Labrador

The new method of calculating the human-equivalent age of a dog was determined using Labrador retrievers.

Our Scotch collie, Buckaroo, is just shy of 14 years old. Following the long-debunked but still popular idea that one dog year equals seven human years, he’s almost a centenarian. (This “formula” may be based on average life spans of 10 and 70 years for dogs and people, respectively.) Now, researchers say they have a new formula to convert dog years to human years—one with some actual science behind it.

The work is based on a relatively new concept in aging research: that chemical modifications to a person’s DNA over a lifetime create what is known as an epigenetic clock and a process known as DNA methylation.

Other species also undergo DNA methylation as they age. Mice, chimpanzees, wolves, and dogs, for example, all seem to have epigenetic clocks. To find out how those clocks differ from the human version, geneticist Trey Ideker of the University of California, San Diego, and colleagues started with dogs. Even though man’s best friends diverged from humans early in mammalian evolution, they’re a good group for comparison because they live in the same environments and many receive similar healthcare and hospital treatments.

All dogs—no matter the breed—follow a similar developmental trajectory, reaching puberty around 10 months and dying before age 20. But to increase their chances of finding genetic factors associated with aging, Ideker’s team focused on a single breed: Labrador retrievers.

“We already knew that dogs get the same diseases and functional declines of aging that humans do, and this work provides evidence that similar molecular changes are also occurring during aging,” says Matt Kaeberlein, a biogerontologist at the University of Washington in Seattle.

The resulting dog age conversion is a bit more complex than “multiply by seven.” The new formula says a canine’s human age is equal to (and this is a little complex...) the natural logarithm of the dog’s real age, multiplied by 16, with 31 added to the total.

Using that formula, dogs’ and humans’ life stages seem to match up. For example, a 7-week-old puppy would be equivalent to a 9-month-old human baby, both of whom are just starting to sprout teeth. The formula also nicely matches up the average life span of Labrador retrievers (12 years) with the worldwide lifetime expectancy of humans (70 years).

So, how does our Buckaroo fare? Happily, the epigenetic clock calculation goes in his favor. He’s now only 73 in human years—and a spry 73 at that.

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