Telomeres are protective caps of repeated DNA at the ends of your chromosomes. They shorten a little each time most cells divide, and when they get too short the cell stops dividing. That's why telomere length is studied as a marker of cellular aging, though a single telomere test says less about your health than many ads suggest.
Research on telomeres won the 2009 Nobel Prize in Physiology or Medicine, and they've been a favorite topic in aging research ever since. This guide explains what telomeres and telomerase are, why telomeres shorten, what telomere length can and can't tell you, and which everyday habits studies have linked to longer telomeres.
Last reviewed: November 12, 2026
Key Takeaways
- Human telomeres are typically 10,000 to 15,000 DNA base pairs long and lose an estimated 50 to 250 base pairs each time a cell divides.
- Normal human cells grown in a lab stop dividing after about 40 to 60 divisions, a cutoff known as the Hayflick limit.
- In a 6-month randomized trial, endurance and interval training raised telomerase activity two- to threefold in blood cells; strength training alone didn't.
- Telomere length varies widely between people of the same age, so it isn't a precise clock.
- Longer isn't automatically better: a large 2017 genetic study found trade-offs in both directions.
What are telomeres?
Telomeres are stretches of a short DNA sequence, TTAGGG, repeated thousands of times at the end of each chromosome. A group of proteins called shelterin binds to them and keeps the cell from mistaking the chromosome end for broken DNA. Human telomeres typically range from 10,000 to 15,000 base pairs long (Srinivas et al., 2020).
A common comparison is the plastic tip on a shoelace: it doesn't carry information itself, but it stops the lace from fraying. Elizabeth Blackburn, Carol Greider and Jack Szostak shared the 2009 Nobel Prize for discovering how telomeres and the enzyme telomerase protect chromosomes (Nobel Prize, 2009).
Why do telomeres get shorter with age?
Telomeres get shorter because the machinery that copies DNA can't copy the very end of a chromosome. Each time a cell divides, a small piece of telomere is lost, an estimated 50 to 250 base pairs per division (Srinivas et al., 2020). Oxidative damage and other stresses can speed up the loss.
In 1990, researchers showed that telomeres in human skin cells called fibroblasts got shorter as the cells were grown and divided in the lab (Harley et al., 1990). Normal human cells in culture stop dividing after about 40 to 60 divisions, known as the Hayflick limit, and telomere shortening acts as the counter. When telomeres become too short, the cell enters a state called replicative senescence (Srinivas et al., 2020). Our guide to senescent cells explains what happens next.
What is telomerase?
Telomerase is the enzyme that adds TTAGGG repeats back onto telomeres. It's active in cells that need to keep dividing for a long time, and it slows telomere loss in fast-renewing tissues such as blood-forming cells, skin and the gut lining. Most adult stem cells and body tissues don't make enough telomerase to keep telomeres at full length forever, so telomeres shorten with age (Srinivas et al., 2020).
Telomerase isn't simply good. Cells that keep it switched on can keep dividing without the usual limit (Srinivas et al., 2020). That's one reason scientists are cautious about the idea of turning it up in the whole body.
What does telomere length tell you about aging?
Telomere length is linked to age and survival on average, but it's a weak predictor for any one person. In an early study of 143 people over 60, those with shorter telomeres in their blood cells had poorer survival over the following years (Cawthon et al., 2003). Later reviews found the picture messier. A 2013 review of epidemiology studies concluded that shorter blood telomere length is consistently tied to older age and male sex, but that links with other health measures are mixed. The authors point to differences in how labs measure telomeres as one reason studies disagree (Sanders and Newman, 2013).
Longer telomeres aren't automatically better either. A 2017 genetic study that pooled data from more than 400,000 cases found that people born with genetically longer telomeres had a higher risk of several serious health problems and a lower risk of others, including some heart problems (Telomeres Mendelian Randomization Collaboration, 2017). That's why "longer is better" is too simple.
| Question | What the research shows | Source |
|---|---|---|
| Do telomeres shorten with age? | Yes, on average, in blood and many tissues | Srinivas et al., 2020; Sanders and Newman, 2013 |
| Is short telomere length linked to survival? | Shorter blood telomeres went with poorer survival in people over 60 | Cawthon et al., 2003 |
| Is telomere length a precise aging clock? | No. It varies a lot between people of the same age, and results depend on the lab method | Sanders and Newman, 2013; Srinivas et al., 2020 |
| Are longer telomeres always better? | No. Genetically longer telomeres raised some risks and lowered others | Telomeres Mendelian Randomization Collaboration, 2017 |
If you're thinking of buying a telomere test, our guide to biological age tests compares what different tests actually measure.
Can exercise lengthen telomeres?
One randomized trial suggests endurance exercise can. Researchers assigned 124 healthy, previously inactive adults to 6 months of continuous running, high-intensity interval training, strength training on 8 machines, or no change, with three 45-minute sessions a week. Telomerase activity in blood immune cells rose two- to threefold in both endurance groups, and telomere length in several types of white blood cells increased. The strength-training group didn't see these changes, even though all three exercise groups improved their fitness (Werner et al., 2019).
