Sad Birthday: No Wishes, Only Pain

A team of researchers has recently debunked the myth that one year in humans is equivalent to seven in dogs. They have come up with a formula that is based on changes in DNA.
It has been widely believed that for every year a person ages, a dog ages seven years. No one knows where this idea came from, but it has been accepted as truth without question.

However, a team of researchers from the University of California in San Diego (United States), as cited by Science Alert, has published a more scientific version of the story based on the evolution of DNA in the scientific journal bioXriv.
The method is based on an epigenetic mechanism called methylation. As both humans and domestic dogs age, methyl groups are added to our DNA molecules, which can alter the activity of a DNA segment without changing the DNA itself. Through this process, one can determine the age in humans; this is known as an epigenetic clock.

In this way, geneticists Tina Wang and Trey Ideker set out to compare the epigenetic clock of humans with that of dogs. Considering that the lifespan of dogs, depending on their breed, can vary significantly: 6-7 years for some large breeds like mastiffs to as long as 17-18 years for breeds like chihuahuas.

Hence, they chose to use the Labrador retriever dog for the study, as this breed shows a high level of genetic homogeneity, making it easier to identify genetic factors associated with complex traits such as aging. The methylation profiles of Labrador retrievers were compared to those of 320 humans aged between one and 103 years, as well as to those of 133 mice.

According to researchers, when comparing dog methylomes to human methylomes, a non-linear relationship was revealed that translates a dog’s age to human years. The similarities were greater when comparing young dogs to young humans, and older dogs to older humans.

This alignment of epigenetic clocks allowed the team to create a formula to calculate a dog’s “human” age: human age = 16ln(dog age) + 31. Here, “ln” represents the natural logarithm. So, you need to multiply the natural logarithm of your dog’s age in years by 16 and then add 31. This will give you the dog’s age in “human years.”

Using this formula, certain milestones align quite well. Seven weeks in dogs corresponds to nine months in humans, the time when baby teeth are erupting in puppies and infants. The average lifespan of the two species also matched up: 12 years for Labradors and 70 for humans.

However, other milestones do not align as smoothly. Dogs, for instance, go through puberty and reach sexual maturity faster than humans, so the period between adolescence and middle age does not quite match up. Nevertheless, the process of methylation in dogs slows down as they age, bringing humans back on par with them.

Even though this formula may not be applicable to all dog breeds, it is true that it is more “scientific” than simply multiplying by seven, as it is based on our epigenetic clock. This information was shared by both El Confidencial and Gizmodo.

The formula developed by the researchers sheds light on the intricacies of canine aging and provides a more accurate way to measure it compared to the long-held belief of the “seven-year rule.” It also emphasizes the importance of understanding biological processes rather than relying on simplistic assumptions. However, while the findings are groundbreaking, they also highlight the complexity of applying a universal formula across all dog breeds.

For instance, smaller breeds like Chihuahuas tend to live longer than larger breeds such as Great Danes. These differences suggest that while the formula works well for Labradors, adjustments may be necessary for other breeds. Each breed has unique genetic and environmental factors influencing its lifespan and aging process. Future studies may expand this research to include a broader range of breeds, which would make the formula more widely applicable.

The insights gained from this study are not just academic; they have practical implications for pet owners and veterinarians. By better understanding a dog’s “human age,” owners can make more informed decisions about their pet’s care. For example, knowing when a dog enters its “senior years” could guide choices regarding diet, exercise, and veterinary checkups. Similarly, veterinarians could use this information to recommend age-appropriate preventive measures or treatments.

Moreover, the study opens the door to further exploration of the epigenetic clock in other species. The use of methylation as a biological marker for aging could revolutionize how we study aging across the animal kingdom. It could also lead to new breakthroughs in understanding age-related diseases and developing treatments that benefit both humans and animals.

One fascinating aspect of this research is how it underscores the similarities between humans and dogs. Despite our many differences, dogs have lived alongside humans for thousands of years, evolving alongside us in many ways. The alignment of epigenetic clocks in young and old dogs with their human counterparts speaks to a deep biological connection, further solidifying the bond between these two species.

For pet owners, this research might inspire a new perspective on their furry companions. Understanding that a two-year-old dog has the biological maturity of a 42-year-old human, for instance, could change how owners view their pet’s behavior and needs. Similarly, recognizing the slower pace of methylation in older dogs could lead to greater patience and care as pets age gracefully.

While the formula is a step forward, it’s also a reminder that science continues to evolve. As researchers gather more data and refine their methods, our understanding of canine aging—and perhaps aging in general—will likely deepen. Until then, pet owners can appreciate the nuanced approach offered by this study, which honors the complexity of their dogs’ lives and emphasizes their unique aging journey.

In the end, this research is not just about numbers or formulas. It’s about fostering a deeper understanding of the animals that share our lives and ensuring that we provide them with the best care possible. By recognizing the stages of their lives more accurately, we can strengthen the bond we share with them, ensuring they live happy, healthy lives. For anyone who has loved a dog, this research serves as a reminder of the preciousness of every moment we spend with them, regardless of how we calculate their age.