You may need to rethink your dog’s age. Conventional wisdom says that one human year is the equivalent of seven dog years, but a new analysis suggests we have been getting this all wrong.
The seven dog years to every human year rule comes simply from crudely dividing human lifespan, around 80 years, by dog lifespan, typically 12 years. Trey Ideker at the University of California, San Diego, and his colleagues found that the rule is a little off.
The team performed a genetic analysis of dogs and humans to identify how they age over time. The researchers discovered that compared with humans, dogs age faster at first, blazing into the equivalent of human middle age after only a few years.
But this ageing quickly tapers off, with the next 10 years only accruing two human decades’ worth of changes. The team put this together into a single formula plotted in the graph below: human_age = 16 ln(dog_age) + 31. It is a significant revision to our understanding of how to map dogs against their human owners in terms of age, says Ideker.
The team studied 104 Labradors, ranging from very young puppies to 16-year-old dogs. The researchers then compared the dogs’ methylomes – a set of chemical changes to genes that fluctuates throughout life – to those of humans over a lifetime. By matching these methylomes, the researchers could convert between the physiological age of dogs and humans.
In both, these age-related changes happened largely with developmental genes found in all vertebrates that are important from their time in the uterus through childhood.
“You have these major changes [to the methylomes] that go on during development when you’re growing and then, as you age, you’re kind of looking at the afterburn,” says Ideker. “That afterburn is what’s associated with ageing.” The research could inform when to start looking for common, age-associated diseases in dogs, he says.
The researchers also looked at the methylomes of mice. They found that two-and-a-half mouse years translates to about nine dog years, suggesting that this tool might be able to convert ages across many mammal species.
Matt Kaeberlein at the University of Washington in Seattle says it would be interesting to find out what happens to the age clock in dog breeds with very different lifespans, such as Great Danes and chihuahuas.