Association of Smoking Behavior, Intensity, and Time Since Cessation with Epigenetic Aging Biomarkers: Results from NHANES 1999-2002.

Background: Smoking is a major preventable risk factor for all-cause mortality and disability worldwide. It leads to age-related diseases, but the effects and reversibility of smoking behaviors on different epigenetic clocks are not fully explored. Objective: To characterize the association of epigenetic age acceleration in whole blood with active and secondhand smoking (SHS), smoking intensity, and time since cessation among U.S. adults. Methods: This is a cross-sectional study in adults from the NHANES 1999-2002 survey cycles, a population-based survey representative of the U.S. adult civilian noninstitutionalized population. We analyzed 2,320 adults aged ≥50 years, including non-Hispanic White, non-Hispanic Black, Mexican American, and other populations. Those without available self-reported smoking status data were excluded. Smoking exposure was analyzed in terms of self-reported smoking status (current, former, never), intensity (packs in the last month), years since smoking cessation, and SHS (serum cotinine levels: 0.05-10 ng/ml). Epigenetic age was estimated using 12 DNA methylation age biomarkers. Survey-weighted linear models were used to estimate the association of smoking exposure with epigenetic age acceleration while adjusting for confounders and multiple comparisons. Results: We analyzed 1,043 never, 903 former, and 374 current smokers (mean age: 65.1±9.3 years, female: 49.1%). GrimAge2 was 9.1 years (95% CI: 8.0, 10.2) and 2.8 years (95% CI: 2.3, 3.3) higher in current and former smokers, respectively, than in never smokers. Smokers showed an increased pace of aging, with current smokers aging 0.15 (95% CI: 0.13, 0.17) and former smokers 0.04 (95% CI: 0.03, 0.05) additional years per chronological year, and shorter methylation-predicted telomere length (current: -132±19 bp; former: -30±15 bp). Each cigarette pack smoked in the past month was associated with increases of 0.1 years in GrimAge2 and PhenoAge, and 0.01 aged months/year in aging pace. Among former smokers, each year since smoking cessation was associated with a deceleration of -0.14 (GrimAge2) and -0.06 (PhenoAge) years, and -0.03 aged months/year in aging pace. Cotinine analyses supported dose-dependent associations of epigenetic aging with smoking and suggested a 0.8-year increase in GrimAge2 with SHS exposure. Conclusions: Smoking was associated in a dose-dependent manner with accelerated epigenetic aging in former and current smokers. However, epigenetic age acceleration declines with time since smoking cessation among former smokers.