Ambient outdoor heat and accelerated epigenetic aging among older adults in the US.

Extreme heat is well-documented to adversely affect health and mortality, but its link to biological aging-a precursor of the morbidity and mortality process-remains unclear. This study examines the association between ambient outdoor heat and epigenetic aging in a nationally representative sample of US adults aged 56+ ( = 3686). The number of heat days in neighborhoods is calculated using the heat index, covering time windows from the day of blood collection to 6 years prior. Multilevel regression models are used to predict PCPhenoAge acceleration, PCGrimAge acceleration, and DunedinPACE. More heat days over short- and mid-term windows are associated with increased PCPhenoAge acceleration (e.g., : 1.07 years). Longer-term heat is associated with all clocks (e.g., : 2.48 years for PCPhenoAge, : 1.09 year for PCGrimAge, and : 0.05 years for DunedinPACE). Subgroup analyses show no strong evidence for increased vulnerability by sociodemographic factors. These findings provide insights into the biological underpinnings linking heat to aging-related morbidity and mortality risks.