heat and wildfires in well-designed studies that include a comprehensive assessment of these exposures and their independent and joint effects on life expectancy, coupled with a critical evaluation of possible mediators (ambient particulate matter) and moderators (sociodemographics, comorbidities, health behaviors, area-level factors, and geography). Furthermore, the biological processes by which extreme heat and wildfire affect mortality are not well understood. While evidence of the impact of particulate matter on DNA methylation as a measure of epigenetic regulation is accumulating, studies of extreme heat and DNA methylation are sparse. Elucidation of the underlying pathways and the identification of interventions for high-risk groups are needed. To address these gaps, we will conduct a rigorous investigation of the impacts of extreme heat and wildfire smoke on adult life expectancy, leveraging the unique epidemiological resources of the Multiethnic Cohort Study, a large population-based study that includes 112,000 adult men and women from California, who were ages 45-75 at enrollment in 1993-1996 and currently ages 72-103. Specifically, we will generate and characterize extreme heat and wildfire smoke for California Multiethnic Cohort participants spanning a 24-year period (Aim 1); assess the impacts of long-term exposures of extreme heat and wildfire smoke on life expectancy (Aim 2); and DNA methylation and epigenetic age (Aim 3). The strengths of this proposal include: 1) the use of state-of-the-art exposure assessment methods to characterize extreme heat, wildfire smoke, and particulate matter; 2) a large population-based sample with detailed individual- and area-level data with sufficient power to detect modest effects that are broadly generalizable to similar population groups in the US; 3) the assessment of the role of biological pathways (DNA methylation) by which extreme heat and wildfire smoke may operate; and 4) a thorough investigation of effect modification by a variety of factors such as greenspace and cooling centers as well as the mediation of effects by particulate matter. Findings from this proposal will expand our understanding of the contribution of long-term extreme heat and wildfire smoke on life expectancy. This knowledge has translational relevance in providing empirical evidence for implementation scientists to develop strategic interventions and response plans to combat the health effects of extreme heat and wildfire smoke.