Biological Age

What biological age actually measures

Your birthday tells you how long you've been alive. Your biological age tells you how well your body has held up during that time. Two 50-year-olds can have radically different cardiovascular fitness, immune function, and cellular health. Biological age quantifies these differences using molecular and physiological markers, giving you a number that reflects how your organs, tissues, and cells are actually performing. For anyone serious about longevity, it's the single most useful metric for tracking whether your interventions are working.

How biological age is measured

The gold standard today is DNA methylation testing, commonly called epigenetic clocks. These tests analyze chemical modifications on your DNA (methyl groups attached to cytosine bases at specific CpG sites) that change predictably with age and health status. Steve Horvath published the first widely used multi-tissue clock in 2013, examining 353 CpG sites. It was accurate at predicting chronological age, but that turned out to be less useful than predicting health outcomes.

Second-generation clocks shifted focus from age prediction to mortality prediction. GrimAge, developed by Horvath and Ake Lu, incorporates plasma protein surrogates and smoking pack-years into its algorithm. It's one of the strongest predictors of all-cause mortality and disease risk available today ^[1]. PhenoAge, developed by Morgan Levine, combines DNA methylation data with nine clinical blood biomarkers to estimate biological age from a standard blood draw.

Third-generation clocks go further still. DunedinPACE (Pace of Aging Calculated from the Epigenome) doesn't estimate a static biological age. Instead, it measures how fast you are aging right now, expressed as biological years per calendar year. A DunedinPACE of 0.85 means you're aging at 85% of the average rate. This "pace" approach has proven more sensitive to lifestyle interventions than static age estimates ^[2].

Beyond DNA methylation

Telomere length, the protective caps on chromosome ends, was one of the earliest biological age markers. Each cell division shortens telomeres, and critically short telomeres trigger cellular senescence. However, telomere measurements have high variability between tests and limited predictive power for individuals ^[3]. Glycan age, based on IgG glycosylation patterns, offers another independent aging biomarker that responds to lifestyle changes within weeks. Composite blood panels (like the Klemera-Doubal method) calculate biological age from routine lab values and don't require specialized testing at all.

Can you change your biological age?

Yes, and the evidence is getting stronger. The CALERIE trial, a randomized controlled study of 220 non-obese adults, showed that 25% caloric restriction for two years slowed DunedinPACE by 2-3%, corresponding to a 10-15% reduction in mortality risk ^[2]. That effect size is comparable to quitting smoking.

A 2023 study by Fitzgerald et al. showed that six women following an 8-week methylation-supportive program (targeted nutrition, exercise, sleep optimization, stress management, and probiotics) reduced their biological age by an average of 4.6 years ^[4]. An earlier randomized trial by the same group found a 3.23-year decrease in DNAmAge compared to controls over eight weeks ^[5]. A 2024 study on fasting-mimicking diets reported measurable biological age reduction alongside metabolic and immune rejuvenation ^[6].

Exercise on its own moves the needle. Sedentary adults who adopted a structured 8-week exercise program (three 60-minute sessions per week) reversed about two years of biological aging. Combining aerobic and resistance training consistently associates with younger epigenetic age across studies.

How to test your biological age

For the most informative results, consider these points:

• DNA methylation tests (from providers like TruDiagnostic, epiAge, or neotes) give you multiple clock algorithms and DunedinPACE from a single saliva or blood sample
• Test at least twice, once as baseline and once after 3-6 months of interventions, to measure your rate of change rather than relying on a single snapshot
• Avoid testing during acute illness, severe stress, or immediately after drastic dietary changes, as these temporarily distort methylation patterns
• Complement epigenetic testing with regular blood panels (CRP, HbA1c, fasting insulin, lipids) for a fuller picture of how you're aging
• No single test captures everything. Combining 2-3 methods (e.g., epigenetic clock plus blood biomarkers plus a glycan test) gives the most reliable overall assessment