Your chronological age is fixed, but your biological age is not. One of the most studied markers of that difference is telomere length.
Telomeres are the protective caps at the ends of your chromosomes. They shorten a little each time a cell divides.
A 2025 study in PLOS One of 368 Korean adults, ages 23 to 90, found that everyday habits track closely with how old cells look at the DNA level. The authors reported that regular exercise slowed telomere aging in both sexes, while chronic stress accelerated it.
What the Korean data showed
The researchers measured telomere length in blood and compared it with survey data on lifestyle. Five factors kept surfacing. Smoking, alcohol intake, chronic stress, sleep duration, and physical activity all showed independent links to biological aging.
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Sleep in the range of seven to eight hours a night was tied to slower telomere shortening. Smoking pack-years and heavier alcohol use pushed in the opposite direction. The authors concluded that the results "emphasize the importance of lifestyle in the management of biological aging."
The genetic evidence points the same way
Observational studies like the Korean one can be blurred by confounders. A large Mendelian randomization study of 472,174 UK Biobank participants, published in Journal of Translational Medicine in 2024, used inherited genetic variants to test whether the links were likely to be causal.
Genetic liability to lifetime smoking was "robustly associated with shorter telomere length" in that analysis, and genetically predicted insomnia was linked to shorter telomeres as well. Moderate-to-vigorous physical activity showed a suggestive association with longer telomeres. The smoking and insomnia signals held up after adjusting for body mass index, type 2 diabetes, and alcohol use.
Men and women were not affected the same way
The Korean data suggested the five habits do not weigh equally by sex. In men, exercise, smoking, and chronic stress emerged as the significant contributors to telomere aging. In women, exercise, alcohol consumption, sleep, and stress mattered most.
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Exercise and chronic stress showed up strongly on both lists, which fits a broader pattern in the aging literature that movement and stress load act on cells across the population.
Can lifestyle change push telomeres back?
The most cited evidence for partial reversal comes from a small pilot study led by Dean Ornish, published in The Lancet Oncology in 2013. Ten men with low-risk prostate cancer who adopted a program of a plant-based diet, moderate exercise, stress management, and social support saw mean telomere length rise from 0.63 to 0.69 T/S units over five years, while a comparison group of 25 men on active surveillance alone saw their telomeres drift down.
The bigger the lifestyle change, the larger the effect. The study was small and enrolled a specific patient group, so its numbers should not be read as a guarantee of reversal in the general population.
What a telomere reading can and cannot tell you
Telomere length is one of the best-studied biomarkers of biological aging, and shorter telomeres have been linked in meta-analyses to higher risks of cardiovascular disease, type 2 diabetes, and cognitive decline. It is not, however, a single definitive test for how old the body is. Researchers now recommend reading telomere length alongside other markers, such as epigenetic clocks, rather than in isolation.
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The practical takeaway is unglamorous. Not smoking, moderating alcohol, sleeping seven to eight hours, moving regularly, and finding realistic ways to handle stress are the same habits that already protect the heart and brain. The telomere research adds one more reason to take them seriously, and hints that starting later is better than not starting at all.
If you are trying to change any of these habits and have an underlying condition or take regular medication, talk with your doctor before making big shifts, especially around exercise intensity or alcohol cessation.
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