Abstract
Repeated extreme environmental training (RET) enhances adaptability and induces lasting methylation modifications. We recruited 64 participants from a high-altitude region (4700 m), including 32 volunteers with repeated high-altitude exposure, reaching up to 8848 m and as many as 11 exposures. By analyzing 741,489 CpG loci and 39 phenotypes, we identified significant changes in 13 CpG loci (R(2) > 0.8, ACC > 0.75) and 15 phenotypes correlated with increasing RET exposures. The phenotypic Bayesian causal network and phenotypic-CpG interaction networks showed greater robustness (node correlation) with more RET exposures, particularly in systolic blood pressure (SP), platelet count (PLT), and neutrophil count (NEUT). Six CpG sites were validated as significantly associated with hypoxia exposure using the GEO public da-taset (AltitudeOmics). Furthermore, dividing the participants into two groups based on the number of RET exposures (n = 9 and 4) revealed six CpG sites significantly corre-lated with PLT and red cell distribution width-standard deviation (RDW.SD). Our findings suggest that increased RET exposures strengthen the interactions between phenotypes and CpG sites, indicating that critical extreme adaptive states may alter methylation patterns, co-evolving with phenotypes such as PLT, RDW.SD, and NEUT.