NEW YORK(NYTIMES) - Around the time Dante turned eight, he started to seem a little off. The 70-pound Bernese mountain dog would pace his family's home in Interlaken, New York, like a caged bear. Then he might stand stock still, staring trance-like at the pedals of the family's organ. Or at a corner of a room. In the middle of the night, he would wake up and begin barking incessantly, for no obvious reason.

Then the indoor incontinence began.

A brain scan confirmed that Dante had canine cognitive dysfunction, colloquially known as doggy dementia. It is often described as the dog's analog to Alzheimer's disease. Some studies have found it can occur in at least 14 per cent to 35 per cent of older dogs. But because the symptoms resemble those in other diseases, its true prevalence is difficult to confirm.

A large new study of 15,019 dogs enrolled in the Dog Ageing Project, an ongoing investigation into canine illness and ageing, published on Thursday (Aug 25) in the journal Scientific Reports, identifies the top factors associated with a dog's risk of getting the disease.

A key finding: Exercise may play a significant preventive role. The odds of a cognitive dysfunction diagnosis were 6.47 times higher in dogs reported as not active compared with those reported to be very active, researchers at the University of Washington found.

But they also said that the disease itself could lead to lack of exercise, emphasising that the study results, which are based on observations by owners, suggest correlation, not causation.

Odds of getting the disease also appear to increase in dogs that have neurological disorders, or impaired hearing or sight. Annette Fitzpatrick, a co-author of the study and a University of Washington research professor with expertise in dementia in people as well as canines, commented: "When you don't get stimulation from the outside world, it seems to increase the risk of our not even being able to use our brains as well."

The study, she said, "shows that there may be other things we can be aware of, to try to reduce the onset of cognitive dysfunction."

And certainly age matters. A dog's life expectancy often depends on breed, size and body mass: think mastiff (six to 12 years) versus Chihuahua (12 to 20 years). During the later years of a dog's projected life span, each successive year contributed to the potential for disease onset, the study found.

In fact, the researchers noted, risk factors that correlate with canine cognitive dysfunction mirror some of the factors for humans with dementia, including Alzheimer's disease.

Earlier studies of canine cognitive dysfunction often drew from veterinary assessments in smaller populations of older dogs; this one is culled from dogs who range in age from puppyhood to mid-20s. In the coming years, as these dogs grow older, the project, which has enrolled more than 40,000 dogs and hopes to reach 100,000, will issue more complex findings on cognitive dysfunction and other diseases.

In this study, the prevalence of canine cognitive dysfunction among all the dogs, young and old, was 1.4 per cent. But the average age of the dogs was just 6.9 years, and only 19.5 per cent of the dogs analysed were in the last quarter of their life span.

"This study compares dogs with cognitive dysfunction to those that don't have it," Prof Fitzpatrick said. "But as the years progress, we can look at the same dog who maybe had great cognitive function but then declined."

The results were derived from just one baseline accounting by owners of their dog's health and lifestyle experience between 2019 and 2020, and a particularly high-threshold cognitive function questionnaire.

Among the questions: - How often does your dog pace up and down, walk in circles and/or wander with no direction or purpose?

- How often does your dog get stuck behind objects and is unable to get around?

- How often does your dog walk into walls or doors?

- How often does your dog have difficulty finding food dropped on the floor?

If the study findings have a familiar, even intuitive ring, that may be because the Dog Ageing Project, which receives funding from the National Institute on Ageing, a branch of the federal National Institutes of Health, may shed insight into factors that affect the life span of humans well as the dogs who share their homes.

Unlike laboratory animal subjects such as fruit flies and mice, companion dogs are affected by their owners' environmental and social factors, such as secondhand cigarette smoke, lawn pesticides and access to health care.

"Estimates of human longevity say that about 75% is due to environment and 25 per cent is genetic," said Matt Kaeberlein, a biogerontologist at the University of Washington who is a co-director of the Dog Ageing Project. "So companion dogs give us the opportunity to really understand the role of that environmental variability in the biological ageing process."

Moreover, because dogs age much more rapidly than humans, the studies underway within the project provide opportunities along an expedited timeline for insights into human and canine ageing.

Canine cognitive dysfunction is difficult to pinpoint. A dog's seeming ignorance of a commonplace command could indicate deafness or old-age stubbornness rather than an atrophying brain. Symptoms that look like cognitive dysfunction could actually be from stroke, brain inflammation, diabetes or Cushing's disease, said Dr Nicole Ehrhart, a veterinarian and director of the Columbine Health Systems Centre for Healthy Aging at Colorado State University.

Veterinarians rely initially on keen owner observation, she said, and then perform diagnostic tests.

"Look at your dog looking into your eyes and see how long they hold your gaze, especially if you have a treat by your face," she said. "Because as dogs get dementia, they can't focus on things they would normally focus on."

Dr Ehrhart, who was not involved in the Dog Ageing Project study, called the new research "wonderful confirmation of something that we know across all species: that exercise is good for healthy ageing and that lifelong habits of exercise can be preventive for Alzheimer's disease and other cognitive issues."