One human year equals seven dog years, right?
Not quite.
Dog owners have been using the 1:7 ratio to calculate their pup’s age for centuries, but a new DNA-based study suggests that canine aging is not that simple. It’s also not the first study to complicate the popular formula, which doesn’t account for a dog’s breed or the environment in which it lives.
Dogs age rapidly when they’re born but the process slows down later in life, according to the recently-released research paper from University of San Diego. Their findings show that a dog’s lifespan isn’t always proportional to a human’s.
Researchers behind the new paper examined the DNA in 104 Labrador Retrievers at different ages, noting how a genetic process called methylation progressed over time. This process is used to measure humans’ ages in a test called an epigenetic clock.
The UC San Diego team ran the epigenetic clock test on dogs, then compared the results to tests from 320 humans and 133 mice.
The paper’s authors found a “non-linear relationship which translates dog to human years.” In other words, some phases of a dog’s life are proportionally shorter or longer than the same phases in humans.
Based on their findings, researchers developed a new formula that they say more accurately lines up with the major milestones like infancy and old age.
The new formula isn’t easy to do in your head, but you can calculate it on your phone. You may have to turn the phone sideways to get the full calculator keyboard, because you’ll need the ln button (logarithm) to do it.
Here’s the formula:
16 x ln(dog’s age) +31 = human age.
Or, if you’re plugging it into your calculator:
Type your dog’s age. Press ln. Press x and type in 16. Press + and type in 31. Hit the ‘equals’ sign.
The result will be your dog’s age in human years.
If you’re not into the math, just know that a one-year-old dog is the same genetic age as a 31-year-old human, even if they still act like a puppy. Dogs enter their human “sixties” at age 7, their “seventies” at age 12 and their “eighties” at age 22.
The study authors acknowledge that the formula might play out differently for other species of dog. They chose one breed for their tests because it was easier to compare their DNA, since there was less variation.
The paper has not yet been peer reviewed, meaning other scientists haven’t examined it to make sure it’s completely sound.
However, the paper appears to echo the current scientific understanding of canine aging, based on information from the American Veterinary Medical Association (AVMA).
“Contrary to popular belief, dogs do not age at a rate of 7 human years for each year in dog years,” The AVMA says on its website.
Larger dogs tend to age more rapidly, while smaller dogs often live longer, according to the American Kennel Club. That means the new formula will probably be more accurate for dogs that are approximately the same size as a Lab Retriever.
UC San Diego isn’t the only school studying the way dog’s age. The University of Washington and Texas A&M University just launched a long-term study called the Dog Aging Project, in which researchers will monitor how dogs age year-by-year. The schools are still recruiting dogs (and their owners) in hopes of monitoring 10,000 canines over time.
“The goal of the Dog Aging Project is to understand how genes, lifestyle and environment influence aging,” the site says.
The U.S. National Institute on Aging is funding the US$23-million project because dogs share the same environment as humans. They also get many of the same diseases.
“What we learn will potentially be good for dogs and has great potential to translate to human health,” said project co-director Daniel Promislow of the University of Washington School of Medicine.
Veterinarian Leslie Lambert says she hopes the researchers will learn some valuable insights from dogs like Oscar, her 11-year-old rescue whom she has already enrolled.
“I would selfishly like to have him around forever,” Lambert told the Associated Press last week. “Unfortunately, he ages much, much faster than I do.”