Dog Years is to Human Years as 7 is to 1 = Wrong

The 7 dog years to 1 human year fallacy was empirically corrected when a research team published their 2017 Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome study in the journal Cell Systems, laying out new methodology using DNA Methylome to create an epigenetic aging clock for dogs and wolves in relation to a human year.

Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome | Cell Systems

I love how the above illustration points out that at human year 1, dogs are roughly 31-32 years old, so we're talking Tom Hanks in Splash (1984), The Man with One Red Shoe (1985) and Big (1988). Also of note in the above illustration, at around 4 human years, a dog is roughly Tom Hanks ala Charlie Wilson's War (2007), and at 9 human years is everything that comes afterwards; that's Angels & Daemons (2009), Toy Story 3 (2010), Cloud Atlas (2012), Captain Phillips (2013), Bridge of Spies (2015), Sully (2016), Toy Story 4 (2019), A Beautiful Day In The Neighborhood (2019), Greyhound (2020), News of The World (2020), Finch (2021), Pinocchio (2022), A Man Called Otto (2022), some unnamed movies and everything to come till 2024; all of that and a bag of chips can be captured in 5 human years from 4 to 9.

All mammals progress through similar physiological stages throughout life, from early development to puberty, aging, and death. Yet, the extent to which this conserved physiology reflects underlying genomic events is unclear. Here, we map the common methylation changes experienced by mammalian genomes as they age, focusing on comparison of humans with dogs, an emerging model of aging. Using oligo-capture sequencing, we characterize methylomes of 104 Labrador retrievers spanning a 16-year age range, achieving >150× coverage within mammalian syntenic blocks. Comparison with human methylomes reveals a nonlinear relationship that translates dog-to-human years and aligns the timing of major physiological milestones between the two species, with extension to mice. Conserved changes center on developmental gene networks, which are sufficient to translate age and the effects of anti-aging interventions across multiple mammals. These results establish methylation not only as a diagnostic age readout but also as a cross-species translator of physiological aging milestones.

Quantitative Translation of Dog-to-Human Aging by Conserved Remodeling of the DNA Methylome | NIH

In May, 2022, a team of researchers expanded the realm of known science to encompass data gathered across 93 domestic dog breeds using Tina Wang's published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS) DNA methylation clocks for dogs and humans:

DNA methylation profiles have been used to develop biomarkers of aging known as epigenetic clocks, which predict chronological age with remarkable accuracy and show promise for inferring health status as an indicator of biological age. Epigenetic clocks were first built to monitor human aging, but their underlying principles appear to be evolutionarily conserved, as they have now been successfully developed for many mammalian species. Here, we describe reliable and highly accurate epigenetic clocks shown to apply to 93 domestic dog breeds. The methylation profiles were generated using the mammalian methylation array, which utilizes DNA sequences that are conserved across all mammalian species. Canine epigenetic clocks were constructed to estimate age and also average time to death. We also present two highly accurate human–dog dual species epigenetic clocks (R=0.97), which may facilitate the ready translation from canine to human use(or vice versa) of antiaging treatments being developed for longevity and preventive medicine. Finally, epigenome-wide association studies here reveal individual methylation sites that may underlie the inverse relationship between breed weight and lifespan. Overall, we describe robust biomarkers to measure aging and, potentially, health status in canines.

Ideally, model species for antiaging research should be representative of human characteristics such as size and genetic diversity, as well as shared environment. Domestic dogs (Canis lupus familiaris) fulfill most of these criteria, offering a unique opportunity to evaluate the effectiveness of emerging antiaging interventions (1–5). There is also a significant need to develop health-monitoring tools for dogs, as there are more than 76million companion dogs in the United States alone (6).

Over 340 dog breeds are recognized worldwide, which are each a closed breeding population under strong selection for morphologic and behavioral traits. As a result, dogs share extensive phenotypic and genetic homogeneity within breeds and increased heterogeneity between breeds (7). Small breeds live considerably longer than large breeds (8), offering the rare chance to understand the relationship between size and lifespan within a single mammalian species. Dogs also share a similar yet accelerated trajectory of development as humans including infancy, puberty, adulthood, and senescence in about 20% of the human lifespan (5, 9). As a result, dogs represent an ideal system for studies of comparative aging, where intrabreed studies can be conducted on a background of limited diversity.

Our previous work on DNA-methylation-based age estimators (i.e., epigenetic clocks)for dogs and wolves (10) described one of the first nonhuman epigenetic clocks. We deter-mined that the age dependence of DNA methylation (DNAm) is conserved at syntenic sites in the genomes of multiple mammalian species including humans. However, a small sample size (n<150) and technical limitations associated with the measurement platform(reduced representation bisulfite sequencing) limited the generalizability of the results. Furthermore, our initial study utilized only a few canine breeds, which prevented testing the relationship between epigenetic aging and breed lifespan. Here, we report the development of a canine epigenetic clock based on 93 recognized dog breeds (11) using a mammalian array (HorvathMammalMethylChip40) that profiles highly conserved cytosines across mammalian species (12).In this study, we present dual-species epigenetic clocks that apply to both humans and dogs. We test whether short-lived breeds exhibit faster epigenetic aging than long-lived breeds and develop epigenetic predictors of the average time to death. Finally, we investigate the relation-ship between breed size and lifespan and characterize 5'-C-phosphate-G-3' regions (CpGs) that are correlated with age or breed characteristics such as median lifespan or average adult weight.

DNA methylation clocks for dogs and humans | PNAS

The ultimate answer about your particular dog is "depends". Depends on the weight of your dog, and it's relative size and genetic degradation rate vs what's "normal", which to be fair is still just a setting on the washer/dryer to me. Looking at a 9 month old dog having babies correlating to roughly 23 years old'ish instead of 5 and a quarter years old'ish makes sense:

What emerged from the study is a graph that can be used to match up the age of your dog with the comparable human age (see figure). The comparison is not a 1:7 ratio over time. Especially when dogs are young, they age rapidly compared to humans. A one-year-old dog is similar to a 30-year-old human. A four-year-old dog is similar to a 52-year-old human. Then by seven years old, dog aging slows.

"This makes sense when you think about it — after all, a nine-month-old dog can have puppies, so we already knew that the 1:7 ratio wasn't an accurate measure of age," Ideker said.

How dogs actually age (and what that tells us about how we do) | University of California

This research has the ability to create an efficacy metric for anti-aging products, procedures, regimens and whatever new nouns the future spawns around looking and feeling young, by observing the tiny additions and deletions at the genetic level juxtaposed against the fine resolution of an ever evolving epigenetic clock.

"There are a lot of anti-aging products out there these days — with wildly varying degrees of scientific support," said senior author Trey Ideker, professor at UC San Diego School of Medicine and Moores Cancer Center. "But how do you know if a product will truly extend your life without waiting 40 years or so? What if you could instead measure your age-associated methylation patterns before, during and after the intervention to see if it's doing anything?" Ideker led the study with first author Tina Wang, who was a graduate student in Ideker's lab at the time.

How dogs actually age (and what that tells us about how we do) | University of California

At the least, it gives me something to think about as I watch our bedhead 6 month old Golden-Doodle Faye morph over the next half year into the dog she's going to be (I know, everyone and their grandma has a doodle, but as the Marine's Rifle Creed goes: This is my doodle. There are many like it, but this one is mine.)

Image: Andrew Yi
Image: Andrew Yi