MONDAY, Oct. 16, 2023 (HealthDay News) -- For dogs, body size matters.

That’s true in terms of how quickly they age, but also in their mental health, according to a new study comparing big and little canines.

Age-related decline starts at 7 to 8 years of age in big dogs, compared to 10 to 11 years in smaller dogs, Hungarian researchers found.

But big dogs decline more slowly than their pint-sized peers. Large dogs maintain their mental health longer and have a smaller degree of age-related decline.

“For those who want a smaller-sized dog but do not want to risk severe mental health problems in old age or want a larger-sized dog but do not want to risk physical health problems at 7 to 8 years of age, we recommend a dog from the [22- to 66-pound] size range,” said first study author Borbála Turcsán, who is part of the Senior Family Dog Project at ELTE Eötvös Loránd University in Budapest, Hungary.

“Based on our results, these dogs have a longer health span relative to their expected life span than their smaller and larger counterparts,” Turcsan explained in a university news release.

Based on data from 15,000 dogs, giant dogs typically live to 7 years. Small dogs live to about age 14.

Purebreds tend to have shorter lives than mixed breeds.

The researchers investigated at what age behavioral and mental ("cognitive") changes start and how fast they progress. They also looked at dog body size, head shape and purebred status in relation to these age-related changes.

What they found is that behavioral and cognitive aging in dogs begins around 10-1/2 years of age, but when aging begins and how fast it progresses depends on the body size.

Dogs weighing more than about 66 pounds had earlier onset of age-related decline.

“Larger dogs experience a physical breakdown at an earlier age, and the accumulating illnesses, and degradation in sensory functions leads to ‘old-age behaviors’ long before their mental decline would begin,” Turcsán said.

Dogs weighing around 14 pounds had a four times higher rate of cognitive decline in old age than larger dogs.

Long-nosed dogs, including greyhounds, have a higher risk for mental decline in old age compared to dogs with other head shapes and mixed-breeds.

The study authors noted that dog owners start thinking of their dogs as old around age 6, regardless of size or purebred status.

"Owners consider their dogs 'old’ four to five years earlier than would be expected from behavioral data," said Enikő Kubinyi, head of the Senior Family Dog Project. "This may be due to graying and barely noticeable changes."

The study was recently published in the journal GeroScience.

More information

The American Kennel Club has more on aging in dogs.

SOURCE: Eötvös Loránd University, news release, Oct. 12, 2023