The Effect of Tobacco Smoking Differs across Indices of DNA Methylation-Based Aging in an African American Sample: DNA Methylation-Based Indices of Smoking Capture These Effects

Epigenetic Aging Helps Explain Differential Resilience in Older Adults

Past research suggests that resilience to health hazards increases with age, potentially because less resilient individuals die at earlier ages, leaving behind their more resilient peers. Using lifetime cigarette smoking as a model health hazard, we examined whether accelerated epigenetic aging (indicating differences in the speed of individuals' underlying aging process) helps explain age-related resilience in a nationally representative sample of 3,783 older U.S. adults from the Health and Retirement Study. Results of mediation moderation analyses indicated that participants aged 86 or older showed a weaker association between lifetime cigarette smoking and mortality relative to participants aged 76-85 and a weaker association between smoking and multimorbidity relative to all younger cohorts. This moderation effect was mediated by a reduced association between smoking pack-years and epigenetic aging. This research helps identify subpopulations of particularly resilient individuals and identifies epigenetic aging as a potential mechanism explaining this process. Interventions in younger adults could utilize epigenetic aging estimates to identify the most vulnerable individuals and intervene before adverse health outcomes, such as chronic disease morbidity or mortality, manifest.

Accelerated epigenetic age, inflammation, and gene expression in lung: comparisons of smokers and vapers with non-smokers

BACKGROUND

Cigarette smoking and aging are the main risk factors for pulmonary diseases, including cancer. Epigenetic aging may explain the relationship between smoking, electronic cigarette vaping, and pulmonary health. No study has examined smoking and vaping-related epigenetic aging in relation to lung biomarkers.

METHODS

Lung epigenetic aging measured by DNA methylation (mAge) and its acceleration (mAA) was assessed in young (age 21-30) electronic cigarette vapers (EC, n = 14, including 3 never-smoking EC), smokers (SM, n = 16), and non-EC/non-SM (NS, n = 39). We investigated relationships of mAge estimates with chronological age (Horvath-mAge), lifespan/mortality (Grim-mAge), telomere length (TL-mAge), smoking/EC history, urinary biomarkers, lung cytokines, and transcriptome.

RESULTS

Compared to NS, EC and SM had significantly older Grim-mAge, shorter TL-mAge, significantly accelerated Grim-mAge and decelerated TL-mAge. Among SM, Grim-mAA was associated with nicotine intake and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL). For EC, Horvath-mAA was significantly correlated with puffs per day. Overall, cytokines (IL-1β, IL-6, and IL-8) and 759 transcripts (651 unique genes) were significantly associated with Grim-mAA. Grim-mAA-associated genes were highly enriched in immune-related pathways and genes that play a role in the morphology and structures of cells/tissues.

CONCLUSIONS

Faster lung mAge for SM is consistent with prior studies of blood. Faster lung mAge for EC compared to NS indicates possible adverse pulmonary effects of EC on biological aging. Our findings support further research, particularly on epigenetic markers, on effects of smoking and vaping on pulmonary health. Given that most EC are former smokers, further study is needed to understand unique effects of electronic cigarettes on biological aging.

Intrinsic and environmental basis of aging: A narrative review

Longevity has been a topic of interest since the beginnings of humanity, yet its aetiology and precise mechanisms remain to be elucidated. Aging is currently viewed as a physiological phenomenon characterized by the gradual degeneration of organic physiology and morphology due to the passage of time where both external and internal stimuli intervene. The influence of intrinsic factors, such as progressive telomere shortening, genome instability due to mutation buildup, the direct or indirect actions of age-related genes, and marked changes in epigenetic, metabolic, and mitochondrial patterns constitute a big part of its underlying endogenous mechanisms. On the other hand, several psychosocial and demographic factors, such as diet, physical activity, smoking, and drinking habits, may have an even more significant impact on shaping the aging process. Consequentially, implementing dietary and exercise patterns has been proposed as the most viable alternative strategy for attenuating the most typical degenerative aging changes, thus increasing the likelihood of prolonging lifespan and achieving successful aging.