That doesn't make strength training less useful. It has its own benefits for muscle and bone, which we cover in exercise and longevity. It just didn't move this particular marker in this study.
Does diet affect telomere length?
Diet is linked to telomere length in observational studies, which can't prove cause and effect. In the Nurses' Health Study, 4,676 women whose eating pattern was closest to a Mediterranean diet had longer blood telomeres than those whose diets were furthest from it, after adjusting for other factors (Crous-Bou et al., 2014). Our guide to the Mediterranean diet explains what that pattern looks like day to day.
Studies linking individual vitamins or supplements to telomere length are mostly observational too. None of the sources in this guide shows a supplement lengthening telomeres in people.
Does stress shorten telomeres?
Long-term psychological stress has been linked to shorter telomeres. In a 2004 study of healthy women, those reporting the highest stress had telomeres shorter by the equivalent of at least a decade of extra aging compared with the lowest-stress women. Higher stress also went with lower telomerase activity (Epel et al., 2004).
That study was cross-sectional, so it shows an association at one point in time. Still, it's one reason stress, sleep and recovery show up alongside diet and exercise in healthy aging research. See our guides to sleep and aging and nutrition and stress.
What can you realistically do about your telomeres?
You can't measure or steer your telomeres precisely, but the habits linked to longer telomeres are the same ones with strong evidence for healthy aging overall:
- Regular endurance exercise: running or interval training three times a week was the strongest result in a randomized trial.
- A Mediterranean-style diet: vegetables, legumes, whole grains, fish and olive oil.
- Managing long-term stress.
OPA Nutrition doesn't sell a telomere supplement, and this guide doesn't recommend one. For how telomeres fit with the other hallmarks of aging, see healthspan vs lifespan.
Frequently Asked Questions
What are telomeres in simple terms?
Telomeres are protective caps of repeated DNA on the ends of chromosomes, a bit like the plastic tips on shoelaces. They shorten as cells divide.
How do you increase telomere length?
No method reliably lengthens telomeres in people. In one 6-month trial, endurance and interval training increased telomerase activity and telomere length in blood cells.
What is telomerase?
Telomerase is an enzyme that rebuilds telomeres by adding DNA repeats to chromosome ends. Most adult cells make too little of it to stop telomeres from shortening with age.
Can you check your telomere length?
Yes, some labs and consumer kits measure telomere length, usually in blood cells. Results vary by method and between people of the same age, so a single result says little about your own health.
What vitamin lengthens telomeres?
None has been shown to lengthen telomeres in people. Links between vitamins and telomere length come mostly from observational studies.
Can telomeres grow back?
Telomerase can add DNA repeats back onto telomeres. In a 6-month exercise trial, average telomere length in several types of blood cells increased in the endurance and interval training groups.
Sources
- Srinivas N, Rachakonda S, Kumar R. Telomeres and telomere length: a general overview. Cancers (Basel). 2020;12(3):558. PubMed 32121056
- The Nobel Assembly at Karolinska Institutet. The Nobel Prize in Physiology or Medicine 2009, press release. nobelprize.org
- Harley CB, Futcher AB, Greider CW. Telomeres shorten during ageing of human fibroblasts. Nature. 1990;345(6274):458-460. PubMed 2342578
- Cawthon RM, Smith KR, O'Brien E, Sivatchenko A, Kerber RA. Association between telomere length in blood and mortality in people aged 60 years or older. Lancet. 2003;361(9355):393-395. PubMed 12573379
- Sanders JL, Newman AB. Telomere length in epidemiology: a biomarker of aging, age-related disease, both, or neither? Epidemiol Rev. 2013;35(1):112-131. PubMed 23302541
- Telomeres Mendelian Randomization Collaboration; Haycock PC, Burgess S, Nounu A, et al. Association between telomere length and risk of cancer and non-neoplastic diseases: a Mendelian randomization study. JAMA Oncol. 2017;3(5):636-651. PubMed 28241208
- Werner CM, Hecksteden A, Morsch A, et al. Differential effects of endurance, interval, and resistance training on telomerase activity and telomere length in a randomized, controlled study. Eur Heart J. 2019;40(1):34-46. PubMed 30496493
- Crous-Bou M, Fung TT, Prescott J, et al. Mediterranean diet and telomere length in Nurses' Health Study: population based cohort study. BMJ. 2014;349:g6674. PubMed 25467028
- Epel ES, Blackburn EH, Lin J, et al. Accelerated telomere shortening in response to life stress. Proc Natl Acad Sci U S A. 2004;101(49):17312-17315. PubMed 15574496
- Images: Pavel Danilyuk (featured image), Katarzyna Modrzejewska and Rendi iD, via Pexels (free Pexels license).
Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.
