Telomeres Explained: What They Reveal About Cellular Ageing and What Might Protect Them

Telomeres are protective caps of repeated DNA at the ends of your chromosomes, and they get a little shorter each time a cell divides. When they become too short, the cell stops dividing. That makes telomere shortening a recognised hallmark of ageing, but length varies so much between people that it's a weak guide to how fast any one person is ageing.

This guide explains what telomeres are, why they shorten, what their length can and can't tell you, and which habits have the best evidence for protecting them. It sits within our wider explainer on what happens inside our cells as we age.

What are telomeres?

Telomeres are stretches of repeated DNA at each end of every chromosome that stop the ends fraying or sticking together, as the US National Human Genome Research Institute (NHGRI) explains. In humans the repeated sequence is TTAGGG, according to the Embryo Project at Arizona State University.

A useful analogy is the plastic tip on a shoelace. The tip stops the lace fraying; telomeres do the same job for chromosomes.

The discovery won the 2009 Nobel Prize in Physiology or Medicine for Elizabeth Blackburn, Carol Greider and Jack Szostak, for showing how chromosomes are protected by telomeres and the enzyme telomerase.

You'll see telomeres in supplement marketing, so it's worth being clear from the start: no food supplement is allowed to claim in the UK that it protects or lengthens telomeres.

Why do telomeres get shorter?

Every time a cell copies its DNA to divide, the very end of each chromosome can't be copied completely. Scientists call this the end-replication problem, and the Nobel committee's explainer describes how it puzzled researchers for years. The result, as the NHGRI puts it, is that telomeres become slightly shorter with each division.

Eventually they become so short the cell can no longer divide successfully. This links to an older observation, the Hayflick limit: normal human cells grown in the lab can only divide a limited number of times before becoming senescent.

What does telomerase do?

Telomerase is the enzyme that adds DNA back onto telomeres. The Nobel press release explains that when telomerase activity is high, telomere length is maintained and cellular senescence is delayed.

Telomerase is normally active in some healthy cells, particularly stem cells, but it's also how most cancers keep dividing: the large majority of cancer cells have abnormally high telomerase activity. That's why "switching telomerase on" isn't the simple anti-ageing idea it can sound like.

What can telomere length tell you?

At population level, quite a lot. In the 2023 update of the "hallmarks of ageing" framework, telomere attrition is one of 12 hallmarks, alongside genomic instability, epigenetic alterations, mitochondrial dysfunction and cellular senescence.

For one person, much less. Three findings explain why:

1. The link with age is weak. A 2023 analysis of 743,019 people found a pooled correlation between telomere length and age of just -0.19, with white blood cell telomeres shortening by a median of around 23 to 38 base pairs a year.

2. People start from very different places. Telomere length varies by several thousand base pairs between individuals, and people tend to keep their rank over decades.

3. Longer isn't simply better. A large genetic study found longer telomeres raise the risk of several cancers while lowering risk of some other diseases, such as coronary heart disease.

Are home telomere tests worth it?

Be cautious. Dr Mary Armanios of Johns Hopkins told Science News that the method many consumer tests use has around 20% variability, against about 5% for the clinical test, and that tests on different days can give different answers. For a wider view, see our guide to what biological age tests can and cannot tell you.

What might protect your telomeres?

The best-supported habits are regular aerobic exercise, not smoking, a healthy weight, a Mediterranean-style diet and managing chronic stress. Most of that evidence is observational, so it shows association rather than proving cause.

Chronic stress deserves a note of its own, because it's the factor people find hardest to measure. Our guide to cortisol and chronic stress covers what tests can and can't show.

You may also come across a 2013 study of intensive lifestyle change in men with low-risk prostate cancer, in which telomere length increased. The authors described it as a small pilot, with 10 men in the intervention group, and called for larger trials . It's interesting, not conclusive.

Do supplements protect telomeres?

