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categories: ["longevity"]categories: ["longevity"]tags: ["epigenetics", "biomarkers", "aging", "dna methylation", "measurement"]tags: ["epigenetics", "biomarkers", "aging", "dna methylation", "measurement"]summary: "Statistical predictors that estimate age or mortality risk from DNA methylation patterns at selected sites in the genome."summary: "Statistical predictors that estimate age or mortality risk from DNA methylation patterns at selected sites in the genome."updated: "2026-07-27"updated: "2026-10-28"humanEvidence: "Built and validated in large human cohorts, where age acceleration predicts mortality and disease modestly; no trial has shown that moving a clock reading changes an outcome."humanEvidence: "Built and validated in large human cohorts, where age acceleration predicts mortality and disease modestly; no trial has shown that moving a clock reading changes an outcome."access: "Sold direct to consumer as mail-in methylation tests and available as a research assay on standard arrays; no clock is an approved clinical test or an accepted regulatory endpoint."access: "Sold direct to consumer as mail-in methylation tests and available as a research assay on standard arrays; no clock is an approved clinical test or an accepted regulatory endpoint."reversibility: "reversible"reversibility: "reversible"lines 76–81 → 76–8361 unchanged lines not shown
Technical noise is a serious and underappreciated problem. Running the same DNA sample twice on the same array platform can produce clock estimates differing by more than a year, which is large relative to the effect sizes reported in intervention studies. Reconstructing clocks on principal components of the methylation data substantially improves test-retest reliability.[^higgins2022]Technical noise is a serious and underappreciated problem. Running the same DNA sample twice on the same array platform can produce clock estimates differing by more than a year, which is large relative to the effect sizes reported in intervention studies. Reconstructing clocks on principal components of the methylation data substantially improves test-retest reliability.[^higgins2022] Laboratory precision is not the same as stability in the body. A 2026 comparison of 18 clocks found that blood drawn from the same people a few hours or days apart agreed far less well than repeat assays of one sample: a meal, acute psychological stress or air pollution was enough to shift readings, no clock reached the conventional threshold for excellent reliability, and how reproducible a clock was in the laboratory did not predict how stable it was across repeat samples.[^sehgal2026] Cell composition is the other main confounder. Blood is a mixture, and the proportions of naive T cells, memory T cells, monocytes and granulocytes shift with age and with acute illness. A clock trained on whole blood partly measures that shift. Some clocks adjust for estimated cell counts; the adjustment is imperfect.Cell composition is the other main confounder. Blood is a mixture, and the proportions of naive T cells, memory T cells, monocytes and granulocytes shift with age and with acute illness. A clock trained on whole blood partly measures that shift. Some clocks adjust for estimated cell counts; the adjustment is imperfect. > [!caution] Contested> [!caution] Contestedlines 96–103 → 98–10714 unchanged lines not shown
## Consumer testing## Consumer testing Several companies sell direct-to-consumer methylation age tests, through the same mail-in channels asSeveral companies sell direct-to-consumer methylation age tests, through the same mail-in channels asthe [[consumer-blood-testing|direct-to-consumer laboratory panels]]. The assays are usually real, but the reported precision often exceeds what the underlying reliability supports, the clocks used are frequently proprietary and unpublished, and a result expressed as a single number invites over-interpretation of what is a noisy estimate with wide individual uncertainty. Repeat testing of the same person over short intervals can produce swings that reflect assay variation rather than any change in [[biological-age]]. Guidance from professional bodies has been consistently cautious about clinical use.the [[consumer-blood-testing|direct-to-consumer laboratory panels]]. The assays are usually real, but the reported precision often exceeds what the underlying reliability supports, the clocks used are frequently proprietary and unpublished, and a result expressed as a single number invites over-interpretation of what is a noisy estimate with wide individual uncertainty. Repeat testing of the same person over short intervals can produce swings that reflect assay variation or day-to-day biological fluctuation rather than any change in [[biological-age]]. As of October 2026 no consumer clock is an approved diagnostic test. The most publicised individual user is [[bryan-johnson]], who presents his DunedinPACE results as evidence for his [[blueprint-protocol|Blueprint]] regimen and runs a public leaderboard, the Rejuvenation Olympics, that ranks entrants by the same measure. In a 2025 post he reported a single reading of 0.48 and an average of 0.54 across three tests, described this as the world's slowest speed of aging, and said he chose the metric for "the robustness and reliability of the signal it measures".[^johnson2025] These are self-reported results for one person, with no control and a regimen that changes many things at once, and a lower reading is not by itself evidence that aging has slowed in function or in outcomes. DunedinPACE is highly reproducible when the same DNA is assayed twice, but the 2026 reliability study placed it among the less stable clocks across samples taken from the same person hours or days apart, and in the poor range across a laboratory stress test.