Common wisdom has long held that each dog year is equivalent to seven human years. But a new equation developed to measure how a dog ages finds the family pup may be a lot older than we realize.
Researchers studying chemical changes to canine DNA found that dogs age very quickly during their first five years and much more slowly later on.
The findings, published recently in the journal Cell Systems, calculate that a 5-year-old dog would be pushing 60 in human years.
“Puppies age super quickly,” said Trey Ideker, the study’s senior author and a professor of genetics at the University of California, San Diego, School of Medicine. “By the time a dog is a year old, at a molecular level, he’s much more like a 30-year-old human. Retrospectively, we did know these things. It didn’t make any sense that the equivalent to a 7-year-old human would be able to have puppies.”
Ideker and colleagues noticed that dogs, just like humans, have chemical marks on their DNA, called methylation marks, that change with age.
“The genome itself doesn’t change with age,” Ideker said. "What does change is marks on the genes that control a dog or human's growth pattern."
The methylation marks, or as Ideker calls them “wrinkles on the genome,” change in predictable ways as we and dogs age.
“We are able to quantify this at the molecular level and tell how fast someone is aging, and we can align it across dogs and humans,” Ideker said. “But we don’t know exactly what it all means.”
To find the mathematical relationship connecting dog aging to human aging, Ideker and his colleagues studied 104 Labrador retrievers whose ages ranged from weeks-old puppies to 16-year-old dogs.
When they compared the dog DNA data to information from humans, the researchers came up with a new equation to figure out the dog's comparable human age.
The equation: 16 ln(dog age) + 31 = human age.
For iPhone calculators that have the natural logarithm, or "ln," function, first type in the dog's age. Then hit the "ln" button. Multiply that result by 16; then add 31.
If you're using Google’s scientific calculator: First, hit "ln," then type in the dog’s age, then equal it out. Next, multiply by 16, and then add 31.
Using that equation:
- a 1-year-old dog is like a 31-year-old human;
- a 3-year-old dog is like a 49-year-old human;
- a 7-year-old dog is like a 62-year-old human.
By this time, dog aging has slowed down, so an 8-year-old dog is like a 64-year-old human.
According to this equation, the average 12-year Labrador lifespan is equivalent to a human living to about 70.
Ideker suspects there will be some variation based on dog breed but that they will all follow a similar pattern.
The new dog-age math has given Ideker some pause when he thinks about taking his own dogs on runs: He now realizes his 6-year-old dog is actually pushing 60 in human years.
Margret Casal, a specialist in veterinary genetics, said the new calculations match what she’s observed in her dog patients.
“It validates what a lot of other researchers have been saying,” said Casal, a professor of medical genetics, pediatrics and reproduction at the University of Pennsylvania School of Veterinary Medicine.
Researchers knew the 1-to-7 comparison was off, but they did not know what the specific relationship was, she added.
“It will be interesting to look at different breeds," Casal said. "We know that some smaller breeds live longer and some larger ones don’t live quite as long.”
For owners hoping to help a beloved dog live as long as possible, Casal offered a few tips:
- Feed them a high-quality food, preferably one that is approved by the Association of American Feed Control Officials. And don’t feed too much: Lean dogs tend to be healthier ones.
- Give your pet proper preventative health care, such as flea and tick control, heartworm prevention and vaccinations.
- Make sure your dog gets aerobic exercise. “Take your dog for reasonable walks,” Casal said. “How far you walk depends on how far they want to walk and are able to walk. And don’t overdo it with puppies: It’s bad for their joints.”
- Introduce exercises that help develop balance and core muscles, especially as dogs age.
Lastly, take your dog for yearly wellness visits.
“That’s really important,” Casal said. “I can say as an owner of a dog, sometimes you don’t see something is wrong and your vet might be able to see it better.”