Study shows dog ageing defies seven-year rule

Dogs do not age at a steady pace like humans, challenging the familiar rule that their age should be multiplied by seven, according to a study reported by ERR.

US researchers found that puppies mature extremely rapidly at the cellular level during the first stages of life, while the rate of ageing slows later. An eight-week-old puppy is developmentally similar to a human infant of about nine months, when both begin growing their first teeth.

By its first birthday, however, a dog is biologically comparable to a 30-year-old human. Later, ageing slows: a 12-year-old Labrador is roughly equivalent to a 70-year-old person.

A new age formula

For decades, people have used a simplified calculation in which each year of a dog’s life equals seven human years. Physiologically, the theory has always been inaccurate. Unlike a seven-year-old child, a one-year-old dog is often already sexually mature.

To develop a more precise comparison, a team of US geneticists studied mammalian DNA. During an individual’s lifetime, chemical markers called methyl groups attach to strands of genetic material. These markers can switch genes on or off in response to environmental factors and age.

The pattern formed by the accumulation of these markers is known as an epigenetic clock. Researchers can use it to estimate an individual’s actual biological age.

The team analysed the genetic material of 104 Labrador retrievers ranging from several weeks old to 16 years old. They compared the dogs’ DNA methylation patterns with earlier data from 320 humans and 133 mice.

Based on the comparison, the researchers developed a logarithmic formula for converting dog years into human years. The formula is: human years equal 16 times the natural logarithm of the dog’s age, plus 31.

Under the new calculation, a one-year-old dog is biologically equivalent to a 31-year-old human. A two-year-old dog corresponds to a 42-year-old person, while a 10-year-old dog is roughly equivalent to a 68-year-old.

The rapid biological development of puppies points to a deeper genetic mechanism. Across all the species studied, the largest epigenetic changes occurred in specific regions of the genome, particularly in gene networks that guide anatomical development in the fetus.