A senior citizen by age four/Craig Medred photo
Leave it to science to mess up that belief your 4- or 5-year-old dog is in the prime of life and should be a top-level performer for years to come.
After tracking methylomes in people and a pool of Labrador retrievers, a team of researchers from the University of California San Diego has judged as so much hooey that old idea that one year’s in a dog’s life equals seven years in a human’s life.
Dogs, they say, mature much faster than was formerly believed and age rapidly through their first three years of life. By age four, the researchers contend, the average dog is beyond middle-age. The researchers put the animal in its early 50s in human years.
The study published earlier this month at bioRxiv, a preprint server, has yet to be peer-reviewed. But it’s been rocking the dog world with its observations on how fast dogs mature.
In the first three years of a dog’s life, it appears to be aging at a rate of 12 to 13 human-years per dog-year, but dogs do not age in a direct line, according to the study. They age on a curve which begins to flatten after age four.
Beyond that date, it takes the average dog another seven years to reach the human equivalent of 70. In this period, each dog year is equal to only about two and a half human-years.
Still what is most startling about the study is the suggested rapid maturation of dogs. Front-running Iditarod Trail Sled Dog Race competitors who seem to have been running younger and younger teams every year might have stumbled onto a simple reality of canine development.
The study puts a year-old dog at about 30 in human years. That’s about the age at which human marathoners have been found to peak with their top performance years considered to be between ages 20 and 35.
A 2013 study of Ironman Hawaii competitors also found them peaking slightly later. And the Ironman, which throws a variety of physical challenges at competitors, might be more like the up, down, wet, dry, wind-battered, sometimes-tough-trail Iditarod than a marathon on well-maintained roads.
If the UC-San Diego study is to be believed, the canine equivalent of a 32-year-od Ironman (or Ironwomen) would be about a year and a half.
The study’s chart of dog years versus human years/bioRxiv
Not just dogs
Accidental discoveries sometimes being the most interesting part of science, it is worth noting the UC-Davis researchers weren’t really trying to sort out the old, old question of dog years to human years.
What they were trying to do was determine if methylomes – the markers left by the methylation that drives activity in the DNA that carries the genetic code of life for all living things – can be used to measure aging.
“Here, we map common epigenetic changes experienced by mammalian genomes as they age, focusing on evolutionary comparisons of humans to dogs, an emerging model of aging,” they wrote, and the “results establish methylation not only as a diagnostic age readout but as a cross-species translator of physiological aging milestones.”
The 104 Labradors in their study, they reported, displayed changes in both physiology and methylation that could be tracked and charted similarly to with humans.
“The observed agreement between epigenetics and physiology was particularly close for infant, juvenile and senior stages,” they wrote. “For instance, the epigenome translated seven weeks in dogs (0.13 years) to nine months in humans (0.75 years), corresponding to the infant stage when deciduous teeth erupt in both puppies and babies.
“In seniors, the expected lifespan of Labrador retrievers, 12 years, correctly translated to the worldwide lifetime expectancy of humans, 70 years. For adolescent and mature stages, the correspondence was more approximate, with the epigenome showing faster changes for dogs, relative to humans, than expected by physiological tables.”
Most dog owners, already inclined to think their canine friends age too fast, will probably be unhappy to read the news on rapid aging, but the study did suggest there might be something they can do to increase canine life expectancy.
If methylation patterns truly track the physiological progression of an organism’s life and not just chronological time, the researchers hypothesized, “the pattern should respond to interventions that slow or delay aging, such as anti-aging treatments.”
Two of those anti-aging treatments are well-documented in mice: dwarfism and caloric restriction. (The former is vividly notable in dogs with some small breeds having, on average, life spans two to three times longer than large breeds.)
“When applying the development clock to mice treated with lifespan-extending interventions,” they reported, “the epigenetic ages were 30 percent less, on average, than those of control mice. These same results were observed when using the development clock trained in dogs to predict mouse age. Together, these results demonstrate that the methylation states of developmental gene modules track the physiological effects of aging and aging interventions in multiple mammalian species.”
For science, the authors of the study claimed something of a breakthrough.
“Our study has demonstrated that the methylome can be used to quantitatively translate the age-related physiology experienced by one organism (i.e. a model species like dog) to the age at which physiology in a second organism is most similar (i.e. a second model or humans),” they wrote “These results create the opportunity to use the methylome not only as a diagnostic readout of age (as per the epigenetic clock) but for cross-species translation of physiological state. Such translation may provide a compelling tool in the quest to understand aging and identify interventions for maximizing healthy lifespan.”
For dog owners, the takeaway might be simpler:
Fido ages pretty fast already, and you’re not doing him/her any favors by offering extra treats. Every study out there has agreed that when it comes to keeping dogs healthy, it is better to underfeed them to overfeed them no matter how hard that might be to do given that many canines are world-class beggars.
And there is now evidence that underfeeding will help them live longer as well.