Targeted DNA methylation analysis and prediction of smoking habits in blood based on massively parallel sequencing

Tobacco smoking is a frequent habit sustained by > 1.3 billion people in 2020 and the leading preventable factor for health risk and premature mortality worldwide. In the forensic context, predicting smoking habits from biological samples may allow broadening DNA phenotyping. In this study, we aimed to implement previously published smoking habit classification models based on blood DNA methylation at 13 CpGs. First, we developed a matching lab tool based on bisulfite conversion and multiplex PCR followed by amplification-free library preparation and targeted paired-end massively parallel sequencing (MPS). Analysis of six technical duplicates revealed high reproducibility of methylation measurements (Pearson correlation of 0.983). Artificially methylated standards uncovered marker-specific amplification bias, which we corrected via bi-exponential models. We then applied our MPS tool to 232 blood samples from Europeans of a wide age range, of which 90 were current, 71 former and 71 never smokers. On average, we obtained 189,000 reads/sample and 15,000 reads/CpG, without marker drop-out. Methylation distributions per smoking category roughly corresponded to previous microarray analysis, showcasing large inter-individual variation but with technology-driven bias. Methylation at 11 out of 13 smoking-CpGs correlated with daily cigarettes in current smokers, while solely one was weakly correlated with time since cessation in former smokers. Interestingly, eight smoking-CpGs correlated with age, and one displayed weak but significant sex-associated methylation differences. Using bias-uncorrected MPS data, smoking habits were relatively accurately predicted using both two- (current/non-current) and three- (never/former/current) category model, but bias correction resulted in worse prediction performance for both models. Finally, to account for technology-driven variation, we built new, joint models with inter-technology corrections, which resulted in improved prediction results for both models, with or without PCR bias correction (e.g. MPS cross-validation F₁-score > 0.8; 2-categories). Overall, our novel assay takes us one step closer towards the forensic application of viable smoking habit prediction from blood traces. However, future research is needed towards forensically validating the assay, especially in terms of sensitivity. We also need to further shed light on the employed biomarkers, particularly on the mechanistics, tissue specificity and putative confounders of smoking epigenetic signatures.

Do Loneliness and Per Capita Income Combine to Increase the Pace of Biological Aging for Black Adults across Late Middle Age?

In a sample of 685 late middle-aged Black adults (M age at 2019 = 57.17 years), we examined the effects of loneliness and per capita income on accelerated aging using a newly developed DNA-methylation based index: the DunedinPACE. First, using linear, mixed effects regression in a growth curve framework, we found that change in DunedinPACE was dependent on age, with a linear model best fitting the data (b = 0.004, p < 0.001), indicating that average pace of change increased among older participants. A quadratic effect was also tested, but was non-significant. Beyond the effect of age, both change in loneliness (b = 0.009, p < 0.05) and change in per capita income (b = -0.016, p < 0.001) were significantly associated with change in DunedinPACE across an 11-year period, accounting for significant between person variability observed in the unconditional model. Including non-self-report indices of smoking and alcohol use did not reduce the association of loneliness or per capita income with DunedinPACE. However, change in smoking was strongly associated with change in DunedinPACE such that those reducing their smoking aged less rapidly than those continuing to smoke. In addition, both loneliness and per capita income were associated with DunedinPACE after controlling for variation in cell-types.

Relative contributions of six lifestyle- and health-related exposures to epigenetic aging: the Coronary Artery Risk Development in Young Adults (CARDIA) Study

Background

DNA methylation-based GrimAge acceleration (GrimAA) is associated with a wide range of age-related health outcomes including cardiovascular disease. Since DNA methylation is modifiable by external and behavioral exposures, it is important to identify which of these exposures may have the strongest contributions to differences in GrimAA, to help guide potential intervention strategies. Here, we assessed the relative contributions of lifestyle- and health-related components, as well as their collective association, to GrimAA.

