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	Epigenetic Clock (DNA Methylation Age)	Healthy Aging Index Construction
Field	Social Gerontology	Social Gerontology
Family	Regression model	Process / pipeline
Year of origin	2013	2014
Originator	Steve Horvath	Jason L. Sanders, Anne B. Newman, and colleagues (Cardiovascular Health Study; Long Life Family Study)
Type	Penalized-regression predictor of age from DNA methylation	Composite physiologic index of multisystem biological aging
Seminal source	Horvath, S. (2013). DNA methylation age of human tissues and cell types. Genome Biology, 14(10), R115.	Sanders, J. L., Minster, R. L., Barmada, M. M., Matteini, A. M., Boudreau, R. M., Christensen, K., Walston, J. D., Newman, A. B. (2014). Heritability of and mortality prediction with a longevity phenotype: the healthy aging index. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 69(4), 479-485.
Aliases	DNAm Age, Horvath Clock, DNA Methylation Clock, Methylation Age Predictor	HAI, Healthy Ageing Index, Multisystem Healthy Aging Index, Physiologic Aging Index
Related	4	4
Summary	An epigenetic clock is a statistical predictor that estimates age from patterns of DNA methylation, the chemical marks on the genome that change in a regular way over the life course. The most influential is Steve Horvath's 2013 multi-tissue clock, which predicts chronological age from methylation levels at 353 specific CpG sites using a penalized regression model. Methylation is measured as a beta-value between zero and one at each site, representing the fraction of cells in which that site is methylated, and the clock combines a weighted set of these values into a predicted DNA methylation age, or DNAm age. Remarkably, Horvath's clock works across many tissues and cell types from the same individual, suggesting it captures a fundamental aging process rather than a tissue-specific quirk. The difference between predicted DNAm age and actual chronological age, known as epigenetic age acceleration, serves as a biomarker of biological aging. Age acceleration predicts mortality and a range of age-related conditions, which has made epigenetic clocks central to modern aging research.	The Healthy Aging Index (HAI) is a simple composite that summarizes the burden of subclinical physiologic decline across several organ systems into a single score. Introduced by Jason Sanders, Anne Newman, and colleagues in 2014 using the Cardiovascular Health Study, it captures the idea that biological aging is a multisystem process rather than the failure of any one organ. The index combines five readily measured markers, one from each of five physiologic systems: systolic blood pressure (vascular), fasting glucose (metabolic), Mini-Mental State Examination score (cognitive), serum creatinine (renal), and forced vital capacity (pulmonary). Each marker is scored 0, 1, or 2 according to which tertile of risk an individual falls into, and the five scores are summed to give a total from 0 to 10, with higher values indicating worse aging. The HAI predicts mortality and was shown to be heritable, supporting its interpretation as a phenotype of biological aging. Its appeal lies in being inexpensive, transparent, and built from routine clinical measurements rather than specialized assays.