Throughout those years, doctors regularly monitored changes in the cognitive health of these residents.
The team has just published the results of a large-scale study on the benefits of owning a dog.
The sample included roughly as many men as women, from different social backgrounds.
This follow-up focused in particular on the onset of forms of dementia and Alzheimer-type diseases.
At the end of this observation, the researchers found a risk of dementia twice as low among people living with a dog.
They explain that simply owning a dog produces numerous positive effects on physical and cognitive health.
Taking the animal out once or twice a day requires some walking, and therefore regular physical activity.
These walks also increase interactions with other people, on the street or in the park.
Even at home, the dog constantly engages the cognitive functions of the person who looks after it.
The results thus show that caring for a dog is a genuine exercise for the brain.
Fewer patients means fewer medical treatments, more people who can continue to live at home, and less care in hospitals or specialized facilities.
The Japanese team sought to measure the potential savings for the state.
According to this estimate, raising the rate of dog ownership among seniors to 13% would save, in patient care, more than 150 billion yen a year, or 850 million euros, or more than 4 billion over five years.