‘Dog year’ theory is a myth, scientists find after developing new method to compare human-canine ages

New study finds that a one-year-old dog is closer in age to a 30-year-old human, while a four-year-old dog is equivalent to a 52-year-old human. Kate Ng reports

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The theory that one dog year is equivalent to seven human years has been debunked, said scientists who claim to have developed a more accurate formula to compare the ages of dogs and human.

US researchers based their findings on a new concept in ageing research called the ‘epigenetic clock’, which tracks a person’s biological age through DNA tags which change in pattern during the course of life.

The biological age can lag behind or exceed chronological age depending on an individual’s DNA tags, which are affected by chemical processes. It was discovered by German biomathematician Steve Horvath, who published his findings in 2013.

To understand more about how dogs age, the researchers gathered blood samples from 105 Labrador retrievers and sequences the genomes, or genetic material, of the dogs to track a process known an DNA methylation, which many species undergo as they get older.

The findings, published in the journal Cell Systems, revealed that the canine epigenetic clock ticks much faster than the human one, particularly in the animals’ younger years.

Dr Trey Ideker, a professor at the University of California and one of the authors of the study, said dogs were an interesting area of research because they live closely with humans, with similar environmental and chemical exposures.

The study found that a one-year-old dog is closer in age to a 30-year-old human, while a four-year-old dog is equivalent to a 52-year-old human.

The findings made Dr Ideker realise his own six-year-old dog is not as “young” as he thought she was even though she still goes running with him.

“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,” said Dr Ideker.

He acknowledged that one of the limitations of the canine clock is that it was developed using only one dog breed. Some breeds live longer than others – for example, the average lifespan of a Labrador retriever is between 10 to 14 years, while a corgi’s life expectancy is between 12 to 15 years.

Larger breeds like labradors typically have shorter lifespans than smaller dogs (iStock)

He plans to test more breeds, but predicted the clock will apply to all because it is “accurate for humans and mice as well as Labrador retrievers”.

The methylation-based formula for calculating age could also be useful in testing anti-ageing treatments, said the researchers.

“There are a lot of anti-ageing products out there these days – with wildly varying degree of scientific support,” said Dr Ideker. “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?”