Why the path to human longevity runs through dogs

Laboratory aging research has produced interventions that extend the lifespan of mice, and the field's stated barrier is moving those results to people[1]. In people, the first proposed trial of a drug against aging, TAME, tests metformin as an initial step toward later drugs[5], and the life-table arithmetic below shows why no human trial has read out a lifespan effect. Companion dogs are the one species in which a lifespan trial of a drug against aging is being run outside the laboratory[7], in the human environment, with a regulator that has accepted lifespan extension as something a drug can be approved for[18]. The numbers below are computed from the cited sources so that the comparison can be checked rather than believed.

The clock problem

A lifespan intervention has to be judged on deaths. In mice that takes a year or two: the Interventions Testing Program's rapamycin result came from feeding genetically heterogeneous mice from 600 days of age and reading the age at which 90% had died, a 14% gain for females and 9% for males[2]. In rhesus monkeys the calorie-restriction answer took a 20-year longitudinal study[3][4]. In people, using the United States 2019 life table, half of a cohort enrolled at 65 is still alive 21 years later[9]. In companion dogs, using the UK life table built from 30,563 deaths, half of a cohort enrolled at 8 has died after 4.6 years[8]. A dog trial started this year has its lifespan answer within a single five-year grant period[16].

Years from the first dose to a lifespan answer Mice (ITP, rapamycin from 600 days) last deaths about a year and a half after a start at 600 days Dogs (from age 8) 4.6 years until half the dogs have died Rhesus monkeys (calorie restriction) 20-year longitudinal study People (from age 65) 21 years until half the people have died Sources: Harrison 2009; Teng 2022 (UK dog life table); Colman 2009; WHO life tables, USA 2019. CC BY 4.0, w0lph.github.io/k9/why-dogs.html
Years from the first dose to a lifespan answer, by species. SVG, CC BY 4.0.

What dogs share with us that mice do not

Companion dogs live in our homes, eat our food, breathe our air and have a sophisticated healthcare system of their own, and they develop the same age-related diseases, which is the rationale of the Dog Aging Project[6] and of the first rigorous test of a drug against biological aging with lifespan endpoints to be run outside a laboratory in any species[7]. The domestic dog is among the most variable mammals in size, disease risk and life expectancy[6]: breeds span almost two orders of magnitude in body size and a twofold range in life expectancy, and the large breeds die young mainly because they age faster[10]. That is a natural experiment on growth and aging that no inbred laboratory strain offers.

Lifespan has already been moved in dogs

Restricting food intake by 25% from eight weeks of age gave 48 Labrador Retrievers a median lifespan 1.8 years longer and delayed chronic disease[11][12]. L-deprenyl started between 10 and 15 years of age lengthened survival in beagles[13]. Rapamycin, the mouse result replicated at the ITP's three sites[2], was well tolerated in two placebo-controlled trials in middle-aged companion dogs[14][15], and TRIAD, a randomized, double-masked, placebo-controlled, multicenter trial with lifespan and healthspan endpoints, is funded from December 2024 to November 2029[7][16].

A regulator has already said yes

The FDA Center for Veterinary Medicine's expanded conditional approval pathway allows a drug with a reasonable expectation of effectiveness to reach the market while the pivotal study completes[17]. In 2023 it accepted that a drug intended to extend lifespan in large dogs has a reasonable expectation of effectiveness, the first such acceptance for any species[18]; in January 2026 it accepted the target-animal-safety section for a daily pill intended to extend healthy lifespan in senior dogs[19], whose pivotal study follows 1,300 dogs at 70 veterinary practices for up to four years[20]. There is no equivalent indication for people. If that pipeline holds, the first approved longevity drug in any species will be a dog drug, and its effectiveness data will be the first lifespan-trial data in a mammal that lives with us.

Dog results read across

Epigenetic clocks built on the same methylation array estimate age in both dogs and humans, including dual-species clocks, so an intervention's effect on biological age can be measured with one instrument in both species[21]. Doses translate by body-surface area with the published conversion factors[23]. The registry of trials, the FDA summaries and the literature on this site exist so that a result in dogs can be carried into a human protocol with its sources attached.

Run the comparison yourself

Pick a compound the Interventions Testing Program has tested in mice. The calculator shows the mouse results from DrugAge, what is known in dogs from this site's database, the dog-equivalent dose, and the trial it would take to detect the same lifespan extension in dogs starting at 8 and in people starting at 65, over the same follow-up. Of the 54 ITP compounds, 20 are mentioned anywhere in the canine aging literature and 0 have a dog lifespan study.

Model: a p% lifespan extension starting at age a delays mortality by a·p/(1+p) years; under Gompertz mortality fitted to each life table (dogs, ages 7-13[8]; people, ages 60-84[9]) that delay is a constant hazard ratio; events needed follow Schoenfeld's formula at two-sided α = 0.05 and 80% power[22]; participants are events divided by the control arm's cumulative mortality over the follow-up, with 1:1 allocation. With these defaults a 10% extension needs about 1,377 dogs over four years and about 2,131 people over the same four years, and the people are then still 17 years short of a median-lifespan readout. Change the inputs; the arithmetic is in the page source.

