Epigenetic Biomarkers of Socioeconomic Status are Associated with Age-Related Chronic Diseases and Mortality in Older Adults

Later-life health is patterned by socioeconomic influences across the lifecourse. However, the pathways underlying the biological embedding of socioeconomic status (SES) and its consequences on downstream morbidity and mortality are not fully understood. Epigenetic markers like DNA methylation (DNAm) may be promising surrogates of underlying biological processes that can enhance our understanding of how SES shapes population health. Studies have shown that SES is associated with epigenetic aging measures, but few have examined relationships between early and later-life SES and DNAm sites across the epigenome. In this study, we trained and tested DNAm-based surrogates, or “biomarkers,” of childhood and adult SES in two large, multi-racial/ethnic samples of older adults—the Health and Retirement Study (HRS) (N=3,527) and the Multi-Ethnic Study of Atherosclerosis (MESA) (N=1,182). Both biomarkers were associated with downstream morbidity and mortality, and these associations persisted after controlling for measured SES, and in some cases, epigenetic aging clocks. Both childhood and adult SES biomarker CpG sites were enriched for genomic features that regulate gene expression (e.g., DNAse hypersensitivity sites and enhancers) and were implicated in prior epigenome-wide studies of inflammation, aging, and chronic disease. Distinct patterns also emerged between childhood CpGs and immune system dysregulation and adult CpGs and metabolic functioning, health behaviors, and cancer. Results suggest DNAm-based surrogate biomarkers of SES may be useful proxies for unmeasured social exposures that can augment our understanding of the biological mechanisms between social disadvantage and downstream health. Significance Statement Information on DNA methylation (DNAm)—an epigenetic modification that plays a central role in regulating gene expression—is increasingly available in large epidemiological studies. Since DNAm is relatively stable but responsive to environmental influences, genome-wide signatures are promising surrogates or biomarkers of exposure that may both shed light on biological mechanisms between adverse environments and downstream health and/or act as proxies for unmeasured exposures. To better understand the biological embedding of social disadvantage, this study trained and tested DNAm-based surrogates of childhood and adult socioeconomic status (SES) in two US-based cohorts of older adults. Findings reveal distinct DNAm signatures of SES that connect social adversity across the lifecourse with dysregulated immune system responses, inflammatory pathways, poorer metabolic functioning, chronic diseases, and cancer. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This analysis was supported by the National Institute on Aging (NIA, R00 AG056599 (Schmitz)), the National Heart, Lung, and Blood Institute (NHLBI, R01 HL141292 (Smith)), and the National Human Genome Research Institute (NHGRI, T32 HG000040 (Opsasnick)). The NIA supports the Health and Retirement Study (U01AG009740) and its genotyping (RC2 AG0336495, RC4 AG039029). Research in MESA is supported by contracts 75N92020D00001, HHSN268201500003I, N01-HC-95159, 75N92020D00005, N01-HC-95160, 75N92020D00002, N01-HC-95161, 75N92020D00003, N01-HC-95162, 75N92020D00006, N01-HC-95163, 75N92020D00004, N01-HC-95164, 75N92020D00007, N01-HC-95165, N01-HC-95166, N01-HC-95167, N01-HC-95168 and N01-HC-95169 from the NHLBI and by grants UL1-TR-000040, UL1-TR-001079, and UL1-TR-001420 from the National Center for Advancing Translational Sciences (NCATS). The provision of genotyping data was supported in part by the National Center for Advancing Translational Sciences, CTSI grant UL1TR001881, and the National Institute of Diabetes and Digestive and Kidney Disease Diabetes Research Center (DRC) grant DK063491 to the Southern California Diabetes Endocrinology Research Center. Funding for SHARe genotyping was provided by NHLBI Contract N02-HL-64278. A full list of participating MESA investigators and institutions can be found at http://www.mesa-nhlbi.org [mesa-nhlbi.org]. Funding for MESA SHARe genotyping was provided by NHLBI Contract N02-HL-64278. Genotyping was performed at Affymetrix (Santa Clara, California, USA) and the Broad Institute of Harvard and MIT (Boston, Massachusetts, USA) using the Affymetrix Genome-Wide Human SNP Array 6.0. The MESA Epigenomics & Transcriptomics Studies were funded by NIH grants R01HL101250, R01HL119962, R01DK101921, R01HL135009, and 1RF1AG054474. This paper has been reviewed and approved by the MESA Publications and Presentations Committee. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIA, NHLBI, NHGRI, or NCATS. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: IRBs of University of Wisconsin-Madison and University of Michigan gave ethical approval for this work. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes This study used restricted individual level information from the HRS, and our contractual agreement does not permit public dissemination of the data. Details on how to access restricted data for the HRS can be found at https://hrs.isr.umich.edu/data-products/restricted-data. Data used in this analysis from MESA can be obtained through the MESA Data Coordinating Center (https://www.mesanhlbi.org/) and through the database of Genotypes and Phenotypes (dbGaP; phs000209). Analysis code is posted on github: https://github.com/laurenschmitz/epigenetic-SES-biomarker.