Results

We included 744 participants (391 men and 353 women) from the Coronary Artery Risk Development in Young Adults (CARDIA) study with blood DNA methylation information at CARDIA Exam Year (Y) 20 (2005–2006, mean age 45.9 years). Six cumulative exposures by Y20 were included in the analysis: total packs of cigarettes, total alcohol consumption, education years, healthy diet score, sleep hours, and physical activity. We used quantile-based g-computation (QGC) and Bayesian kernel machine regression (BKMR) methods to assess the relative contribution of each exposure to a single overall association with GrimAA. We also assessed the collective association of the six components combined with GrimAA. Smoking showed the greatest positive contribution to GrimAA, accounting for 83.5% of overall positive associations of the six exposures with GrimAA (QGC weight = 0.835). The posterior inclusion probability (PIP) of smoking also achieved the highest score of 1.0 from BKMR analysis. Healthy diet and education years showed inverse contributions to GrimAA. We observed a U-shaped pattern in the contribution of alcohol consumption to GrimAA. While smoking was the greatest contributor across sex and race subgroups, the relative contributions of other components varied by subgroups.

Conclusions

Smoking, alcohol consumption, and education showed the highest contributions to GrimAA in our study. Higher amounts of smoking and alcohol consumption were likely to contribute to greater GrimAA, whereas achieved education was likely to contribute to lower GrimAA. Identifying pertinent lifestyle- and health-related exposures in a context of collective components can provide direction for intervention strategies and suggests which components should be the primary focus for promoting younger GrimAA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13148-022-01304-9.

Intervention effects on self-control decrease speed of biological aging mediated by changes in substance use: A longitudinal study of African American youth

Biological aging is a common root for multiple diseases causing morbidity and mortality, and trajectories of aging may start early in life. This study was designed to examine whether a universal family-based substance use preventive intervention to enhance self-control and reduce substance use would also result in reductions in biological aging among Black youth from the rural South. The Adults in the Making (AIM) program is a randomized controlled trial with six 2-h sessions for Black youth. The 216 youths agreeing to provide blood at age 22 included 114 who had received the AIM intervention and 102 who assigned to the control group. We examined accelerated DNA methylation (DNAm)-based aging using a recently developed measure, "GrimAge," that has been shown to predict the risk of early mortality and that is known to be more strongly affected by substance use than other DNAm-based aging indices. Relative to those randomly assigned to the control group, those receiving the intervention demonstrated significantly enhanced self-control, slower increases in substance use, and reduced Grim aging at age 22. Using a bootstrapping method with 1000 replications, we found a significant indirect effect of AIM on reduced Grim aging through its effect on self-control and substance use. Sensitivity analyses examined effects using other indices of DNAm-based aging. These findings suggest that a family-based program designed to enhance rural Black youth's self-control can have beneficial effects on self-control, enhancing young adult health and health behavior, and ultimately decreased mortality risk.

Lifetime exposure to smoking, epigenetic aging, and morbidity and mortality in older adults

BACKGROUND

Cigarette smoke is a major public health concern. Epigenetic aging may be an important pathway by which exposure to cigarette smoke affects health. However, little is known about how exposure to smoke at different life stages affects epigenetic aging, especially in older adults. This study examines how three epigenetic aging measures (GrimAge, PhenoAge, and DunedinPoAm38) are associated with parental smoking, smoking in youth, and smoking in adulthood, and whether these epigenetic aging measures mediate the link between smoke exposure and morbidity and mortality. This study utilizes data from the Health and Retirement Study (HRS) Venous Blood Study (VBS), a nationally representative sample of US adults over 50 years old collected in 2016. 2978 participants with data on exposure to smoking, morbidity, and mortality were included.

