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Is There a More Accurate Assessment of Your Dog's Age?

Analysis by Dr. Karen Shaw Becker

new way to calculate dog years

Story at-a-glance -

  • A not-yet-peer-reviewed study all over the news lately boasts a “new, improved” formula for calculating a dog’s age
  • On closer inspection, the new formula is more difficult for the average pet parent to use because it’s derived from a process called DNA methylation, which is now being used by human “longevity biohackers” as a means of assessing cellular and metabolic age (compared to chronologic age)
  • Because this new way of assessing cellular aging is borrowed from human longevity research, it may take time to accurately transpose the technology and interpret the results accurately for dogs and cats
  • When and if it becomes widely available for pet lovers, DNA methylation analysis may be a promising new way to evaluate how your pet is aging from a cellular perspective

Some of you dog lovers out there may have noticed an extraordinary number of recent news articles and blog postings proclaiming there's a new way to determine the age of your dog. Here are just a few examples of headlines I've run across over the last few weeks:

From LiveScience: 'Dog Years' Are a Total Myth. Here's How Old Fido Really Is."1

From Smithsonian Magazine: Calculate Your Dog's Age with This New, Improved Formula2

From Mother Nature Network: Here's a new way to calculate your dog's age in human years3

From the BBC: Dog age: New way to calculate your dog's age in human years4

From NPR: A New Way to Calculate Your Dog's Age5

All the recent news items on this topic cite a study6 conducted by a team of university researchers, the results of which appear on the bioRxiv website, which calls itself "The preprint server for biology," and looks to be some sort of clearinghouse for not-yet-peer-reviewed scientific research.

Simply put, for their study conducted at the University of California, the research team examined how dogs (over 100, between the ages of 14 weeks and 16 years, and primarily Labrador Retrievers) matured by focusing on a natural phenomenon called DNA methylation.7

Using the New Formula to Calculate Your Dog's Age Is Complicated

The "old way" as illustrated in the chart below has been and remains the best tool to guesstimate a dog's age in human years, based on his or her size and weight. The very first formula — 1 human year = 7 dog years — was replaced long ago with the more accurate averages in the chart provided by the American Kennel Club (AKC) below:8

How Old is My Dog in Human Years?

The media outlets that picked up this new story didn't expend much energy trying to provide their audience with the "new way" to calculate a dog's age. From the Telegraph:

"Multiplying the natural logarithm of a dog's age in calendar years by 16 and adding 31 will show its equivalent age in human years, the study said."9

Raise your hand if you use the natural logarithm, defined as "A logarithm to the base e (2.71828…)"10 in your daily life. Yep, me neither. And others have also voiced criticism about this formula.

New Aging Comparison Formula Has Some Critics

As one commenter to the study, "Corvus A," put it:

"Dear authors: the formula for age comparison is bunk. Your research for comparison of DNA age markers is great — but using it to create an aging comparison formula is a parlor trick. No dog at two is the mental, or physical, equivalent of a 40-year-old person. And the reduced slope of aging at advanced years, indicated by the formula, does not replicate a reasonable expectation of life experience or expectancy.

I'm going to stick with the seat-of-the-pants formula of 10 years for each of the first two, and 6 thereafter. It gives me more useful results and communicates better to inexperienced dog owners. Creating a formula based on a single data point does not a full analysis make."11

In essence, this comment is reflective of what I have seen from the animal-loving community with regard to this study: we need more research and more data before we make assumptions or conclusions, including more data from a variety of other breeds.

Another commenter to the study, "Alex Hall," made some excellent points as well, which may provide a bit of clarity with regard to why the study was conducted. One excerpt:

"… the link between methylation in dogs and canine aging is inferred too loosely. It's a correlation vs. causation issue. I would greatly appreciate if the authors could rephrase their abstract, results, and discussion to reflect that their study is on the topic of methylation in a population of dogs, rather than the cumulative effect of methylation in aging dogs.

I am concerned that the anchor author's conflict of interest jeopardizes the legitimacy of the strength of the conclusion. It would seem that there is financial incentive for this study to say a certain thing: dog age can be inferred using health data analytics.

95% of the dogs used in this study are Labradors. Though not intrinsically an issue, the generalizations made from such a homogeneous population is perplexing at a minimum."12

The section 'Fitting the epigenetic age transfer function' is being widely interpreted by non-experts as 'a new formula for aging in dogs,' but it is not really based on new understanding of the biology of dogs."

As you can see, not only is the natural logarithm formula difficult for non-mathematicians, but as Hall points out, it isn't based on new science of any kind (for people), just new data from one breed of dogs.

Most importantly, a math formula is incapable of evaluating the effects of an animal's environment, diet, stress level, activity level and genetic predispositions on his or her genome — but those diagnostics are on the horizon.

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Take Home Message: Exciting Research Pertaining to Dog Aging Is in the Pipeline, but It's Not Yet Ready for General Use

I just returned from the Broad Institute where I interviewed Dr. Elinor Karlsson from Darwin's Ark about her fascinating work sequencing dog DNA (their test kits evaluate 4 million genetic markers). This is one of many facilities around the world investigating how the genome impacts animal health, behavior and aging.

Assessing DNA methylation has become all the rage among human "longevity biohackers" as a means of assessing biologic age (compared to chronologic age). Dr. Mercola regularly hosts experts who discuss how and why methylation status and telomere length plays into aging and longevity, and why we can use it as a tool to determine how healthy we are on the inside (compared to our calendar age).

It's only a matter of time before these principles and diagnostic tools trickle down to the pet community and become widely available.

Because this new way of assessing cellular aging is borrowed from human longevity research, it will take time to accurately transpose the technology and interpret the results for dogs and cats. Currently there are only a few labs offering biological age analysis for dogs (to my knowledge, no tests are available for cats, yet).

The good news is when these diagnostic tools become widely available (and affordable) for pet lovers, DNA methylation analysis may be a promising new way to evaluate how your pet is aging from a cellular perspective, with no math required!