A Dog's Life

Since time immemorial, through tumultuous events and extraordinary inventions, one particularly popular myth has held constant: one human year is equal to seven dog years. Skeptics have often disputed this claim, noting that it is incredibly unlikely that dogs would age in the exact same manner as humans. The American Veterinary Medical Association has promulgated its own formula: the first human year is 15 dog years, the second is nine, and every year thereafter is equal to five, but the myth lived on.

A few years ago, a study of Golden Retrievers further confirmed the AVMA’s repudiation of the popular theory of dog aging, finding that dogs age rapidly in the first five years of their life, before slowing just as quickly after that time. A one year old dog was estimated at roughly 30 in dog years, a 3 year old 49, and at 8 they are 64 in dog years. As earth-shattering as this was, it was only the second biggest development in the interplay between dogs and aging in recent years. For dogs are also living longer than they used to, a fact we can all celebrate.

Unsurprisingly, our data on dog life expectancy is limited, particularly as we look deep into the past. One of the few pieces of evidence before 1900 appears to be an inscription at Westminster Abbey that compared an 81 year old man’s stage of life to that of a nine year old dog (and a 27 year old horse). Historical life expectancy is a muddled topic—an astonishingly terrible half of all children died in Medieval Europe—but we know enough to say that even the average person who reached maturity during that period did not live until 81. One estimate has 13th century English aristocrats who lived to 21 averaging a life expectancy of 64. With a decent amount of guesswork, we can conclude that a dog that lived until nine would be a rarity.

In the more recent past, we have better measures of progress on life expectancy. In 1900, fewer than 20% of dogs lived past the age of 6. In 1987, 32% did. By 2009, it was 44%. All but three of the longest living dogs in recorded history died after 2000.

Today, according to a study that produced the first life tables for dogs in the United Kingdom, life expectancy is 11.23 years at age 0. Even the dog with the shortest lifespan in the data set, the French Bulldog, has an average of 4.53 years. This is unacceptably low, raising moral questions about the continued breeding of the French Bulldog, but also illustrates how far we’ve come. If even the shortest living dog has a comparable lifespan to the average dog in 1900, that’s evidence of progress, bittersweet as it is.

Some of the life expectancy increases among dogs have been quite sudden. Another study found that between 2013 and 2019, lifespans across every size of dog increased between 4 and 7%. That means the lifespan of a medium-sized dog increased by half a year, or 2.5 dog years by the AVMA formula, in only six years. A different study found that in the U.S., dog life expectancy increased from 10.5 to 11.8 years between 2002 and 2016.

A key reason pets are living longer is higher vaccination rates. Just like among humans, vaccination against important diseases leads to healthier lives. Aside from rabies, most dog vaccines have been invented in the past several decades. The distemper virus was created in the 1950s, canine hepatitis in the 1960s, parainfluenza in the 1970s, and parvovirus in the 1980s. Today, there is a robust vaccine schedule for dogs, which includes a combination vaccine, known as DHPP, for the four diseases listed above as well as kennel cough, making it more accessible and affordable to protect dogs against the most common diseases.

There has also been a concerted effort to provide more nutritious meals to dogs. As dogs have become more and more part of the family, owners have sought better food options that extends dog lifespans and keeps them healthier. On the one hand, this has created an entire cottage industry of expensive food, but there’s no doubt that increasing investment in dog food yields positive outcomes.

In addition, there have been significant advances in veterinary medicine in recent years. Previously, in order to look inside a dogs body, a vet had to do an invasive procedure. Today, we have diagnostic tools like MRI’s, ultrasounds, and CT scans, allowing vets to use imaging to identify issues in a noninvasive way. At the same time, we now have the ability to analyze dogs’ DNA and RNA to root out infections. Specialty services are now also more readily available, with veterinarians who focus specifically on oncology, cardiology, surgery, and more.

The future of increasing dog life expectancy is also exceptionally promising. Many of the same innovations that could transform medicine among humans, from new vaccines to gene editing to AI to prosthetics, could also be available for dogs. The Dog Aging Project is an attempt to gather better data on dog health, and it involves studying tens of thousands of dogs, from their complete medical history to conducting detailed surveys to sequencing the genomes of some of the participating dogs. They are also undertaking clinical trials in order to assess the utility of different anti-aging drugs. These drugs include rapamycin, which has been effective at extending the life expectancy of flies and worms and has shown some promise among humans.

Other companies are also exploring pathways to improving dog life expectancy. The FDA agreed that a drug produced by the company Loyal was effective. This drug is intended to extend the lives of larger dog breeds, and its goal is to receive conditional approval in 2026. The company is also working on a drug that would improve life expectancy regardless of dog size. Another company, Vaika, is running trials on sled dogs, using an anti-aging drug to stop damage to DNA. In addition, a Professor of Medicine at Yale developed a cancer vaccine for dogs which is meant to spur a targeted response against tumors when they emerge. After multiple clinical trials, it appears to be effective, and is currently under review by the USDA.

It is profoundly sad how short the lives of our animal companions are. We manage to fit immense love and joy into that shorter time frame, but I suspect there are few dog owners who would not leap at the chance to extend their dogs life, especially if it also increases their quality of life as they age. We are living in a time where that is not only possible, but it has already happened. And as medicine continues to improve, both among humans and our best friends, so to will our ability to prevent illness, treat diseases, and spend more healthy, happy years with our four-legged family members.