RESULTS

GrimAge is significantly increased by having two smoking parents, smoking in youth, and cigarette pack years in adulthood. PhenoAge and DunedinPoAm38 are associated with pack years. All three mediate some of the effect of pack years on cancer, high blood pressure, heart disease, and mortality and GrimAge and DunedinPoAm38 mediate this association on lung disease.

CONCLUSIONS

Results suggest epigenetic aging is one biological mechanism linking lifetime exposure to smoking with development of disease and earlier death in later life. Interventions aimed at reducing smoking in adulthood may be effective at weakening this association.

Childhood adversity predicts black young adults' DNA methylation-based accelerated aging: A dual pathway model

We expand upon prior work (Gibbons et al., ) relating childhood stressor effects, particularly harsh childhood environments, to risky behavior and ultimately physical health by adding longer-term outcomes - deoxyribonucleic acid (DNA) methylation-based measures of accelerated aging (DNAm-aging). Further, following work on the effects of early exposure to danger (McLaughlin et al., ), we also identify an additional pathway from harsh childhood environments to DNAm-aging that we label the danger/FKBP5 pathway, which includes early exposure to dangerous community conditions that are thought to impact glucocorticoid regulation and pro-inflammatory mechanisms. Because different DNAm-aging indices provide different windows on accelerated aging, we contrast effects on early indices of DNAm-aging based on chronological age with later indices that focused on predicting biological outcomes. We utilize data from Family and Community Health Study participants (N = 449) from age 10 to 29. We find that harshness influences parenting, which, in turn, influences accelerated DNAm-aging through the risky cognitions and substance use (i.e., behavioral) pathway outlined by Gibbons et al. (). Harshness is also associated with increased exposure to threat/danger, which, in turn, leads to accelerated DNAm-aging through effects on FKBP5 activity and enhanced pro-inflammatory tendencies (i.e., the danger/FKBP5 pathway).

Cancer-related accelerated ageing and biobehavioural modifiers: a framework for research and clinical care

A growing body of evidence indicates that patients with cancer who receive cytotoxic treatments (such as chemotherapy or radiotherapy) have an increased risk of accelerated physical and cognitive ageing. Furthermore, accelerated biological ageing is a suspected driving force behind many of these observed effects. In this Review, we describe the mechanisms of biological ageing and how they apply to patients with cancer. We highlight the important role of specific behavioural factors, namely stress, sleep and lifestyle-related factors such as physical activity, weight management, diet and substance use, in the accelerated ageing of patients with cancer and cancer survivors. We also present a framework of how modifiable behaviours could operate to either increase the risk of accelerated ageing, provide protection, or promote resilience at both the biological level and in terms of patient-reported outcomes.

Neighborhood structural disadvantage and biological aging in a sample of Black middle age and young adults

OBJECTIVES

Research on the social determinants of health has suggested that neighborhood disadvantage may undermine healthy aging and is particularly relevant for understanding health disparities. Recently, this work has examined deoxyribonucleic acid methylation (DNAm)-based measures of biological aging to understand the risk factors for morbidity and mortality. However, it is unknown whether neighborhood disadvantage is related to different indices of DNAm-based aging among Black Americans and whether such neighborhood effects vary as a function of age or gender.

METHODS

Our analyses of a Black American sample included 448 young adults and 493 middle-aged adults. We measured neighborhood disadvantage using the Area Deprivation Index at the census block group level. DNAm-based accelerated aging indices were measured using established procedures. Regressions with clustered standard errors were used for the analysis.

RESULTS

Neighborhood disadvantage was independently associated with acceleration in PhenoAge, GrimAge, and DunedinPoAm, among young and middle-aged adults. Further, there was no evidence that gender conditioned the effects of neighborhood disadvantage on the aging indices.

CONCLUSIONS

Regardless of age groups or gender, accelerated biological aging among Black Americans is partly rooted in differences in neighborhood disadvantage. From a policy standpoint, our findings suggest that programs that decrease neighborhood disadvantage are likely to increase healthy aging, especially among Black Americans.

