Dogs shower their owners with affection and demand walks on a regular basis. And according to medical researchers, a corresponding link between dog ownership and heart health — previously called "probable" by experts — is supported by Swedish data.

An examination of Sweden's national records — spanning more than 3.4 million people and 12 years — found that registered dog owners had a lower rate of cardiovascular disease and a lower risk of death.

The research was published in Nature's Scientific Reports on Friday.

Several years ago, the American Heart Association concluded that pet ownership, "particularly dog ownership," is "probably" associated with a reduced risk of cardiovascular disease. But they noted the "scant data" on pet ownership and human heart health in large general populations.

The researchers in Sweden set out to "clarify the association" between dog ownership and heart health. Unlike previous researchers, they had access to hospital visit data for millions of Swedish citizens, thanks to the public health care system — plus two large databases of dog owners, because dog registration is mandatory in Sweden.

Comparing the records, they found a reduced risk of heart attack, death from cardiovascular disease, and death from any cause among registered dog owners. The trend remained even when controlled for age, sex, education and socioeconomic status, among other factors.

The researchers note that previous research in Norway and the U.S., working with much smaller pools of data, didn't find a connection between dog ownership and heart health. They suggest that the smaller sample sizes explain the lack of results.

They also acknowledge it's possible that there are other explanations for the link, like some unknown factor that affects both the choice to own a dog and other lifestyle decisions. And the data are not perfect — while dog registration is mandatory, for instance, not all dog owners comply.

But overall, the researchers say the large Swedish data set provides "the most robust evidence so far of a link between dog ownership and health outcomes."

"Dog ownership was especially prominent as a protective factor in persons living alone," lead author Mwenya Mubanga said in a statement released by Uppsala University. "The results showed that single dog owners had a 33% reduction in risk of death and 11% reduction in risk of myocardial infarction [heart attack] during follow-up compared to single non-owners."

Hunting breeds, like terriers and retrievers, had a particularly strong association with a lower risk of cardiovascular disease.

As NPR's Allison Aubrey has reported, a study earlier this year found that dog owners get more exercise than non-dog owners — 22 more minutes of moderate-pace walking a day, on average:

"The study found that the dog owners walked briskly and got their heart rates up. At times, their pace was about 3 miles per hour, which the Centers for Disease Control and Prevention considers moderate intensity.

"Prior studies have shown that moderate-intensity walking is just as effective as running in lowering the risk of high blood pressure, high cholesterol, Type 2 diabetes and other conditions. And the more people walk, the more the health benefits increase, according to the American Heart Association. ...

"As dog owners know, when your hound leaps up onto your bed in the morning, you have little choice but to get up and go."

The companionship provided by a dog could also have positive effects on health, Allison reported.

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