# Healthspan versus lifespan: what these studies actually measured > Healthspan versus lifespan: what these studies actually measured — yolopeptide — The organising question behind these Longevity & Cellular Health research peptides: which endpoints the epitalon and MOTS-c literature actually measures — survival curves, functional capacity, clinical associations, cell-culture surrogates — and what each can and cannot settle. **THE ORGANISING QUESTION** Twelve studies, four kinds of endpoint, and one distinction that decides how nearly every longevity claim should be read. ## The short version A longevity claim is only as good as the thing the study counted. There are four kinds of counting in this literature, and they are not interchangeable. Some studies count deaths, and produce a survival curve — the only measurement that is directly about lifespan. Some count what an ageing animal can still do: how far it runs, how hard it grips. That is a measurement of function, which is what healthspan means. Some watch a group of people over years and note who does better, without ever assigning anyone to a treatment. And some measure something inside a cell in a dish — the length of a chromosome cap, the level of an enzyme — and treat it as a stand-in for both. The fourth kind is the most common and the least conclusive, and it is the kind most often quoted in advertising. This page sorts the twelve studies behind this desk into those four categories and states what each can and cannot settle. ## Four kinds of endpoint | Endpoint type | What it counts | In this literature | What it can settle | | --- | --- | --- | --- | | Survival curve | Deaths over time in a defined cohort | Epitalon in female SHR mice [11] | Lifespan, in that species and strain | | Functional capacity | What an ageing animal can still do | MOTS-c and treadmill capacity, grip strength, gait [4]; muscle atrophy and glucose uptake [1] | Healthspan-shaped function, in animals | | Clinical-outcome association | Who fares better, without assignment | Epithalamin in 266 elderly people [10]; circulating MOTS-c in 94 dialysis patients [2] | Correlation only; no causal claim | | Cellular surrogate | A mechanism marker in cells | Telomerase and telomere length [9][7]; melatonin enzymes [8]; oocyte reactive oxygen species and mitochondria [12]; nuclear gene programmes [5] | Plausibility of a mechanism | Read down the right-hand column and the shape of the field becomes clear. Exactly one row can speak to lifespan, and it is a mouse row. Exactly one row can speak to function, and it is also an animal row. Both human rows are associations. Everything else is mechanism. ## What a survival curve does and does not say The single survival result here is worth reading carefully, because it is more informative than its own headline. Epitalon in female SHR mice increased maximum lifespan 12.3% and survival of the last 10% of the cohort 13.3%, while mean lifespan was unchanged [11]. Maximum lifespan and mean lifespan answer different questions. Mean lifespan moves when a treatment helps typical animals — usually by reducing the ordinary causes of mid-life death. Maximum lifespan moves when something changes at the far tail of the curve, among the animals that were already going to be long-lived. A result in the tail without a result in the middle is a real finding and a narrow one, and it does not support a claim that lives are generally longer. The same study's other numbers point somewhere else again. Chromosome aberrations in bone marrow fell 17.1% and leukaemia was inhibited 6.0-fold, while total tumour incidence was unchanged [11]. Fewer of one disease, not less disease. That is a compositional shift, and calling it "anti-ageing" flattens the detail that makes it interesting. ## The surrogate problem, and why telomere claims are overstated Telomere length is the most quoted surrogate in consumer longevity writing, and the reasoning behind the quoting is usually left implicit: telomeres shorten with cell division, short telomeres accompany cellular senescence, therefore lengthening telomeres reverses ageing. Each step of that chain is weaker than the sentence implies. What the epitalon studies established is narrower and quite specific. In telomerase-negative human fetal fibroblasts, the peptide induced the catalytic telomerase subunit, telomerase activity, and telomere elongation [9]. In 2025 that was repeated across human cell lines at 0.1 to 1 microgram per millilitre, with dose-dependent lengthening through hTERT in normal cells [7]. Both are results about cells growing in a dish under laboratory conditions. Neither measures telomere length in a living person, and no study on this desk does. The 2025 replication also complicates the story it confirms. In breast-cancer cell lines, telomere extension proceeded largely through Alternative Lengthening of Telomeres rather than the hTERT route, and that ALT signal was significant in cancer lines while remaining minor in normal ones [7]. Telomerase reactivation is a hallmark of most cancers, so a compound that reaches these pathways is not straightforwardly a rejuvenation agent; the long-term oncological implications in humans are unresolved. That is a genuine open question, not a disclaimer added for form. ## The mitochondrial claim, read the same way "Mitochondrial-derived" is doing heavy marketing work wherever MOTS-c is sold, because it suggests the peptide repairs or rejuvenates mitochondria. The measured mechanism is a different kind of thing: MOTS-c inhibits the folate cycle and de novo purine synthesis, raising AICAR and activating AMPK, and under stress it translocates to the nucleus and regulates antioxidant and metabolic gene programmes in an AMPK-dependent way [5]. A 2024 study added direct binding to and activation of casein kinase 2 [1]. That is a signalling story — the mitochondrion telling the rest of the cell something — not a repair story. The functional data are the strongest part of the file and they are honest about their species: treadmill capacity, grip strength and gait improved in mice aged 22 to 23.5 months, with exercise shown to induce the endogenous peptide in the same work [4]. The human data are of a different type entirely. Circulating MOTS-c was independently associated with a mortality and cardiovascular composite in 94 haemodialysis patients, improving model discrimination from an ROC area under the curve of 0.727 to 0.743 [2]. An association between a person's own peptide level and their outcome is compatible with the peptide being protective, and equally compatible with it being a readout of how healthy their mitochondria already are. ## What is missing from the table The absences are as informative as the entries, and they are the same absences for both compounds. There is no randomised, placebo-controlled human trial of either peptide. There is no published human pharmacokinetic study for either, meaning no measured half-life, bioavailability or dose-response — which is why no schedule appears anywhere on this site. There is no human study of any duration measuring a healthspan endpoint: nothing counting years lived without disability, physical capacity in older adults, or time to functional decline. And there is no survival result of any kind for MOTS-c. That leaves the field in a specific and unglamorous position. One mouse survival curve with a narrow shape, one mouse functional dataset, two human association studies, a set of cell-culture mechanisms, and a marketplace that speaks with far more confidence than any of it warrants. The distinction between healthspan and lifespan is not a philosophical nicety here. It is the tool that keeps that gap visible. --- A reference desk for the ageing-and-cellular-health literature: every figure here traces to a listed study, and none of it is a clinic, a vendor, or a protocol.