Effect of Physical Activity, Smoking, and Sleep on Telomere Length: A Systematic Review of Observational and Intervention Studies

Aging is a risk factor for several pathologies, restricting one’s health span, and promoting chronic diseases (e.g., cardiovascular and neurodegenerative diseases), as well as cancer. Telomeres are regions of repetitive DNA located at chromosomal ends. Telomere length has been inversely associated with chronological age and has been considered, for a long time, a good biomarker of aging. Several lifestyle factors have been linked with telomere shortening or maintenance. However, the consistency of results is hampered by some methodological issues, including study design, sample size, measurement approaches, and population characteristics, among others. Therefore, we aimed to systematically review the current literature on the effects of three relevant lifestyle factors on telomere length in human adults: physical activity, smoking, and sleep. We conducted a qualitative systematic review of observational and intervention studies using the Preferred Reporting Item for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The systematic literature search covered articles published in MEDLINE and EMBASE databases (from 2010 to 2020). A total of 1400 studies were identified; 83 were included after quality control. Although fewer sedentary activities, optimal sleep habits, and non- or ex-smoker status have been associated with less telomere shortening, several methodological issues were detected, including the need for more targeted interventions and standardized protocols to better understand how physical activity and sleep can impact telomere length and aging. We discuss the main findings and current limitations to gain more insights into the influence of these lifestyle factors on the healthy aging process.

When Anger Remains Unspoken: Anger and Accelerated Epigenetic Aging Among Stress-Exposed Black Americans

OBJECTIVE

Race-related lifetime stress exposure (LSE) including racial discrimination, trauma, and stressful life events have been shown to contribute to racial health disparities. However, little is known about associations between race-related stressors and premature biological aging that confer the risk of adverse health outcomes. Even less is known about the mechanisms through which race-related stressors may be associated with accelerated aging. Early evidence suggests psychological processes such as anger, and particularly the internalization of anger, may play a role.

METHODS

In a community sample of predominantly low-income Black adults (n = 219; age = 45.91 [12.33] years; 64% female), the present study examined the association of race-related LSE (as defined by exposure to racial discrimination, trauma, and stressful life events) and epigenetic age acceleration through anger expression.

RESULTS

Internalized and externalized anger expression were each significantly associated with LSE and age acceleration. Although LSE was not directly associated with age acceleration (ΔR2 = 0.001, p = .64), we found that greater LSE was indirectly associated with age acceleration through increases in internalized, but not externalized, anger (indirect effect: β = 0.03, standard error = 0.02, 95% confidence interval = 0.003 to 0.08; total effect: β = 0.02, 95% confidence interval = -0.25 to 0.31).

CONCLUSIONS

These results suggest race-related LSE may elicit the internalization of anger, which, along with the externalization of anger, may initiate detrimental epigenetic alterations that confer the risk of adverse health outcomes. These findings lay the groundwork for longitudinal studies of the association between race-related stress and racial health disparities.

Methylation of FKBP5 is associated with accelerated DNA methylation ageing and cardiometabolic risk: replication in young-adult and middle-aged Black Americans

Methylation of FKBP5 is involved in the regulation of the stress response and is influenced by early stress exposure. Two CpG sites, cg20813374 and cg00130530, have been identified as potential reporters of early stress. We examined whether FKBP5 methylation was associated with accelerated DNA methylation ageing and indirectly predicted poorer cardiovascular health among both young adult and middle-aged Black Americans. Four hundred and forty-nine young adults, with a mean age of 28.67 and N = 469 middle-age parents and their current partners with a mean age of 57.21, provided self-reports, biometric assessments, and blood draws. Methylation values were obtained using the Illumina Epic Array. Cardiometabolic risk was calculated by summing the standardized log-transformed scores for the body mass index, mean arterial blood pressure, and HbA1c. We also used a more standard index of risk, the Framingham 10-year cardiometabolic risk index, as an alternative measure of cardiometabolic risk. To measure accelerated ageing, four widely used indices of accelerated, DNA methylation-based ageing were used controlling sex, age, other variation in FKBP5, and cell-type. Exposure to community danger was associated with demethylation of FKBP5. FKBP5 methylation was significantly associated with accelerated ageing for both young-adult and middle-aged samples, with significant indirect effects from FKBP5 methylation to cardiometabolic risk through accelerated ageing for both. Early exposure to danger may influence FKBP5 methylation. In turn, FKBP5 methylation may help explain intrinsic accelerated ageing and elevated cardiometabolic risk in adulthood for Black Americans.

