Telomeres and Longevity: What They Actually Tell Us - and What They Do Not
Telomeres - the protective caps at the ends of chromosomes - are among the most popularized aging biomarkers in the public consciousness. Telomere length testing has been marketed as a direct window into your biological age and remaining lifespan. The reality is more nuanced than the popular narrative suggests.
- Telomeres are arrays of TTAGGG repeats at chromosome ends, protected by a six-protein complex called shelterin that stops cells mistaking them for damaged DNA.2
- Telomeres shorten with age in dividing tissues, fastest early in life, and short telomeres are associated with higher rates of disease and death.4
- Across 121,749 people, each standard deviation shorter blood telomere length was linked to only 9% higher mortality, with results varying by measurement technique and age.1
- Longer is not simply better: in a genetic study, longer telomeres were linked to lower coronary heart disease risk but higher risk of several cancers.7
- Telomerase, the enzyme that rebuilds telomeres, is repressed in normal body tissues but active in about 90% of tumour biopsies, one reason telomerase-activating supplements call for caution.6
Telomere biology earned Elizabeth Blackburn, Carol Greider and Jack Szostak the 2009 Nobel Prize in Physiology or Medicine. Telomere length testing has since been marketed to consumers, but the link between blood telomere length and survival is modest: in a 2018 meta-analysis of 25 studies with 121,749 people and 21,763 deaths, each standard deviation shorter telomere length was linked to 9% higher mortality, and people in the shortest quarter had 26% higher mortality than those in the longest.1
Telomere Biology: The Basics
Human telomeres are arrays of TTAGGG repeats added by telomerase. Six telomere-specific proteins, together called shelterin, bind them and let cells tell chromosome ends apart from sites of DNA damage; without shelterin, chromosome ends are processed inappropriately by DNA repair pathways.2 Telomeres shorten with age in dividing tissues, fastest early in life, and short telomeres are thought to limit further cell division.4
Telomerase: The Enzyme That Rebuilds Telomeres
Telomerase, the enzyme that adds telomere repeats, was first identified in 1985 in the single-celled organism Tetrahymena.3 In humans it is stringently repressed in most normal body tissues but reactivated in cancer: a 1994 study found telomerase activity in 98 of 100 immortal cell populations and in 90 of 101 tumour biopsies, but in none of 50 normal tissue samples.6 That is why activating telomerase is treated with caution.
What Telomere Length Testing Actually Tells You
Consumer tests usually measure average telomere length in white blood cells. In the 2018 meta-analysis, measurement technique and age at measurement contributed to differences between studies, and the link with mortality was weaker in people over 80.1 A 2017 Mendelian randomization study, which uses genetic variants to estimate cause and effect, found that genetically longer telomeres were associated with lower coronary heart disease risk (odds ratio 0.78 per standard deviation) but higher risk of several cancers, including glioma, lung adenocarcinoma and melanoma.7 So a longer result is not simply better.
Can Lifestyle Change Telomeres?
Evidence that lifestyle changes lengthen telomeres is limited. In one often-cited study, 10 men with low-risk prostate cancer who made comprehensive changes to diet, activity, stress management and social support had a small increase in relative telomere length over five years, while 25 comparison men who were not randomized had a small decrease; greater adherence was associated with longer telomeres.5 A study this small and unrandomized cannot show that the changes caused the difference.
The bottom line: a single telomere test says little about an individual's future. Habits such as exercise, sleep, a healthy diet and not smoking are worth building for their proven benefits, whatever your telomere result.
Put this research into practice: Biological Age Calculator
References
- 1Wang Q, et al. "Telomere Length and All-Cause Mortality: A Meta-analysis." Ageing Res Rev. 2018;48:11-20. PubMed · DOI
- 2de Lange T. "Shelterin: the protein complex that shapes and safeguards human telomeres." Genes Dev. 2005;19(18):2100-10. PubMed · DOI
- 3Greider CW, Blackburn EH. "Identification of a specific telomere terminal transferase activity in Tetrahymena extracts." Cell. 1985;43(2 Pt 1):405-13. PubMed · DOI
- 4Eisenberg DT. "An evolutionary review of human telomere biology: the thrifty telomere hypothesis and notes on potential adaptive paternal effects." Am J Hum Biol. 2011;23(2):149-67. PubMed · DOI
- 5Ornish D, et al. "Effect of comprehensive lifestyle changes on telomerase activity and telomere length in men with biopsy-proven low-risk prostate cancer: 5-year follow-up of a descriptive pilot study." Lancet Oncol. 2013;14(11):1112-1120. PubMed · DOI
- 6Kim NW, et al. "Specific association of human telomerase activity with immortal cells and cancer." Science. 1994;266(5193):2011-5. PubMed · DOI
- 7Haycock PC, 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 · DOI
