What if your body were a different age than the one on your birth certificate? That is the whole premise of biological age, which reflects the real state of your body rather than the simple number of years elapsed. Long reserved for costly epigenetic tests, calculating it is now becoming accessible thanks to the Bortz method, based on a simple blood draw. More accessible, often more accurate, it relies on markers you can actually improve. Here is how, and above all, the values to aim for.
In brief – Biological age reflects the real physiological state of the body rather than the number of years since birth, and unlike chronological age, it can be improved. The Bortz method, published in 2023 in Communications Biology and built from UK Biobank data covering more than 300,000 people, estimates biological age from 25 common blood biomarkers, the kind found in a routine annual checkup. It predicts mortality risk with a concordance index of 0.778, edging out the reference PhenoAge blood model at 0.750, and rivals costly epigenetic clocks for a fraction of the price. Key markers include cystatin C, HbA1c, ApoB and high-sensitivity CRP, each with an optimal range that a doctor should help interpret, since many follow a U shaped curve where too low is as risky as too high. Retesting every six to twelve months, alongside lifestyle changes to diet, sleep and stress, can shift the numbers over time.
Biological Age: What Are We Talking About?
Chronological age counts the years since birth. Biological age, by contrast, measures the real wear on the body: two 50-year-old people can have the body of a 40-year-old or a 60-year-old. Concretely, it corresponds to the age of the same-sex population whose mortality risk matches yours.
The value of this is immense: unlike chronological age, it can be improved. Measuring it gives you a dashboard for your longevity, one capable of revealing a gap of up to twenty years, older or younger, compared with your actual age.
The Bortz Method: Biological Age From a Blood Test
Published in 2023 in the journal Communications Biology, part of the Nature group, the Bortz method was developed using the UK Biobank, a database of more than 300,000 people. Its principle: a statistical model combining 25 common blood biomarkers to estimate mortality risk, and by extension, one’s rate of aging.
Its great strength is that it uses standard blood tests, the kind often included in an annual checkup. A free calculator then delivers the result. Where biological age once seemed reserved for specialized laboratories, it is now within everyone’s reach.
Why It Rivals Epigenetic Tests, for Less Money
Epigenetic clocks, based on DNA methylation, have long been the reference standard. But they require specialized chips, often cost several hundred euros, and vary from one laboratory to another. The Bortz method, by contrast, relies on a standard blood test.
And its performance is impressive: it predicts mortality with a concordance index of 0.778, versus 0.750 for the reference blood model PhenoAge, an improvement of roughly 11% (PubMed data). It therefore rivals the best clocks for a fraction of the price. In fairness, epigenetic tests measure a different layer of aging biology (PubMed data) and keep their value in research. The main advantage of the Bortz method remains its combination of accessibility, accuracy and, above all, markers you can actually act on (scientific source).
The Tests to Run and Their Optimal Values
Here are the most decisive markers behind this score, with values that are not simply “normal” but optimal, meaning associated with the best longevity outcomes:
| Biomarker | What It Reflects |
|---|---|
| Cystatin C | Kidney function, the single most predictive marker |
| HbA1c | Glycation, average blood glucose over time |
| Fasting glucose | Glucose metabolism |
| Fasting insulin | Insulin sensitivity |
| High-sensitivity CRP | Chronic low-grade inflammation |
| ApoB | Arterial risk, more reliable than LDL |
| Gamma-GT | Liver function, oxidative stress |
| ALT | Liver function |
| Ferritin | Iron stores |
| Albumin | Nutritional and inflammatory status |
| Vitamin D (25-OH) | Vitamin D status |
| RDW | Variability in red blood cell size, an emerging aging marker |
- Cystatin C (kidney function, the single most predictive marker): about 0.6 to 0.9 mg/L.
- HbA1c (glycation, average blood glucose): under 5.4% (36 mmol/mol).
- Fasting blood glucose: 0.80 to 0.90 g/L (80 to 90 mg/dL, or 4.4 to 5.0 mmol/L), without aiming lower.
- Fasting insulin: under 6 microIU/mL.
- High-sensitivity CRP (inflammation): under 1 mg/L, ideally below 0.5.
- ApoB (arterial risk, more reliable than LDL): under 0.80 g/L (80 mg/dL).
- Gamma-GT (liver, oxidative stress): under 25 U/L.
- ALT (liver): under 25 U/L in women, 30 U/L in men.
- Ferritin (iron stores): 30 to 100 micrograms per liter (30 to 100 ng/mL), neither deficient nor overloaded.
- Albumin: 45 to 50 g/L (4.5 to 5.0 g/dL), in the upper part of the range.
- Vitamin D (25-OH): 40 to 60 ng/mL (100 to 150 nmol/L).
- RDW (red blood cell size variability): under 13%.
Watch out for a major trap: an “optimal” value is a point of balance, not an extreme. Many of these markers follow a U shaped curve, where too low is just as harmful as too high. An ideal fasting glucose sits around 0.85 g/L (85 mg/dL), not 0.50. These targets, stricter than standard laboratory norms, must therefore be interpreted by a doctor, never pushed blindly.
How to Interpret the Results and Take Action
Knowing this number is only useful if you act on it. The good news is that these markers respond to the same levers as longevity itself:
- Retest regularly: every six to twelve months, to track the trend rather than a single number.
- Work on lifestyle: physical activity, sleep, stress management and diet influence most of these markers.
- Optimize your nutrition: controlling sugar intake, getting enough protein, and eating a diet rich in plants.
- Support cellular vitality: for example, by taking care of your NAD+ levels.
This approach fits squarely within the major levers of longevity: the test measures, lifestyle transforms.
Frequently Asked Questions
What exactly is the Bortz method?
It is a scientific model published in 2023 that estimates biological age from 25 common blood biomarkers. Developed using data from more than 300,000 people, it predicts mortality risk slightly better than the reference blood model, based on a simple blood test.
Is it really more accurate than epigenetic tests?
For predicting mortality, the Bortz method rivals the best clocks, at a much lower cost. Epigenetic tests, however, measure a different aspect of aging and remain useful, particularly in research.
What is the difference between a normal value and an optimal value?
A “normal” value simply means it falls within the population average. An “optimal” value aims for the best possible longevity, and is often stricter. Be careful: optimal does not mean extreme, since many markers follow a U shaped curve.
Where can you get these tests done?
Most of these markers are included in a standard blood panel ordered by a doctor. Some, such as cystatin C or ApoB, sometimes need to be requested specifically. Interpretation is best done with a healthcare professional.
Medical disclaimer. The information provided here is for informational purposes only and does not constitute medical advice. It does not replace a consultation. Ask a healthcare professional before changing your diet, taking dietary supplements or starting a new practice, especially if you have a medical condition, are pregnant or are under treatment. Dietary supplements do not replace a balanced diet or medical follow-up.
