New research shows that owners of a dog with diabetes were more likely to develop type 2 diabetes during follow-up than owners of a dog without diabetes.

The International Diabetes Foundation estimates that 9.3% of adults worldwide are living with some form of diabetes—more than 460 million people, and type 2 is the most common kind. That number is expected to grow in the coming decades, due in part to an aging global population and ongoing shifts in lifestyle behaviors, especially those that contribute to a rise in obesity rates.

Researchers at Uppsala University in Sweden compared data from 208,980 owner-dog pairs (175,214 owners and 132,783 dogs) and 123,566 owner-cat pairs (89,944 owners and 84,143 cats) obtained from veterinary care insurance data during a baseline assessment period from January 1, 2004, to December 31, 2006. Owners with type 2 diabetes were identified through information obtained from Swedish national health. The researchers discovered that owning a dog with diabetes was associated with a 38% increased risk of having type 2 diabetes compared with owning a dog without diabetes.

Previous studies have suggested a link between obesity in dog owners and their pets, but the authors of the new study say theirs is the first to investigate the shared diabetes risk in dog and cat owners and their pets.

NEWStat asked corresponding author Beatrice Kennedy, MD, PhD, if she and her colleagues had any theories as to why this correlation exists.

“Previous studies have indicated a shared risk of adiposity in dogs and their owners,” said Kennedy, a postdoctoral researcher at Sweden’s Uppsala University. “Although we did not have access to information on household health behaviors, we believe that shared physical activity levels, dietary patterns, and shared risk of obesity might help explain our findings.” She said it’s also possible that other shared environmental exposures such as pollution or diabetogenic agents could play a role.

Kennedy told NEWStat that the study found no shared risk of diabetes between cats and their owners.

“This was somewhat surprising, as feline diabetes is usually considered more similar to [human] type 2 diabetes than canine diabetes,” she said. She speculates that the shared risk for dogs and humans might be due to their shared exercise patterns, something she says doesn’t really apply to cats and humans: “Cats are usually not as happy [as dogs] to partake in walks or shared physical activities.”

The study found that dog owners with type 2 diabetes shared some similarities: “[They] were older, more often men, and less likely to have a university-level education or to be married or cohabitating than the owners without type 2 diabetes.”

Kennedy said the diabetic dogs in the study also shared some similarities: “They were older, more often female, and more often belonged to breeds with a high risk of diabetes than the nondiabetic dogs.”

The researchers noted the high incidence of diabetes in breeds such as Australian terriers, Swedish lapphunds, and Samoyeds—breeds that Kennedy said are known to have high diabetes risks. “We did not analyze shared diabetes risk per breed group, as that would have resulted in very many very small groups of owner-dog pairs. We did, however, include overall breed diabetes risk in our analyses—and this did not decrease the elevated risk of type 2 diabetes in owners of a dog with diabetes.”

How should veterinarians and pet owners consider these findings? Kennedy said, “If a person (or dog!) is diagnosed with type 2 diabetes, that might be a good time to really re-evaluate the health behaviors of everyone in that home.

For more information on pets and diabetes, read the 2018 AAHA Diabetes Management Guidelines for Dogs and Cats.