Hypomethylation of AHRR (cg05575921) Is Related to Smoking Status in the Mexican Mestizo Population

Tobacco smoking results in a multifactorial disease involving environmental and genetic factors; epigenome-wide association studies (EWAS) show changes in DNA methylation levels due to cigarette consumption, partially reversible upon tobacco smoking cessation. Therefore, methylation levels could predict smoking status. This study aimed to evaluate the DNA methylation level of cg05575921 (AHRR) and cg23771366 (PRSS23) and their correlation with lung function variables, cigarette consumption, and nicotine addiction in the Mexican smoking population. We included 114 non-smokers (NS) and 102 current tobacco smokers (TS); we then further subclassified them as heavy smokers (HS) (n = 53) and light smokers (LS) (n = 49). We used restriction enzymes (MspI/HpaII) and qPCR to determine the DNA methylation level. We observed significant hypomethylation of cg05575921 in smokers compared to NS (p = 0.003); further analysis found a difference between HS and NS (p = 0.02). We did not observe differences between other groups or a positive correlation between methylation levels and age, BMI, cigarette consumption, nicotine addiction, or lung function. In conclusion, the cg05575921 site of AHRR is significantly hypomethylated in Mexican smokers, especially in HS (≥20 cigarettes per day).

Life course socioeconomic position and DNA methylation age acceleration in mid-life

Background

Ageing biomarkers can help us better understand how well-established socioeconomic position (SEP) disparities in ageing occur. A promising new set of DNAm methylation (DNAm)-based ageing biomarkers indicate through their age acceleration (AA) measures if biological ageing is slower or faster than chronological ageing. Few studies have investigated the association between SEP and DNAm AA.

Methods

We used linear regression to examine the sex-adjusted relationships between childhood social class, adult social class, intergenerational social class change, education and adult household earnings with first (Horvath AA and Hannum AA) and second generation (PhenoAge AA and GrimAge AA) DNAm AA markers using data from the MRC National Survey of Health and Development.

Results

In the first-generation biomarkers, there was little evidence of any associations with Horvath AA but associations of childhood social class and income with Hannum AA were observed. Strong associations were seen between greater disadvantage in childhood and adult SEP and greater AA in the second generation biomarkers. For example, those with fathers in an unskilled occupational social class in childhood had 3.6 years greater PhenoAge AA (95% CI 1.8 to 5.4) than those with fathers from a professional social class. Individuals without qualifications had higher AA compared with those with higher education (4.1 years greater GrimAge AA (95% CI 3.1 to 5.0)).

Conclusion

Our findings highlight the importance of exposure to social disadvantage in childhood to the biological ageing process. The second generation clocks appear to be more sensitive to the accumulation of social disadvantage across the life course.

Leisure-Time and Occupational Physical Activity Associates Differently with Epigenetic Aging

PURPOSE

Greater leisure-time physical activity (LTPA) associates with healthier lives, but knowledge regarding occupational physical activity (OPA) is more inconsistent. DNA methylation (DNAm) patterns capture age-related changes in different tissues. We aimed to assess how LTPA and OPA are associated with three DNAm-based epigenetic age estimates, namely, DNAm age, PhenoAge, and GrimAge.

