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Seven-year hitch: comparing 'dog years' to humans is barking up the wrong tree


A dog’s life: A one-year-old dog is similar to a 30-year-old human, said scientists. Photo: Getty

A dog’s life: A one-year-old dog is similar to a 30-year-old human, said scientists. Photo: Getty

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A dog’s life: A one-year-old dog is similar to a 30-year-old human, said scientists. Photo: Getty

The accepted wisdom among dog owners is that if you want to know how old your pet is in human terms, you simply multiply its age by seven.

It can then be decided whether man's best friend is acting up because it is a naughty teenager or simply owing to poor training.

However, research has found that this method is not based on science, and our pets may be far "older" than we previously believed.

As people and animals age, the number and placement of methyl groups in the genome change. By mapping these, scientists can tell the age of an organism.

Researchers at the University of California San Diego School of Medicine used blood samples from 105 Labrador retrievers to accurately determine how quickly the breed ages.

The study, published in the 'Cell Systems' journal, found the human/dog age comparison does not follow the 1:7 ratio over time. Especially when dogs are young, the researchers found that they age rapidly compared to humans.

A one-year-old dog is similar to a 30-year-old human. A four-year-old dog is similar to a 52-year-old human. Then by seven years old, dog ageing slows, and a 12-year-old dog is about 70 in human years.

"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 senior author Dr Trey Ideker of the UC San Diego School of Medicine.

Scientists argue that this new comparison between dog ageing and humans could be helpful for vets, so they are able to determine whether illnesses in dogs are age-related.

The formula provides a new "epigenetic clock", a method for determining the age of a cell, tissue or organism based on a readout of its epigenetics, which are chemical modifications like methylation that influence which genes are "off" or "on" without altering the inherited genetic code.

Previous studies have found epigenetic clocks for humans, but these do not translate to other species and may not even be the same for other humans.

One limitation of this clock is that researchers only used blood from Labradors, while different breeds have different life expectancies.

Dr Ideker plans to test more breeds, but said that since it is accurate for humans and mice as well as Labrador retrievers, he predicts the clock will apply to all dog breeds. "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," said Dr Ideker.

He said dogs were interesting to study because they live so closely with humans, perhaps more than any other animal, so a dog's environmental and chemical exposures are very similar to humans, and they receive nearly the same levels of healthcare.

The research could be useful for humans, not just their pets.

The scientists believe the epigenetic clock could be used to test anti-ageing treatments, to see if they had made any difference to the methylation patterns in the genome and therefore altered the "age" of human cells.

"There are a lot of anti-ageing products out there these days - with wildly varying degrees of scientific support," Dr Ideker said. "But how do you know if a product will truly extend your life without waiting 40 years or so?"

Irish Independent