Your Body Has Two Different Ages
You have a chronological age, the number of birthdays you have had. But you also have a biological age, which reflects how worn or well-maintained your cells actually are. Two 65-year-olds can be the same on paper yet decades apart inside. For most of history we had no real way to measure that inner age. In the last decade, a technology called the epigenetic clock has changed that. By reading chemical marks on your DNA, these tests aim to estimate your biological age, and the newest versions claim to show how fast you are aging right now.
What Epigenetic Clocks Actually Read
<strong>Curious about your own number?</strong> realBioAge.com estimates your true biological age in minutes from simple, science-based inputs — then shows you what's aging you faster and what to do about it. <a href="https://realbioage.com" target="_blank" rel="noopener">Take the realBioAge test →</a>
Epigenetic clocks do not read the genes you inherited. They read a layer of chemistry sitting on top of your DNA called DNA methylation. Methylation happens when a small chemical tag, a methyl group, attaches to a specific spot on the genome, usually where a cytosine sits next to a guanine, a location scientists call a CpG site. These tags can switch nearby genes on or off without changing the underlying genetic code, according to a review in Pharmacology and Therapeutics housed at the NIH's National Library of Medicine.
Crucially, methylation patterns drift as we age in a surprisingly predictable way. Only a small share of sites, roughly 2 percent, change with age, but because the human genome is so large, that still amounts to two to three million spots, the same NIH-archived review notes. Some sites gain methylation over the years while others lose it. By measuring just a few hundred carefully chosen CpG sites, researchers can read those changes like the rings of a tree and estimate age with striking accuracy.
The Horvath Clock: The First Big Breakthrough
The field began in earnest in 2013, when Steve Horvath of UCLA published a landmark paper in the journal Genome Biology. Horvath built a multi-tissue clock using more than 8,000 samples across dozens of human tissues and cell types, and distilled the signal down to 353 specific methylation sites, as described in his paper (Genome Biology, 2013) and summarized by the Max Planck Institute for Biology of Ageing. The fact that one formula worked across blood, brain, liver, and many other tissues made it the first truly general-purpose biological clock.
How accurate is it? Horvath's clock predicted a person's chronological age with a median error of about 3.6 years and a correlation of roughly 0.96, meaning predicted age and real age line up very closely, according to his original report and the Wikipedia overview of epigenetic clocks that cites it. A separate 2013 clock by Gregory Hannum's team at UC San Diego used 71 sites in blood and reached similar accuracy, making both foundational first-generation clocks.
Second-Generation Clocks: From Age to Health
First-generation clocks like Horvath and Hannum were trained to match birthday age. But a clock that simply predicts your age is not as useful as one that predicts your health. That insight drove the second generation. In 2018, Morgan Levine, then at UCLA, and colleagues published DNAm PhenoAge in the journal Aging. Instead of training on chronological age alone, they blended in nine clinical markers, such as blood sugar and measures of liver, kidney, and immune function, then found 513 methylation sites that captured that phenotypic picture, as reported in the study and summarized in a peer-reviewed systematic review in Aging.
The payoff is prediction. PhenoAge has been shown to forecast mortality, cancer, physical decline, and even Alzheimer's risk better than chronological age, according to the same systematic review in Aging and the University of Michigan Health and Retirement Study epigenetic clocks documentation. In short, a person whose PhenoAge runs ahead of their birthday age is, statistically, at higher risk, even if they feel fine today.
GrimAge: Built to Predict Lifespan
The clock that has drawn the most attention for predicting how long people live is GrimAge, developed by Ake Lu, Steve Horvath, and colleagues and published in Aging in 2019. Rather than tracking age directly, GrimAge combines methylation-based estimates of eight blood proteins linked to disease, plus a methylation signature of smoking history, as detailed in the original paper and a Nature Translational Psychiatry study that used the measure. The name is deliberately blunt: high values signal grim news for mortality and morbidity risk.
When researchers at the U.S. National Institute on Aging compared the major clocks head to head, GrimAge outperformed PhenoAge, the Horvath and Hannum clocks, and DunedinPACE at predicting death, according to that NIA comparison. A separate 18-year follow-up of older female twins, published in Clinical Epigenetics, found GrimAge predicted mortality even after accounting for shared genetics, adding confidence that the signal is real and not just inherited.
DunedinPACE: A Speedometer, Not an Odometer
The clocks above act like an odometer, estimating total mileage. DunedinPACE works more like a speedometer, estimating how fast you are aging right now. Developed by Daniel Belsky of Columbia University with the Moffitt and Caspi team at Duke, it was published in the journal eLife in 2022. The researchers tracked 19 measures of organ health across two decades in New Zealand's Dunedin birth cohort, then distilled that long-term pace of aging into a single blood test, as described in the eLife paper and on Duke University's Moffitt and Caspi research site.
DunedinPACE is reported in years of biological aging per calendar year. A value of 1.0 means you are aging at the expected pace of one biological year per year; above 1.0 means faster, below 1.0 means slower, per the eLife study and Duke's project description. Because it captures current pace, it is especially appealing for testing whether a diet, exercise plan, or medication is slowing aging in real time. The measure has now been validated in dozens of cohorts across many countries and ancestry groups.
How Much Should You Trust the Number?
エピジェネティック時計は、科学が生み出した生物時代のツールの中で最も再現性が高いものの 1 つですが、実際には限界があります。結果は、検査した組織、検査方法、さらには時間帯や最近の病気によっても変わる可能性があり、1 回の測定値は、正確な判断というよりは、誤差の範囲内での推定値として理解するのが最も適切です。この時計は主に血液サンプルと完全に多様性が満たされていない集団に基づいて構築されたため、一部のグループでは精度が低くなる可能性があります。また、個人の運命ではなく、集団全体のリスクについても教えてくれます。 |||9月||| 50 歳以上の人々にとって、実践的な教訓は励みとなり、根拠のあるものです。健康的な老化に長い間結びついてきた同じライフスタイル要因、つまり禁煙、活動的な生活、よく眠る睡眠、体重と血糖値の管理が、まさにこれらの時計が拾う信号なのです。研究者らは介入によって時計の針を戻せるかどうかを積極的に研究しており、初期の結果は有望だがまだ確定していない。消費者向けエピジェネティック検査を受けることを選択した場合は、結果を全体像の中の 1 つのデータ ポイントとして扱い、それを背景に置くことができる臨床医に提出してください。 |||9月||| この記事は教育的なものであり、医学的なアドバイスではありません。健康状態や検査については医師に相談してください。 |||9月||| 遺言で家族を守る |||9月||| オンラインで数分で遺言書または生前信託を作成できます。弁護士支援のオプションは 89 ドルから。 |||9月||| 不動産計画を始める
For people over 50, the practical takeaway is encouraging and grounded. The same lifestyle factors long tied to healthy aging, not smoking, staying active, sleeping well, and managing weight and blood sugar, are the very signals these clocks pick up. Researchers are actively studying whether interventions can turn the clocks back, and early results are promising but not yet settled. If you choose to take a consumer epigenetic test, treat the result as one data point in a bigger picture, and bring it to a clinician who can put it in context.
<strong>Curious about your own number?</strong> realBioAge.com estimates your true biological age in minutes from simple, science-based inputs — then shows you what's aging you faster and what to do about it. <a href="https://realbioage.com" target="_blank" rel="noopener">Take the realBioAge test →</a>
This article is educational and not medical advice. Talk with your doctor about your health and any testing.