Accepted wisdom has it that to work out a dog’s age in human years you just multiply it by seven.
Apparently, it’s not that simple. According to researchers from the School of Medicine at the University of California San Diego, you also have to take account of molecular changes in the genome over time.
Trey Ideker and Tina Wang say there is no perfect linear comparison between dog and human age because the species age at different rates over their lifetimes.
They developed a new formula based on the changing patterns of methyl groups in genomes – how many of these chemical tags there are and where they’re located – then created a graph they say helps make a quick canine conversion.
It suggests that dogs age rapidly early and are close to 30 by the time they are one. By four they are similar to a 52-year-old human, but things slow by the time they get to seven
“This makes sense when you think about it; after all, a nine-month-old dog can have puppies, so we already knew that the 1:7 ratio wasn’t an accurate measure of age,” says Ideker, the senior author of their paper in the journal Cell Systems.
He and Wang collaborated with dog genetic experts for their study and used blood samples from 105 Labrador retrievers. They acknowledge the limitations of working with just one breed, and now plan more tests to see if their map holds up.
The new formula utilises epigenetics – the study of changes in organisms caused by modification of gene expression rather than alteration of the genetic code itself.
Epigenetic changes provide clues to a genome’s age, much like wrinkles on a person’s face, Ideker says, and their new “epigenetic clock” is transferrable across species.
And it could even prove useful for anti-aging interventions for humans.
“There are a lot of anti-aging products out there these days, with wildly varying degrees of scientific support, but how do you know if a product will truly extend your life without waiting 40 years or so?
“What if you could instead measure your age-associated methylation patterns before, during and after the intervention to see if it’s doing anything?”
Ideker adds that the study has led him to see his own canine companion in a different light.
“I have a six-year-old dog. She still runs with me, but I’m now realising that she’s not as young as I thought she was.”
Amelia Nichele is a science journalist at The Royal Institution of Australia.
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