Dogs live shorter lives than humans, and so a six-year-old dog is at a far later stage of its life than a six-year-old child. A dog can even be a grandparent at age six. What, then, is its age in “human years”? New research, published in the journal ‘Cell Systems’ has come up with a formula — and a graph — to determine that.
Was there not a formula already?
There exists a very simple thumb rule, used frequently over the years. The new research, however, has described it as a myth. According to the popular rule, you multiply a dog’s age by 7, and you supposedly get its equivalent age in human years: For example, a four-year-old dog is 28 in human years. Only, it’s not so simple.
The new research, which is based on epigenetics, has found the comparison between human years and dog years is not perfectly linear — which would have been the case had the 1:7 thumb rule been reliable. The relationship, in fact, follows the red curve shown in the figure.
How can I use this curve to determine my dog’s age in human years?
First, find your dog’s age along the horizontal (X) axis. Suppose your dog is four years old. Locate 4 on the horizontal axis, then trace your finger upwards until you reach the red curve. From that point, move left towards the vertical (Y) axis, where you have human years (illustrated with Tom Hanks at various ages). Your finger will touch the vertical axis at, in this case, 52 years.
So, a four-year-old dog is equivalent in physiological age to a 52-year-old Tom Hanks (or any 52-year-old human). This is almost twice as much the age you would get (28) if you followed the 1:7 thumb rule.
What is the basis of this new calculation?
It is based on molecular changes in the human genome and dog genome over time. Researchers at the University of California at San Diego analysed patterns over time in methylation — a term that refers to specific chemical changes in the genome.
This is the field that is known as epigenetics, which studies chemical modifications that influence which genes are “off” or “on”, without altering the original genetic sequence itself. The new formula, the researchers said, provides a new “epigenetic clock” for determining the age of a cell, tissue or organism.
How did the researchers derive the formula?
The UC San Diego team had previously published epigenetic clocks for humans. For the new study, they collaborated with dog genetics experts at UC Davis and the US National Human Genome Research Institute. They analysed blood samples from 105 Labrador retrievers for changes with age.
Indeed, that is one limitation of the new epigenetic clock, acknowledged by senior author Trey Ideker himself. (The first author is Tina Wang, Ideker’s former graduate student, who first suggested the idea for such a study.) In a statement, Ideker acknowledged that the new epigenetic clock was developed using a single breed of dog, and some dog breeds are known to live longer than others. More research will be needed, he said.
Will it work for my dog if it is not a Labrador?
Ideker said it is accurate for humans and mice, as well as Labrador retrievers. He predicts that the clock will apply to all dog breeds. As such, it may provide a useful tool for veterinarians — and even for evaluating anti-ageing interventions, the researchers suggest.
There are a variety of anti-ageing interventions in the market, with some of these standing on a more solid scientific foundation than others. But, as Ideker noted in the statement, “how do you know if a product will truly extend your life without waiting 40 years or so?”
If you refer to the new epigenetic clock, you need not wait, he suggested. “What if you could… measure your age-associated methylation patterns before, during and after the intervention to see if it’s doing anything?”
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