Your fitness may say less about cellular aging than you think

By Dr. Chinta SidharthanReviewed by Susha Cheriyedath, M.Sc.Nov 12 2026

Can your physical fitness reveal how quickly your cells are aging? Researchers compared exercise performance, lifestyle habits, psychological stress, and chronic disease in middle-aged adults to investigate what telomere length really tells us about aging.

Study: Midlife telomere length is associated with perceived stress and chronic disease rather than lifestyle or physical function. Image Credit: Sashkin / Shutterstock

Telomeres, the protective caps on chromosomes, generally shorten with advancing age, and this gradual wearing down is a key marker of cellular aging. In a recent cross-sectional study published in the journal Scientific Reports, researchers tested whether fitness, lifestyle, stress, and chronic disease were associated with telomere length. The research was conducted by scientists from Vilnius University, Vytautas Magnus University, Kaunas University of Technology, and the Lithuanian University of Health Sciences in Lithuania.

Telomere shortening

As telomeres shorten, they can become less effective at protecting chromosomes. Critically short telomeres can push cells into a state where they stop dividing, and telomere length is often treated as a marker of biological aging.

Scientists have linked shorter telomeres to poor sleep, chronic stress, obesity, and several age-related diseases, while physical activity is thought to offer modest protection. Yet links between telomere length and fitness or lifestyle tend to be weak and inconsistent, and it remains unclear whether telomere length in midlife reflects how well the body currently functions or the stress accumulated over many years.

The current study

In this study, the researchers recruited 84 adults from a general-population cohort in Lithuania, most of whom were middle-aged, with an average age of 51 years. All participants provided informed consent.

They obtained blood samples from all participants, and telomere length in white blood cells was measured at a clinical laboratory in Madrid, Spain, using high-throughput quantitative fluorescence in situ hybridization (HT Q-FISH), a method in which fluorescent probes attach to telomeres so their length can be estimated from the signal. The laboratory reported the median telomere length, the average telomere length, and the length below which the shortest 20% of telomeres fell. A telomere-based estimate of biological age, calculated using a proprietary laboratory algorithm, was also provided.

The researchers then assessed body composition using bioelectrical impedance analysis, along with body mass index and waist-to-hip ratio. Cardiometabolic health was also recorded through blood pressure, glucose, albumin, triglycerides, and cholesterol.

Participants also underwent several physical fitness assessments, which covered handgrip strength, knee extension strength on an isokinetic dynamometer, jump performance on force plates, and a graded treadmill test that recorded peak oxygen uptake and the respiratory quotient (RQ), which compares carbon dioxide output with oxygen uptake during exercise. Reaction time and hand dexterity were also measured to assess neuromotor function.

The participants completed questionnaires on weekly moderate-to-vigorous physical activity, estimated daily steps, sedentary time, smoking, alcohol intake, and monthly sauna visits. Sleep habits were assessed with selected items from the Pittsburgh Sleep Quality Index, and perceived stress was rated with the 10-item Perceived Stress Scale, which asks about experiences during the previous month.

For the analysis, the team applied linear regression models adjusted for age and sex. These initial analyses examined each factor separately. Two multivariable models then tested physiological factors and demographic and psychosocial factors separately.

Major findings

The researchers reported that telomere length in midlife showed different association patterns across the initial analyses and the two multivariable models.

Of the 84 participants, 64% were men, 72.6% were obese or overweight, and 28.6% reported a chronic disease. The median telomere length was about 9.6 kilobases, and a proprietary telomere-based calculation estimated biological age to be, on average, 4.6 years above chronological age, with wide variation between individuals.

After adjusting for age and sex, no measure of body composition, blood chemistry, muscle strength, aerobic fitness, reaction time, physical activity, sleep, or sauna use was significantly linked to telomere length. Perceived stress, waist-to-hip ratio, and RQ during exercise showed suggestive trends with telomere measures, but none reached statistical significance, including after correction for multiple comparisons.

Initial assessment of physiological factors revealed that older age and a greater waist-to-hip ratio, which is a marker of abdominal fat, were linked to shorter median telomeres, while only age was tied to the shortest 20% of telomeres. After additional statistical checks, only the link between age and median telomere length held.

The model assessing demographic and psychosocial factors included age, sex, perceived stress, and chronic disease. Higher perceived stress and older age were each independently associated with shorter median telomere length and a lower 20th-percentile telomere length, and both associations remained significant after the same statistical adjustment.

The authors also interpreted chronic disease status as associated with shorter telomeres, but the disease-status coding in their results table appears inconsistent with that interpretation and needs clarification. Sex showed no association. This model accounted for about one fifth of the variation in telomere length, slightly more than the physiological model, leaving most of the variation unexplained.

In practical terms, the findings suggest that current physical capacity and cellular aging markers do not necessarily follow the same pattern during midlife. The study measured recent perceived stress rather than stress accumulated over a lifetime. However, the authors noted that the cross-sectional design cannot establish cause and effect, and the sample was small and generally healthy, making it difficult to generalize the results to older or more medically diverse populations. Since lifestyle habits were assessed at a single point in time, the analysis might have missed the effects of behaviors maintained over decades. The lack of an observed link with current activity does not rule out benefits from lifelong exercise.

Conclusions

Among these middle-aged adults, current fitness and lifestyle habits showed no consistent independent associations with telomere length, suggesting that cellular and functional aging may not always progress together.

The findings suggested that telomere length should be interpreted as one indicator of cellular aging, but a single blood-based measure cannot capture all aspects of biological aging. These findings call for larger, longitudinal studies that track people over many years to test whether these patterns hold.