Forecast it

Five play-money prediction markets put the same comparison to forecasters, in pairs: a dog question next to its human twin. Trade them on Manifold and the crowd's numbers appear here over time.

References

  1. Kaeberlein M, Creevy KE, Promislow DEL. The dog aging project: translational geroscience in companion animals. Mammalian Genome 2016. https://doi.org/10.1007/s00335-016-9638-7
  2. Harrison DE et al. Rapamycin fed late in life extends lifespan in genetically heterogeneous mice. Nature 2009. https://doi.org/10.1038/nature08221
  3. Colman RJ et al. Caloric restriction delays disease onset and mortality in rhesus monkeys. Science 2009. https://doi.org/10.1126/science.1173635
  4. Mattison JA et al. Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study. Nature 2012. https://doi.org/10.1038/nature11432
  5. Barzilai N, Crandall JP, Kritchevsky SB, Espeland MA. Metformin as a tool to target aging. Cell Metabolism 2016. https://doi.org/10.1016/j.cmet.2016.05.011
  6. Creevy KE et al. An open science study of ageing in companion dogs. Nature 2022. https://doi.org/10.1038/s41586-021-04282-9
  7. Test of Rapamycin in Aging Dogs (TRIAD): study design and rationale. GeroScience 2025. https://doi.org/10.1007/s11357-024-01484-7
  8. Teng KT et al. Life tables of annual life expectancy and mortality for companion dogs in the United Kingdom. Scientific Reports 2022. https://doi.org/10.1038/s41598-022-10341-6
  9. WHO Global Health Observatory. Life tables by country: probability of dying between age x and x+n, United States, 2019. https://www.who.int/data/gho/data/indicators/indicator-details/GHO/gho-ghe-life-tables-by-country
  10. Kraus C, Pavard S, Promislow DEL. The size-life span trade-off decomposed: why large dogs die young. The American Naturalist 2013. https://doi.org/10.1086/669665
  11. Kealy RD et al. Effects of diet restriction on life span and age-related changes in dogs. JAVMA 2002. https://doi.org/10.2460/javma.2002.220.1315
  12. Lawler DF et al. Diet restriction and ageing in the dog: major observations over two decades. British Journal of Nutrition 2008. https://doi.org/10.1017/S0007114507871686
  13. Ruehl WW et al. Treatment with L-deprenyl prolongs life in elderly dogs. Life Sciences 1997. https://doi.org/10.1016/s0024-3205(97)00611-5
  14. Urfer SR et al. A randomized controlled trial to establish effects of short-term rapamycin treatment in 24 middle-aged companion dogs. GeroScience 2017. https://doi.org/10.1007/s11357-017-9972-z
  15. A masked, placebo-controlled, randomized clinical trial evaluating safety and the effect on cardiac function of low-dose rapamycin in 17 healthy client-owned dogs. Frontiers in Veterinary Science 2023. https://doi.org/10.3389/fvets.2023.1168711
  16. NIH RePORTER. R01AG090843, Test of Rapamycin in Aging Dogs, Texas A&M AgriLife Research, project period 2024-12-01 to 2029-11-30. https://reporter.nih.gov/project-details/11027111
  17. FDA Center for Veterinary Medicine. GFI #261: Eligibility criteria for expanded conditional approval of new animal drugs (2021). https://www.fda.gov/regulatory-information/search-fda-guidance-documents/cvm-gfi-261-eligibility-criteria-expanded-conditional-approval-new-animal-drugs
  18. dvm360. FDA determines drug for lifespan extension in large dogs to have a reasonable expectation of effectiveness (2023). https://dvm360.com/view/fda-determines-drug-for-lifespan-extension-in-large-dogs-to-have-a-reasonable-expectation-of-effectiveness
  19. Loyal. FDA accepts the Target Animal Safety technical section for LOY-002 (13 January 2026). https://loyal.com/posts/loy-002-tas
  20. Loyal. The STAY study: 1,300 dogs at 70 veterinary practices, up to four years. https://loyal.com/stay
  21. Horvath S et al. DNA methylation clocks for dogs and humans. PNAS 2022. https://doi.org/10.1073/pnas.2120887119
  22. Schoenfeld DA. Sample-size formula for the proportional-hazards regression model. Biometrics 1983. https://doi.org/10.2307/2531021
  23. FDA Center for Drug Evaluation and Research. Estimating the maximum safe starting dose in initial clinical trials (2005): body-surface-area conversion factors (Km). https://www.fda.gov/regulatory-information/search-fda-guidance-documents/estimating-maximum-safe-starting-dose-initial-clinical-trials-therapeutics-adult-healthy-volunteers