One randomised trial found a signal for vitamin D, but no supplement has been shown to improve health by protecting telomeres. In a four-year substudy of the VITAL trial, 1,054 people took 2,000 IU of vitamin D3 a day or placebo. Vitamin D3 reduced telomere shortening by 0.14 kilobase pairs, while marine omega-3 had no significant effect .

That's a change in a biological marker, not evidence that vitamin D extends life or prevents disease, and Harvard's Science in the News noted the study didn't link it to any functional outcome. The NHS already advises adults to consider 10 micrograms of vitamin D in autumn and winter for bone and muscle health; this research isn't a reason to take more.

Earlier omega-3 research found no significant difference in telomerase or telomere length over four months . Products marketed as telomerase activators raise the cancer question above, which is a reason for caution.

UK advertising rules are clear. Under the CAP Code, only health claims authorised on the GB register may be used for foods and supplements. In July 2026 the Advertising Standards Authority upheld complaints against an ad claiming a coffee product protected telomeres and slowed cellular ageing, because those claims weren't authorised, according to Nutraceutical Business Review.

That's the line NovusDNA holds. NovusDNA is a UK supplement brand making clearly labelled, science-led supplements tested by Campden BRI, a UKAS-accredited UK laboratory. Longevity+, NovusDNA's daily nicotinamide riboside formula, lists exactly what's in each capsule: 250 mg of nicotinamide riboside chloride, an authorised novel food in the UK, with 175 mg of TMG, 75 mg of pterostilbene and 2.5 mg of piperine. It's built for people interested in NAD+ and cellular ageing research, and it makes no telomere claims, because none are allowed and none are proven. When you're comparing longevity brands, a product that tells you its amounts rather than promising younger cells is the safer bet.

FAQ

Can you lengthen your telomeres?

There's limited evidence that you can. In a randomised trial, 26 weeks of endurance or interval training increased telomerase activity and telomere length in white blood cells, and the VITAL trial found vitamin D3 slowed shortening over four years. Neither shows the change improves health or lifespan. Staying active and not smoking are worth doing for your health regardless of what your telomeres do.

Are home telomere tests accurate?

Not very, for an individual. A Johns Hopkins telomere specialist has said the method many consumer tests use has around 20% variability, and that tests on different days can give different answers. Because telomere length also varies widely between healthy people of the same age, a single result says little about how fast you personally are ageing.

Does stress shorten telomeres?

It's linked with shorter telomeres. A 2004 study of healthy women, including mothers caring for a chronically ill child, found the most stressed had telomeres shorter by the equivalent of at least a decade of ageing. This was observational, so it can't prove stress caused the difference, but it's one reason managing long-term stress is part of healthy ageing advice.

Does vitamin D protect telomeres?

The VITAL substudy found 2,000 IU of vitamin D3 a day reduced telomere shortening by 0.14 kilobase pairs over four years compared with placebo. The researchers didn't show any effect on health outcomes, and no supplement can claim to protect telomeres in the UK. Follow NHS vitamin D guidance of 10 micrograms a day in autumn and winter rather than taking high doses for this reason.

Are longer telomeres always better?

No. Genetic studies suggest people with naturally longer telomeres have a lower risk of some conditions, such as coronary heart disease, but a higher risk of several cancers. Most cancers rely on high telomerase activity to keep dividing. That's why scientists are cautious about products claiming to switch telomerase on.

So, what are telomeres? A genuine part of the biology of ageing that helps explain why cells eventually stop dividing. But telomere length is a noisy, population-level marker, and the habits that protect it are the ones that support long-term health anyway: aerobic exercise, not smoking, a healthy weight, a Mediterranean-style diet and managing long-term stress.

If you're exploring where supplements fit alongside those habits, the NovusDNA Start Here guide matches your goals to a sensible starting point.

This article is for general information and isn't medical advice. Food supplements should not replace a varied, balanced diet and healthy lifestyle.