Calculating your dog’s age in human years is simple, right? You convert one dog year into seven human years, and that gives you an idea of how old your dog really is in terms of the way we understand our own aging. But maybe it isn’t that simple.
A recent study by a team of scientists including geneticists and biologists at the Department of Medicine at University of California San Diego have challenged this assumption by coming up with a more accurate way to determine a dog’s age in relation to human years.
This research turned to DNA methylation to determine age. The method takes into account the impact of lifestyle and health as it acts directly on the DNA to determine the comparative biological age of a dog as we understand aging in human terms. In mammals, as we get older, methyl will attach to DNA. Methylation happens on a pretty consistent, linear rate, making it easy to determine someone’s age.
“In terms of using DNA methylation to predict age within species, DNA methylation tends to be the best molecular change that predicts age reproducibly in many distinct animals and in various tissues,” says Tina Wang, lead biologist and author of the study.
To compare dog years to human years, scientists examined DNA samples from 16 Labrador Retrievers over the course of 16 years. The research studied the physiological timings of events in the DNA that occur over the years and translated into human years that by using the average lifespan of these two species. They compared changes in the dog’s DNA over time to the previously collected DNA of 320 humans between the ages of one and 103.
“We identified a conserved molecular signature of age between dogs and humans,” says Wang. “Using this signature, we can match the age of each dog to the age of its nearest human, thereby creating a quantitative translation of dog years to human years.”
It was discovered that the aging process is accelerated in dogs during their younger years. So, a one-year-old dog is actually 31 and a two-year-old dog is 42; whereas, an 11-year-old senior is 69 and a 14-year-old is 73.
The equation the researchers are using is multiplying the natural logarithm of your dog’s age by 16 and adding 31. It looks like this: human age = 16ln(dog age) + 31
Seems way too complicated? Here is a dog age calculator you can use, where you just punch in your dog’s age.
If you’re wondering how this translates to breeds that tend to have a longer lifespan, like small breeds, Wang admits it’s “an open research question.” The researches expect that smaller dogs could potentially reveal different progressions in their DNA according to their life expectancy when comparing them to humans.
“Since small dogs like Chihuahuas get to live much longer than Labradors Retrievers, they can be sampled in higher numbers at much older ages, and this would change the trajectory of the curve,” says Wang. “It is unclear what the amount of change might be when comparing to humans, [who] are extremely long-lived. However, among dogs, this effect should be significant.”
This method of determining age may be especially helpful in dogs with unknown birthdates, says Wang. Veterinarians have typically looked at the condition of a dog’s teeth to estimate age, but factors like care and genetics can alter dental health significantly.
“To further improve this method, it would be nice to see the differences when using dogs of different sizes, and also use many more dogs, spanning across multiple breeds,” says Wang. Considering the high energy typical of a dog at two years old, it remains to be seen if this method turns out to be any more accurate than other methods.