We’ve Been Calculating Dog Years All Wrong

When your dogs are like family it’s important for many people to note how old they’d be if they were human. The average human life expectancy is around 72 years, while for dogs this is only about 10 years. So, it makes sense to multiply a dog’s age by 7 to get roughly how they are in human years. This is a way to explain the creaky joints and slowing down that many dog parents see in their beloved animals over time.

But, experts are now saying that the whole concept of dog years isn’t accurate at all.

A study published in 2020 in the scientific journal, Cell Systems, examined how labradors age over time. The findings reveal that dogs have an epigenetic clock just like humans do. The study was led by Tina Wang of the University of California.

Researchers looked at the DNA methylation 104 labradors ages 4 weeks to 16 years. As mammals age segments of their DNA become laden down with methyl groups known as methylomes. Researchers compared the findings of the dogs methylomes against samples from 320 humans ages 1 year to 103 years.

What they found was that how to compare dogs’ ages really depends on where in their life cycle they are. It isn’t a static number. For instance they found that a 7-week-old lab puppy had similar rates of DNA methylation as a 9-month-old human baby and both are getting their first teeth around this time.

blonde lab under a table

Via: Shawn Peng/Unsplash

From there the dogs rapidly aged as they entered puberty and adulthood -at a rate much faster than humans. A 2-year-old dog had similar DNA methylation rates as 42-year-old human.

The rate of aging slowed down again once dogs were fully grown. So basically the ratio at which labradors and humans age is dependent upon how old the dog is at any given period of measurement. Researchers called this a “nonlinear relationship” between dog years and human years.

yellow lab puppies
Via: bo7mon/Flickr

The study authors explained the rate thusly:

2–6 months in dogs = 1–12 years in humans
6 months to 2 years in dogs = approximately 12–25 years in humans
2–7 years in dogs = 25–50 years in humans
12 years in dogs = 70 years in humans

The formula to determine approximate labrador ages relies on a natural logarithm. Enter your dog’s age in here and then multiply that by 16. Then add 31 to get the approximate age in human years of your dog. Using this formula a 4-year-old dog would about 53-years-old in human years i.e. [16ln(dog_age) + 31].

black lab with a chew toy
Via: Trevor Chown/Unsplash

The study of DNA methylation rates is in the field epigenetics. This new line of research has been gaining steam over the past decade and seeks to understand how and why we age or develop illnesses when someone in the same family might age or express illness differently.

little dog in cone of shame

Via: Joel Caceres/Flickr

Unlike genetics, which looks at what DNA you’re born with, epigenetics can help scientists understand how our environment can alter how are genes are expressed. Labradors were chosen for the study because they are a common dog breed and because they are pets that have access to health care, much like humans do. Factors like stress, diet, and injury can all affect how any animal ages over time, something that can make determining dog years even harder.

For a better view of how dogs age, a study involving various breeds of dogs may give a clearer answer to just how our canine friends age over time as compared to humans. But, for now there simply isn’t a universal dog years calculator.

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