Space-Earth connection: How space weather fluctuations impact epigenetic aging in an elderly men cohort from Massachusetts, USA.

Background: In a previous study, we reported associations between space weather [galactic cosmic rays (GCRs)] and solar and geomagnetic activities (SGAs)] with shorter telomere length in a cohort of elderly men in Massachusetts. Here, we investigated the impact of space weather on epigenetic aging in the same cohort. Methods: We analyzed 1,487 blood DNA methylation measures from 771 older men in the Normative Aging Study (1999-2013). Daily space weather indicators were obtained from NASA including sunspot number (SSN) and interplanetary magnetic field as solar activity parameters, Kp-index as a geomagnetic parameter, and neutron monitors and modeled cosmic ray-induced ionization as measures of GCRs. The 30-day moving average of each parameter was prespecified as the exposure window. Four epigenetic age acceleration metrics, including HorvathAgeAccel, HannumAgeAccel, PhenoAgeAccel, and GrimAgeAccel, were derived, and exploratory epigenome-wide association study (EWAS) and pathway enrichment analyses were conducted. Results: GCRs were associated with accelerated epigenetic aging, whereas SGAs were associated with slower aging. Each interquartile range increase in SSN corresponded to a 0.61-year lower HorvathAgeAccel and 0.50-year lower PhenoAgeAccel, while higher neutron counts were associated with 0.32-year greater HorvathAgeAccel and 0.29-year greater HannumAgeAccel. EWAS identified hundreds of CpGs associated with GCRs (predominantly lower methylation) and thousands with SGAs (predominantly higher methylation), enriched in genome maintenance pathways such as P53 signaling, DNA repair, and inflammatory response, consistent with astronaut studies showing activation of similar stress and repair pathways. Conclusion: Short-term space weather fluctuations were associated with distinct epigenetic aging patterns in blood, suggesting that, as observed in astronauts, terrestrial populations may likewise show biological sensitivity to space weather variability.