What if your body were a different age than the one on your ID card? That is the whole point of biological age, which reflects the real state of your body rather than the simple number of years since birth. Long reserved for costly epigenetic tests, calculating it is becoming accessible thanks to the Bortz method, built on a standard blood draw. More affordable and often more precise, it relies on markers you can actually act on. Here is how it works, and above all, the values to aim for.
In brief – Biological age reflects how worn your body actually is, rather than the years since birth: two 50 year olds can carry the body of a 40 year old or a 60 year old. Published in 2023 in the Nature group journal Communications Biology, the Bortz method estimates this biological age from 25 common blood biomarkers, using data from more than 300k people in the UK Biobank. It predicts mortality risk with a concordance index of 0.778, an improvement of about 11% over the reference blood model PhenoAge, at a fraction of the cost of an epigenetic clock. Markers such as cystatin C, HbA1c, ApoB and high sensitivity CRP each have an optimal range, generally stricter than standard lab norms, that should be interpreted with a doctor rather than pushed to an extreme.
Biological age: what does it actually mean?
Chronological age counts the years since birth. This other measure, by contrast, reflects the real wear on the body: two people aged 50 can have the body of a 40 year old or a 60 year old. In practice, it corresponds to the age of the same sex population whose mortality risk matches your own.
The value of this measurement is considerable: unlike chronological age, biological age can be improved. Measuring it produces a longevity dashboard capable of revealing a gap of up to twenty years, higher or lower, compared with your actual age.
The Bortz method: biological age from a blood test
Published in 2023 in the Nature group journal Communications Biology, the Bortz method was developed using the UK Biobank, a database of more than 300k people. Its principle is a statistical model that combines 25 common blood biomarkers to estimate mortality risk, which in turn yields this age estimate.
Its main strength is that it relies on standard blood panels, the kind often included in an annual checkup. A free calculator then converts the results into a score. Where this kind of test once seemed reserved for specialized laboratories, it is now within reach of anyone with a routine blood test.
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 dollars, and vary from one laboratory to another. The Bortz method, by contrast, relies on a standard blood draw.
Its performance is striking: it predicts mortality with a concordance index of 0.778, against 0.750 for the reference blood model PhenoAge, an improvement of roughly 11% (PubMed data). It therefore rivals the best clocks at a fraction of the price. In fairness, epigenetic tests measure a different layer of aging biology (PubMed data) and keep their value in research settings. The main advantage of the Bortz method remains its combination of accessibility, precision, and above all, markers you can actually act on (scientific source).
The tests to take and their optimal values
Below are the most determining markers behind this score, listed not with simple “normal” ranges but with optimal values, meaning the ranges associated with the best longevity outcomes:
| Biomarker | What it reflects | Optimal value |
|---|---|---|
| Cystatin C | Kidney function, the single most predictive marker | About 0.6 to 0.9 mg/L |
| HbA1c | Glycation, average blood glucose | Below 5.4% (36 mmol/mol) |
| Fasting glucose | Blood sugar regulation | 0.80 to 0.90 g/L (4.4 to 5.0 mmol/L, about 80 to 90 mg/dL), without aiming lower |
| Fasting insulin | Insulin sensitivity | Below 6 uIU/mL |
| High sensitivity CRP | Inflammation | Below 1 mg/L, ideally under 0.5 |
| ApoB | Arterial risk, more reliable than LDL | Below 0.80 g/L (about 80 mg/dL) |
| Gamma GT | Liver function, oxidative stress | Below 25 U/L |
| ALT | Liver function | Below 25 U/L in women, 30 U/L in men |
| Ferritin | Iron stores | 30 to 100 ug/L, neither deficient nor overloaded |
| Albumin | Protein status | 45 to 50 g/L (4.5 to 5.0 g/dL), upper part of the range |
| Vitamin D (25 OH) | Vitamin D status | 40 to 60 ng/mL (100 to 150 nmol/L) |
| RDW | Variability in red blood cell size | Below 13% |
A key trap to avoid: 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, not 0.50 g/L. These targets, stricter than standard lab reference ranges, should therefore be interpreted by a doctor and never pushed blindly.
How to interpret and act on your results
Knowing this number only matters if you use it to improve. The good news is that these markers respond to the same levers that drive longevity itself:
- Retest regularly: every six to twelve months, to track the trend rather than a single isolated number.
- Work on lifestyle: physical activity, sleep, stress management and diet influence most of these markers.
- Optimize nutrition: controlling sugar intake, getting enough protein and eating a plant rich diet.
- Support cellular vitality: for example, by looking after your NAD+ levels.
This approach fits squarely within the broader pillars of longevity: the test measures, and 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 300k people, it predicts mortality risk slightly better than the reference blood model, based on a single standard blood draw.
Is it really more precise than epigenetic tests?
For predicting mortality, the Bortz method rivals the best epigenetic clocks, at a much lower cost. Epigenetic tests, however, measure a different aspect of aging and keep their usefulness, 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 targets the best possible longevity outcome, and is often stricter. Note that optimal does not mean extreme, since many markers follow a U shaped curve.
Where can these tests be done?
Most of these markers appear on a standard blood panel prescribed by a doctor. Some, such as cystatin C or ApoB, may need to be requested specifically. Interpretation is best done together 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.
