Most dog lovers have heard the old adage that one human year is equal to seven years for our canine friends.

Scientists at UC San Diego say they have debunked that myth — and created a better model for people to properly age their pups. Their study is published today in Cell Systems.

The project started in 2014 when then-graduate student Tina Wang adopted a dog. She didn’t know how old her rescue pet was and wasn’t sure how to respond when people at the dog park asked her about her dog’s age. 

Humans, dogs and other animals all have methyl groups, which are chemical markers on DNA, that govern genes. Methyl groups change as an animal ages, acting as a genetic clock. Previous research has found that the age of a human can be reliably calculated by looking at methyl groups from the person’s cells.

Trey Ideker, Wang’s advisor and a medical professor, was already conducting research on human aging with methyl groups.

Wang started wondering if the genetic clock provided by the methyl groups could be used to age dogs.

“I realized a subset of the population would be really interested to know how old their dogs are,” she said. “I know I was.”

She brought the idea to Ideker, who was excited to fund it.

Wang analyzed the patterns of methyl groups for 104 Labrador retrievers at a range of ages, from puppies to elderly dogs. By comparing the dogs’ methyl groups at different ages to corresponding methyl groups for humans of different ages, she was able to make a graph which translates dog age to equivalent human age.

Ideker said the actual relationship between dog and human age is much less linear than the one-to-seven rule would have us believe. Instead, dogs age rapidly for the first few years of their lives. He said the methyl patterns of a one-year-old dog is more similar to those of a 30-year-old person than a seven-year-old person. As dogs get older, they age more slowly.

Since Wang’s study focused on Labradors, Ideker said the aging curve might be different for other dog breeds. He said one possible next step is to align the curves of different breeds to see what the differences are in aging between different dogs.

Scientists are also researching methyl groups to see what lifestyle changes might be able to slow aging, said Ikeder. He said there is evidence that calorie-restricted diets slow aging in a number of vertebrates.

This sort of research comes with risks. Ikeder said one concern is that insurance companies could try and use methyl groups to predict people’s health. But he said there is a lot of room for good, if the research can help doctors help people age healthily.