Dog Years-Comparing Human and Canine Lifespan
Brennen McKenzie
Director of Veterinary Medicine at Loyal & Veterinarian at Adobe Animal Hospital
It has long been a common simplification to say that 1 dog year = 7 human years. This relationship derives from the assumption that the average human lives seven times longer than the average dog. This is an unsatisfactory approach, however.
Human and canine life expectancy vary with multiple factors (e.g. geographic location, environmental conditions, socioeconomic variables for humans, and breed for dogs). And while the lifecycle stages of humans and dogs are similar, they occupy very different proportions of the lifespan in each species. Dogs mature and age very rapidly compared with people, who experience extremely prolonged periods of growth and development as children and, in many cases, relatively long periods of senescence.
One recent method of relating human and dog ages relies on epigenetics—the study of changes in the DNA that do not affect base-pair sequence but do influence the expression of genes. In a previous newsletter, I explored the potential for using such epigenetic changes to predict chronological age and potentially measure biological age; so-called epigenetic clocks. This same technology, applied to regions of DNA that are shared by both dogs and humans, can help us correlate the lifecycles of these two species.
Here is a better formula relating human and canine age:
human age = 16ln(dog age) + 31.
This generates a comparison between the human and dog life stages that looks something like this:
Even this relationship, of course, is only a rough approximation. Dogs of different sizes age at different rates, so while a 9 year-old Labrador might be the same age as a 65 year-old Tom Hanks, a 9 year-old Great Dane would be biologically older, and a toy breed much younger, at the same age. Tools are available that attempt to take body size into account.
While the old-fashioned methods of understanding dog year might be satisfyingly simple, researchers and dog owners benefit from newer, more accurate ways of knowing how old our canine friends really are.