How Are Epigenetic Clocks Measured?

What Are Epigenetic Clocks?

Epigenetic clocks are composite biomarkers that estimate biological age from DNA methylation (DNAm) patterns at specific CpG sites across the genome. They are also referred to as DNA methylation age estimators, biological age clocks, or epigenetic age predictors. These clocks are typically built using penalized regression models—such as elastic net—that select a subset of CpG sites whose methylation levels correlate with chronological age in training cohorts. The output is a predicted age, often called DNAm age or epigenetic age. The difference between predicted age and chronological age is termed epigenetic age acceleration (EAA), which can be positive (older than expected) or negative (younger than expected).

Measurement is performed on DNA extracted from accessible tissues such as blood, saliva, or skeletal muscle. The most common platform is the Illumina Infinium MethylationEPIC array, which interrogates over 850,000 CpG sites, though older arrays like the 450K and 27K have also been used. The resulting methylation beta values (ranging from 0 to 1) are plugged into the clock's algorithm to produce an age estimate. The pathway or receptor family central to this work is not a single receptor but the broader epigenetic machinery—DNA methyltransferases (DNMTs), ten-eleven translocation (TET) enzymes, and the one-carbon metabolism pathway that supplies methyl donors.

Research Studies

Nicotinamide Riboside and Epigenetic Age Acceleration in Human Skeletal Muscle

A 2025 study examined the effects of 5-month nicotinamide riboside (NR) supplementation and 4–6 weeks of high-intensity interval training (HIIT) on epigenetic age acceleration in human skeletal muscle across three independent studies [1]. Seven epigenetic clocks were used to assess EAA. The authors reported that NR supplementation was associated with a reduction in EAA, while HIIT showed divergent effects depending on the clock used [1]. This suggests that different clocks may capture distinct aspects of epigenetic aging and that interventions can have clock-specific effects. The study was conducted in human participants, not animal models.

Seasonality and Biological Age Measurement in Adults

An ongoing clinical trial (NCT07242833) is investigating how seasonal variations influence biological age as measured by epigenetic clocks in adults [2]. The study aims to provide insights into the design and analysis of long-term lifestyle interventions targeting biological clocks. Biological age clocks can be measured from blood or saliva samples, and the trial will assess whether the pace of aging fluctuates with seasons [2]. This research is in human adults and highlights the importance of considering environmental factors when interpreting clock measurements.

Genetic Susceptibility to Epigenetic Age Acceleration in Asian Populations

A genome-wide association study (GWAS) of EAA using multiple epigenetic clocks was conducted in a Korean population to explore ethnic differences and individual variability [3]. The study identified Asian-specific genetic variants associated with EAA, underscoring that genetic architecture may influence clock readings differently across populations [3]. This finding is relevant for the interpretation of epigenetic clocks in diverse cohorts.

Comparison of Epigenetic Clocks

Different epigenetic clocks vary in their CpG composition, training datasets, and intended tissues. The table below summarizes key features of commonly used clocks, based on the evidence provided.

Note: The specific clocks used in the NR/HIIT study were not detailed in the available evidence, but seven clocks were employed [1].

Technical Variability in Epigenetic Clock Measurement

Measurement of epigenetic clocks involves several technical steps: DNA extraction, bisulfite conversion, array hybridization, and data normalization. Variability can arise from batch effects, tissue heterogeneity, and the choice of normalization method. The seasonality trial explicitly aims to enhance the design and analysis of long-term interventions by accounting for such variability [2]. Additionally, genetic factors can influence EAA, as shown in the Korean GWAS [3].

Epigenetic Clocks in Animal and In Vitro Models

While the evidence provided focuses on human studies, epigenetic clocks have been developed for animal models such as mice and rats. However, the available evidence does not include specific animal or in vitro studies of epigenetic clock measurement. Any extrapolation from animal clocks to human clocks should be made cautiously, as the CpG sites and training datasets differ.

Interpreting Epigenetic Age Acceleration

EAA is calculated as the residual from regressing DNAm age on chronological age. Positive EAA indicates that a sample appears older than expected, while negative EAA indicates it appears younger. In the NR/HIIT study, NR was associated with reduced EAA, suggesting a potential slowing of epigenetic aging in skeletal muscle [1]. However, the divergent effects of HIIT across clocks highlight that EAA is not a single unified metric but depends on the clock used [1].

Clinical and Research Applications

Epigenetic clocks are used in research to assess interventions, predict health outcomes, and study aging mechanisms. The seasonality trial is an example of applying clocks to understand environmental influences on biological age [2]. The GWAS in Korean populations demonstrates their use in genetic epidemiology [3]. These applications are for research purposes only and do not constitute medical advice.

If you are reading this for personal health reasons

The materials and information discussed here are sold for laboratory research use only. We do not provide dosing, medical guidance, or personal health recommendations. Anyone considering a compound or intervention for themselves should speak to a licensed clinician.

Sources

• [1] The Divergent Effects of Nicotinamide Riboside and High-Intensity Exercise Training on Skeletal Muscle Epigenetic Aging
• [2] Evaluation of the Effect of Seasonality on Biological Age in Adults
• [3] A genome-wide association study identifies Asian-specific genetic susceptibility for epigenetic age acceleration