Early-life smoking, cardiovascular disease risk, and the mediating role of DNA methylation biomarkers of aging

BACKGROUND: Early-life smoking is linked to biological aging and chronic diseases, yet its specific relationship with cardiovascular disease (CVD) risk and the role of DNA methylation biomarkers of aging as potential mediators of that relationship remain underexplored. METHODS: In this study, we analyzed data from 2345 participants in the National Health and Nutrition Examination Survey (NHANES; 1999-2002). Early-life smoking status was assessed on the basis of the age of smoking initiation (ASI) and categorized into three smoking initiation periods (SIPs): childhood (5-14 years), adolescence/adulthood (> 14 years), and never smoked. DNA methylation biomarkers of aging (DNAm PhenoAge, DunedinPoAm, HorvathTelo) were measured, and CVD outcomes were determined via self-reported, physician-confirmed diagnoses. Multivariate logistic regression and causal mediation analyses were performed to assess the associations between SIP and CVD outcomes and explore the mediating effects of DNA methylation biomarkers on those associations. RESULTS: Earlier smoking initiation was more strongly associated with an increased risk of developing CVD, with childhood smoking showing the highest risk (OR = 1.95, 95% CI: 1.15-3.29; P = 0.013). Furthermore, DNA methylation biomarkers of aging were independently associated with increased CVD risk (1-year increase in DNAm PhenoAge: OR = 1.03, 95% CI: 1.01-1.05, P < 0.001; 0.1-unit increase in DunedinPoAm: OR = 1.19, 95% CI: 1.00-1.40, P < 0.05; 1-kb increase in HorvathTelo: OR = 0.57, 95% CI: 0.34-0.96, P < 0.05). Subgroup analysis revealed that the association between early-life smoking status and the risk of developing CVD was stronger among individuals without household smoking exposure (P for interaction = 0.035). Moreover, compared with early-life smoking status, later smoking initiation status was correlated with delayed epigenetic aging, as indicated by lower DNAm PhenoAge (β=-0.02, 95% CI: -0.03--0.01, P < 0.01), slower DunedinPoAm (β=-0.01, 95% CI: -0.01--0.01, P < 0.001), and longer HorvathTelo (β = 0.01, 95% CI: 0.01-0.01, P < 0.001). Mediation analysis revealed that DNAm PhenoAge significantly mediated the relationship between early-life smoking status and CVD risk, accounting for 6% of the total effect (ASI: ACME=-0.000100, P = 0.010; SIP: ACME = 0.004796, P = 0.022). CONCLUSION: Early-life smoking status is associated with significantly increased CVD risk. DNAm PhenoAge partially mediates this relationship, suggesting its potential as a target for prevention. Moreover, these findings highlight the need for early smoking prevention to reduce CVD risk.