Longevity guide

Measuring biological age: what tests can and cannot do

Reviewed by Dr. Daniel Wallerstorfer, molecular biologist and founder of Novogenia · Updated: 12 October 2026 · Reading time: 9 min

In short

People of the same age age at different speeds – and research can now make this visible. Epigenetic clocks, telomere length and combinations of body measures each capture their own facet of aging. Especially exciting: in a randomized trial, two years of calorie restriction slowed the pace of aging as measured by an epigenetic clock – a sign that lifestyle matters. Novogenia does not offer a biological-age measurement; genetic analyses describe predispositions that remain valid for life.

Same age – yet aging at different speeds

You know the feeling: two people were born in the same year, yet one looks much younger than the other. Research can now measure this impression. The Dunedin Study in New Zealand followed 954 young adults across three measurement points in their 20s and 30s, assessing the lungs, gums, cardiovascular system, kidneys, liver and immune system. The result: even before midlife, people of the same age were aging at different speeds. Those who aged faster were less physically capable, rated their own health as worse and looked older (Belsky et al., PNAS, 2015).

That is the idea behind biological age: making visible how far aging processes have progressed in the body – regardless of the date in your passport. Here you will learn which methods exist, what they show, and what you can conclude from them for your offer.

What “biological age” actually means

Your chronological age is on your passport. Your biological age is an estimate of how far aging processes have progressed in your body. How valuable such estimates can be is shown by a study that compared five methods in 9,389 people aged 30 to 75 who were followed for 18 years. The best method predicted mortality more reliably than chronological age (Levine, Journals of Gerontology A, 2013).

It is also fascinating that there is no single number. In the Dunedin Study, eleven measures of biological aging were compared in 964 middle-aged people: telomere length, epigenetic clocks and combinations of body measurements. The measures agreed only a little – they apparently capture different facets of aging. One epigenetic clock and the combinations of body measurements were consistently linked to signs of aging such as physical functioning and facial appearance (Belsky et al., American Journal of Epidemiology, 2018).

Epigenetic clocks: sticky notes in the recipe book

Your DNA is a very long recipe book. The recipes themselves do not change over your lifetime. What does change are small chemical marks – methyl groups – that act like sticky notes showing which recipes are currently being read. With age, the pattern of these sticky notes shifts in a remarkably predictable way. Epigenetic clocks read this pattern and convert it into an age.

The best-known clock dates from 2013. It was developed with 8,000 samples from 51 healthy tissues and cell types and uses 353 measurement sites in the genome. A fascinating detail: for embryonic stem cells, its value is close to zero (Horvath, Genome Biology, 2013). Shortly before, a clock based on blood samples from 656 people aged 19 to 101 was published (Hannum et al., Molecular Cell, 2013).

The field has evolved rapidly since then, and a picture from the car helps to sort it out. The first clocks are like the odometer: they were trained to match calendar age as closely as possible. Newer clocks such as PhenoAge and GrimAge are geared toward health data and life expectancy (Levine et al., Aging, 2018). GrimAge stands out for its ability to predict life expectancy and shows the expected relationship with lifestyle factors such as a healthy diet (Lu et al., Aging, 2019). And DunedinPACE is like a speedometer: it estimates how fast someone is aging right now, gives very stable values in repeat measurements, and is linked to disease, disability and mortality (Belsky et al., eLife, 2022).

Telomeres: the caps on a shoelace

Telomeres are the protective caps at the ends of your chromosomes – like the plastic tips at the ends of shoelaces. They get a little shorter with every cell division.

That telomeres in white blood cells get shorter with age is well established. A systematic review of 124 cross-sectional and 5 longitudinal studies estimates the loss at 24.7 base pairs per year (Müezzinler et al., Ageing Research Reviews, 2013). How well telomere length works as a stand-alone measure of a person’s age is something research is still examining (Mather et al., Journals of Gerontology A, 2011).

There is a lot to take away for practice. The telomere-protective basics include not smoking, limiting UV exposure and a lifestyle that keeps oxidative and inflammatory load in check. How genes play a part is shown in the gene story Telomeres and the genetics of skin renewal.

Combined body measures: the dashboard

A third approach combines values that medicine measures anyway – for the lungs, the cardiovascular system, the kidneys, the liver and the immune system. On its own, each value says little about aging. Together, they form a dashboard that shows the state of several organ systems at once.

That is exactly how the Dunedin Study from the beginning of this article worked. The big advantage: the dashboard stays close to how the organs actually function. The PhenoAge clock builds on the same idea – it was developed using such clinical values and then translated into a methylation pattern (Levine et al., 2018).

