Amanda Maxwell

Mar 23rd 2022

How Do Dogs Age?


Dogs were the first animals domesticated by people, and Psychology Today notes that this may have happened between 20,000 and 40,000 years ago. Apparently, sharing surplus meat with wolves started off the whole process. Since then, we’ve been sharing living space with them as pets and working animals. Nowadays, as pet owners try to understand the life cycle of their pets, they may wonder — how do dogs age? A human lifetime will see many of our canine sidekicks come and go since the lifespan of a dog is much shorter than the average human.

How Do Dogs Age?

All animals age. The aging process marks physical changes as a body grows, matures and then declines. There are transitions through various life stages that mark the passage of years. Early stages from birth and infancy show development and maturation to adulthood. Thereafter, the physical body starts to decline into senescence, eventually leading to death. Aging is a factor of life — a sort of wear and tear on the body until it can’t take anymore.

This is reflected at the cellular level, especially in structures known as telomeres. These genetic endcaps to our chromosomes protect DNA replication but are lost with aging. Eventually, they become too short and DNA replication stops, forcing the cell into senescence. According to a study published in Cell Reports, this happens in dogs as well as in people

Matching Human Years to Dog Years

In an effort to understand the aging process and life span of the family pet, many people associate a dog year or age as equivalent to seven full human years, though the American Kennel Club suggests this might not be so. It’s not very clear where this mythical form of dog chronology came from, but it may be from comparison between the human average life span of 70 years and that of the dog at around 7 years. In other words, a two-year-old Labrador is seen as a teenager of 14 years whereas only a few years later, converting human years to dog years shows that it hits middle age.

Obviously, since dogs live fewer years than people, they age faster. They reach full adult size and sexual maturity in only a few years after birth, whereas humans are still growing and maturing through their teen years. So, the question isn’t really “how do dogs age” but more — how quickly do they age? Is there a way to match human years to dog years?

A New Algorithm for Converting Human Years to Dog Years

There are some drawbacks to matching human years to dog years at the rate of 7:1. For one thing, sexual maturity arrives between 6 and 12 months in dogs. There’s also a wide variation in dog lifespans; smaller breeds age slower and live longer than larger breeds.

In an article published by The Conversation, author Christian Yates describes recent research into aging in dogs, where scientists have suggested a new formula for calculating your pet’s age: human equivalent age = 16 x ln(dog’s chronological age) + 31.

In this formula, “In” represents the natural logarithm. As Yates explains, the first dog year is equivalent to 31 human years. He adds, “Then, every time the dog’s chronological age doubles after that, the number of equivalent human years increases by 11.”

Genetic Clocks

In the Cell Report study, researchers looked at telomeres in dogs and found that they shorten at ten times the rate they do in people. Dog cells run out of life a lot faster than our cells; telomere length was a strong predictor of lifespan across many different breeds.

The most recent study that created the new algorithm used another epigenetic clock to answer the question, how do dogs age? Published in Cell Systems, the study explains how researchers compared DNA methylation patterns between humans and dogs. The National Institute on Aging also describes how the scientists examined the methylome to track DNA methylation over time in 104 Labrador retrievers of various ages.

As people age, more methyl groups are added to DNA, which silences or turns off various genes. Wired describes how researcher Steve Horvath used methylation and demethylation levels in our cellular genome as a way to measure cellular aging. When researchers examined the dog genomes, they found that as with people, canine methylation levels also changed with age. Using these changes to line up human and canine developmental milestones, the research team could then match age and stage and create the new algorithm.

All this suggests that your dog matures a lot faster than expected initially, and then the process slows down. Not only does this help to explain why your dog might not want to chase a ball so much after a certain age, but it could also push studies on human aging further forward. Examining the epigenetic clock in other species and matching it to our life cycle could help research on human aging.

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