METHODS

The participants were young adult (21-25 yr, n = 285) and older (55-74 yr, n = 235) twin pairs, including 16 pairs with documented long-term LTPA discordance. Genome-wide DNAm from blood samples was used to compute DNAm age, PhenoAge, and GrimAge Age acceleration (Acc), which describes the difference between chronological and epigenetic ages. Physical activity was assessed with sport, leisure-time, and work indices based on the Baecke Questionnaire. Genetic and environmental variance components of epigenetic age Acc were estimated by quantitative genetic modeling.

RESULTS

Epigenetic age Acc was highly heritable in young adult and older twin pairs (~60%). Sport index was associated with slower and OPA with faster DNAm GrimAge Acc after adjusting the model for sex. Genetic factors and nonshared environmental factors in common with sport index explained 1.5%-2.7% and 1.9%-3.5%, respectively, of the variation in GrimAge Acc. The corresponding proportions considering OPA were 0.4%-1.8% and 0.7%-1.8%, respectively. However, these proportions were minor (<0.5%) after adjusting the model for smoking status.

CONCLUSIONS

LTPA associates with slower and OPA with faster epigenetic aging. However, adjusting the models for smoking status, which may reflect the accumulation of unhealthy lifestyle habits, attenuated the associations.

Epigenome-450K-wide methylation signatures of active cigarette smoking: The Young Finns Study

Smoking as a major risk factor for morbidity affects numerous regulatory systems of the human body including DNA methylation. Most of the previous studies with genome-wide methylation data are based on conventional association analysis and earliest threshold-based gene set analysis that lacks sensitivity to be able to reveal all the relevant effects of smoking. The aim of the present study was to investigate the impact of active smoking on DNA methylation at three biological levels: 5'-C-phosphate-G-3' (CpG) sites, genes and functionally related genes (gene sets). Gene set analysis was done with mGSZ, a modern threshold-free method previously developed by us that utilizes all the genes in the experiment and their differential methylation scores. Application of such method in DNA methylation study is novel. Epigenome-wide methylation levels were profiled from Young Finns Study (YFS) participants' whole blood from 2011 follow-up using Illumina Infinium HumanMethylation450 BeadChips. We identified three novel smoking related CpG sites and replicated 57 of the previously identified ones. We found that smoking is associated with hypomethylation in shore (genomic regions 0-2 kilobases from CpG island). We identified smoking related methylation changes in 13 gene sets with false discovery rate (FDR) ≤ 0.05, among which is olfactory receptor activity, the flagship novel finding of the present study. Overall, we extended the current knowledge by identifying: (i) three novel smoking related CpG sites, (ii) similar effects as aging on average methylation in shore, and (iii) a novel finding that olfactory receptor activity pathway responds to tobacco smoke and toxin exposure through epigenetic mechanisms.

Array-Based Epigenetic Aging Indices May Be Racially Biased

Epigenetic aging (EA) indices are frequently used as predictors of mortality and other important health outcomes. However, each of the commonly used array-based indices has significant heritable components which could tag ethnicity and potentially confound comparisons across racial and ethnic groups. To determine if this was possible, we examined the relationship of DNA methylation in cord blood from 203 newborns (112 African American (AA) and 91 White) at the 513 probes from the Levine PhenoAge Epigenetic Aging index to ethnicity. Then, we examined all sites significantly associated with race in the newborn sample to determine if they were also associated with an index of ethnic genetic heritage in a cohort of 505 AA adults. After Bonferroni correction, methylation at 50 CpG sites was significantly associated with ethnicity in the newborn cohort. The five most significant sites predicted ancestry with a receiver operator characteristic area under the curve of 0.97. Examination of the top 50 sites in the AA adult cohort showed that methylation status at 11 of those sites was also associated with percentage European ancestry. We conclude that the Levine PhenoAge Index is influenced by cryptic ethnic-specific genetic influences. This influence may extend to similarly constructed EA indices and bias cross-race comparisons.