Whole-blood DNA-methylation patterns during portable-sauna use in firefighters: an exploratory, single-arm pilot study

Research in model organisms has consistently shown that mild, non ethal heat stress can prolong lifespan. Although causal data are lacking in more complex animals, human observational research has linked sauna bathing to cardiovascular protection and improved age related outcomes. To examine whether sauna use may influence aging related biology, we retrospectively analyzed longitudinal whole-blood methylomic data from 18 firefighters who used a portable sauna. A separately processed cohort of 36 matched adults provided descriptive context; firefighters showed higher DNA methylation estimated maximal oxygen uptake (DNAmVO2 max), lower AdaptAge, and higher DamAge. After 8 to 18 weeks, eight predictors met a within family Benjamini Hochberg false discovery rate (FDR) threshold of <0.05 underage/sex-adjusted epigenetic age acceleration: PCDNAmTL, DepressionBarbu, SystemsAge Blood, SystemsAge Lung, DNAmPulsePressure, DNAmHDL, DNAmCystatinC, and DNAmDHEAS. DNAmDHEAS increased, whereas the other predictors changed in directions consistent with short term findings for high intensity interval training, another hormetic stressor. None met the within family FDR threshold after adjustment for 12 cell leukocyte composition, although effect estimates were not uniformly eliminated. At individual cytosine-phosphate-guanine (CpG) sites, BACON empirical null calibration retained 126 acute and 329 long-term candidates at P<0.0001; none was FDR-significant. DMRcate identified five acute and 140 long-term differentially methylated regions using a harmonic mean of individual CpG FDR values <0.05. Long-term gometh analysis also identified ATP binding cassette (ABC) transporter enrichment (FDR=0.026). These exploratory findings suggest that portable-sauna use may influence the blood methylome within 8 to 18 weeks while underscoring the importance of leukocyte-composition and technical sensitivity analyses.