The three approaches compared

Approach	What is measured	What it shows	What you can conclude
Epigenetic clocks	DNA methylation patterns, often from blood	the pace and stage of aging; newer clocks predict health risks and life expectancy	aging is a measurable, dynamic process linked to lifestyle
Telomere length	length of chromosome ends, usually in white blood cells	how often cells have divided	not smoking, sun protection and a balanced lifestyle as the basics
Combined body measures	several measurements combined into an index	the state of several organ systems at once	fitness, blood pressure or blood values are valuable progress markers on their own, too

Lifestyle and the pace of aging

Perhaps the most exciting question is: can the pace of aging be influenced? The CALERIE trial is one of the first randomized trials to examine this with epigenetic clocks. 220 adults without obesity were randomly assigned either to a group that was to cut calorie intake by 25% for two years or to a control group without restrictions. The result: calorie restriction slowed the pace of aging as measured by DunedinPACE. The effects were small – but according to the authors, even a modest slowing can mean a great deal for population health (Waziry et al., Nature Aging, 2023). PhenoAge and GrimAge did not change significantly – further evidence that the clocks capture different facets of aging.

To make such before-and-after comparisons meaningful for individuals too, research is working hard on precision. Technical noise had caused deviations of up to 9 years between repeat measurements of the same sample for six well-known clocks. With an improved computational method, most repeat measurements agreed within 1.5 years (Higgins-Chen et al., Nature Aging, 2022).

For counseling, this means: research on biological age provides a strong argument for lifestyle. What large studies show about exercise, sleep and nutrition is covered in Lifestyle first.

Biological age in your offer: what to look for

Biological-age tests are a strong conversation starter: one number, an aha moment, a reason for the next appointment. If you want to offer such a test, these questions help you find a good partner:

Which method and which clock does the provider use – and has it been published in scientific journals?
How well do repeat measurements of the same sample agree?
Which lab performs the measurement, and to which quality standards?
Is the result explained as an estimate, with a view to the facet of aging it captures?
What happens after the test: is there counseling and a plan?
Are the advertising claims clean? Promises that a product or program makes people biologically younger are not supported and are legally risky (more in Advertising longevity).

Frame the result as a snapshot that raises questions and opens a conversation. A sentence that fits: “This value is an estimate from research. It shows a tendency, and we will look at it together with your training, your sleep and your diet.” And avoid rankings or comparisons between employees: health data belong to the person who was tested.

What Novogenia offers – and what it does not

Novogenia does not offer a biological-age measurement. Our genetic analyses read genes from a saliva sample. These genes do not change over a lifetime – so they cannot show how far someone has aged. Their strength lies elsewhere: they describe predispositions, that is, how your body handles nutrients, training or stress, and they remain valid for life.

One example is the telomere chapter of the Beauty analysis. It shows your TERT and PPARG genes, which are linked to the pace of cellular skin aging – but it does not measure the length of your telomeres.

For your offer, this means: genetic analyses make a longevity offer personal. Progress is measured with what changes: strength, endurance, sleep, weight – or blood values measured by physicians. What this looks like in the gym is shown in Genetics in training.

Frequently asked questions

What is an epigenetic clock?

A computational model that estimates age from chemical marks on DNA, the methyl groups. The best-known clock dates from 2013. Newer clocks are geared toward health data and life expectancy, or estimate the pace of aging – like a speedometer instead of an odometer.

What do biological-age tests show?

In large studies, they make visible that people age at different speeds, and newer clocks predict health risks and life expectancy. For an individual, they are an estimate. Research is working hard on precision: with an improved method, most repeat measurements agreed within 1.5 years.

What does telomere length say about age?

Telomeres get shorter with age, by an average of 24.7 base pairs per year. Research is still examining how well telomere length works as a stand-alone measure. In practice, not smoking, sun protection and a lifestyle that keeps oxidative and inflammatory load in check are what count.

Can a genetic analysis determine biological age?

No. Genes do not change during a lifetime, so they cannot show how far someone has aged. Genetic analyses describe predispositions. Novogenia does not offer a biological-age measurement.

Can I advertise with biological age?

Be careful. Claims that a product or service makes people biologically younger are not supported and are legally risky. If you offer a test, explain the result as an estimate. More in the chapter “Advertising longevity.”

Want to add longevity to your offer?

Tell us about your gym, company or practice – we will show you what is possible today.

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Note: This guide is general information for businesses and professionals and does not replace medical or legal advice. Novogenia longevity products are food supplements and not a substitute for a balanced, varied diet and a healthy lifestyle; statements in this guide are not promises of cure and not statements on the prevention, treatment or healing of diseases. Recommendations derived from genetic analyses are logical conclusions, not scientifically proven. Regulations can change; errors and changes excepted.