The curiosity to compare the age of animals with that of humans is very widespread and the most frequent case undoubtedly concerns dogs. We often find ourselves interpreting the age of our four-legged friend using typically human parameters, in an attempt to understand what stage of our life his corresponds to. Recent research conducted by a group of geneticists at the University of California has shown that dogs, a bit like humans, do not age at a constant rate over time. Through studies on the DNA of a sample of 104 Labrador retrievers of different ages, the team of researchers developed a mathematical formula that allows the dog’s age to be compared with human age. The formula is Human age = 16 × ln(Dog age) + 31where “ln” is the natural logarithm of the dog’s age. Obviously this is an approximation and, at the moment, the studies have been conducted on only one dog breed, but they open new avenues to knowledge on the aging processes of dogs, but also of other species.
The new method of calculating the age of the dog
The team of researchers at the University of San Diego in California took a look 104 Labrador retriever dogs of different origins and of different age classes, from puppies to 16-year-old elderly dogs, comparing them with a sample of the human population of 320 individuals aged between 1 and 103 years. The biological process underlying the study is a molecular alteration that occurs during the aging of an individual and is the chemical reaction of DNA methylation: in practice a chemical group composed of a carbon atom linked to three hydrogen atoms, called a methyl group, attaches itself to a stretch of DNA, thus “turning off” the expression of a gene. This biological “switch” which progressively inactivates the expression of a series of genes, determines cellular aging over time. This is a well-studied process also in human degenerative diseases and allows us to estimate, at the molecular level, the true biological age of an individual.
Starting from these premises, the researchers measured the degree of DNA methylation in the sample of 104 Labrador dogs and in 320 human individuals. By studying the trend of the cellular aging graph (DNA methylation) of dogs and humans, a model and a mathematical formula describing this relationship were obtained. Applying the formula Human age = 16 × ln(Dog age) + 31, we obtain, for example, that a 1 year old dog corresponds to a human age of 31 years and a 5 year old dog corresponds to a human age of 57 years.
The study also highlighted the fact that dog aging is not a constant process over time, but occurs in “leaps”; it is faster in the first years of life because the DNA methylation process is initially quite fast, then slows down in the adult and resumes in later phases in the elderly dog.
Because the old rule of “multiply by 7” is wrong
An old rule of thumb, probably dating back to the 1950s, tended to calculate canine age in human terms, multiplying the dog’s actual years by 7. According to this rule, a 3-year-old dog would correspond to a 21-year-old man. In reality the evaluation was completely approximate and derived from a sort of comparison between the average lifespan of a dog, which is around 10 years, and that of a man of the time, who lived on average 70 years. Today 8 should be used as a multiplier, given that the average human age has lengthened and reached around 80 years.
Recent scientific studies demonstrate that this type of comparison was completely wrong, considering that various factors contribute to defining the degree of aging of the dog: each one is different in size, genetics, state of health and lifestyle. The same calculations cannot then be applied to all breeds; some are longer-lived than others and, in many cases, the size of an adult dog is inversely proportional to its life expectancy, in fact large breeds are on average less long-lived than small breeds.
Factors that influence aging: race and lifestyle
In addition to the breed, certainly, lifestyle is crucial in the aging process of our pet. Although like us humans, there may also be a genetic predisposition to longevity for dogs, the type of diet, physical activity and various environmental factors contribute to shaping their state of health. Stress conditions, unbalanced diet and poor physical activity make the aging process faster. Especially elderly subjects, by changing their metabolism, should receive a diet that does not favor obesity or diabetes and should therefore avoid ultra-processed feed or feed with high fat content. Very often even “homemade” diets can be unbalanced in the composition of nutrients or even contain ingredients that are indigestible or toxic to the dog’s health. Exposure to pollutants present in the environment in which dogs usually live also affects their aging and state of health. In fact, recent research shows that our pets, both dogs and cats, are affected by the presence of environmental pollutants which, unfortunately, they share with humans.