[^sehgal2026] Daniel Belsky, who led its development and receives royalties from TruDiagnostic's consumer sales of the test, has said he would not restrict access to such tests "just because they're in beta testing", but that hearing of people basing health decisions on his tool makes him "a little anxious" and that he hopes users read results "with a grain of salt", since "any single result may have some error in it".[^zimmer2025] ## Outlook## Outlook Clocks are firmly established as research instruments and firmly unestablished as endpoints. The work that would change that is unglamorous: standardised assays, published reliability statistics, replication of intervention effects across independent cohorts, and demonstrations that a clock change predicts a later functional change in the same person. Competitions such as [[xprize-healthspan]] have deliberately chosen functional endpoints instead, on the view that measured muscle, cognitive and immune restoration is what the [[geroscience-hypothesis|geroscience]] argument ultimately has to deliver.Clocks are firmly established as research instruments and firmly unestablished as endpoints. The work that would change that is unglamorous: standardised assays, published reliability statistics, replication of intervention effects across independent cohorts, and demonstrations that a clock change predicts a later functional change in the same person. Competitions such as [[xprize-healthspan]] have deliberately chosen functional endpoints instead, on the view that measured muscle, cognitive and immune restoration is what the [[geroscience-hypothesis|geroscience]] argument ultimately has to deliver.lines 115–126 → 119–13311 unchanged lines not shown
## References## References [^horvath2013]: `paper` Horvath, S. "DNA methylation age of human tissues and cell types." *Genome Biology*, 2013. {Fitted to publicly available methylation datasets; the accuracy reported is against chronological age, the variable the model was trained on.}[^horvath2013]: `paper` Horvath, S. "DNA methylation age of human tissues and cell types." *Genome Biology*, 2013. {Fitted to publicly available methylation datasets; the accuracy reported is against chronological age, the variable the model was trained on.}[^hannum2013]: `paper` Hannum, G. et al. "Genome-wide methylation profiles reveal quantitative views of human aging rates." *Molecular Cell*, 2013.[^levine2018]: `paper` Levine, M.E. et al. "An epigenetic biomarker of aging for lifespan and healthspan." *Aging*, 2018.[^levine2018]: `paper` Levine, M.E. et al. "An epigenetic biomarker of aging for lifespan and healthspan." *Aging*, 2018.[^lu2019]: `paper` Lu, A.T. et al. "DNA methylation GrimAge strongly predicts lifespan and healthspan." *Aging*, 2019.[^lu2019]: `paper` Lu, A.T. et al. "DNA methylation GrimAge strongly predicts lifespan and healthspan." *Aging*, 2019.[^belsky2022]: `paper` Belsky, D.W. et al. "DunedinPACE, a DNA methylation biomarker of the pace of aging." *eLife*, 2022.[^belsky2022]: `paper` Belsky, D.W. et al. "DunedinPACE, a DNA methylation biomarker of the pace of aging." *eLife*, 2022.[^higgins2022]: `paper` Higgins-Chen, A.T. et al. "A computational solution for bolstering reliability of epigenetic clocks." *Nature Aging*, 2022.[^higgins2022]: `paper` Higgins-Chen, A.T. et al. "A computational solution for bolstering reliability of epigenetic clocks." *Nature Aging*, 2022.[^hannum2013]: `paper` Hannum, G. et al. "Genome-wide methylation profiles reveal quantitative views of human aging rates." *Molecular Cell*, 2013.[^sehgal2026]: `paper` Sehgal, R. et al. "Biological versus technical reliability of epigenetic clocks and implications for disease prognosis and intervention response." *Aging Cell*, 2026. {Two authors are named inventors of SystemsAge, among the clocks it rated most stable; the repeat samples spanned hours or days, not years.}[^fahy2019]: `paper` Fahy, G.M. et al. "Reversal of epigenetic aging and immunosenescent trends in humans." *Aging Cell*, 2019. {An uncontrolled study of nine men, run to test thymus regeneration rather than to test an intervention against a clock.}[^fahy2019]: `paper` Fahy, G.M. et al. "Reversal of epigenetic aging and immunosenescent trends in humans." *Aging Cell*, 2019. {An uncontrolled study of nine men, run to test thymus regeneration rather than to test an intervention against a clock.}[^waziry2023]: `paper` Waziry, R. et al. "Effect of long-term caloric restriction on DNA methylation measures of biological aging in healthy adults from the CALERIE trial." *Nature Aging*, 2023. {An analysis of stored samples from a trial designed to test caloric restriction, not to validate the clocks.}[^waziry2023]: `paper` Waziry, R. et al. "Effect of long-term caloric restriction on DNA methylation measures of biological aging in healthy adults from the CALERIE trial." *Nature Aging*, 2023. {An analysis of stored samples from a trial designed to test caloric restriction, not to validate the clocks.}[^lu2023]: `paper` Lu, A.T. et al. "Universal DNA methylation age across mammalian tissues." *Nature Aging*, 2023.[^lu2023]: `paper` Lu, A.T. et al. "Universal DNA methylation age across mammalian tissues." *Nature Aging*, 2023.[^johnson2025]: `statement` Johnson, B. "My Birthday Happens Every 2 Years." Blueprint blog, 2025. {Published on the store of Johnson's company, which sells the speed-of-aging test required to enter the leaderboard.}[^zimmer2025]: `news` Zimmer, C. (host). "The Truth About Biohacking." *The World As You'll Know It: The Future of Aging*, Aventine podcast, 2025. removed, struck through added, underlinedLine numbers count the serialised markdown of each revision, frontmatter included.
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