To study the link between dogs and longevity, researchers at Uppsala University in Sweden reviewed national registry records of Swedish men and women, ages 40 to 80. They focused on 3.4 million people who had no history of cardiovascular disease in 2001, and followed their health records—as well as whether they registered as a dog owner—for about 12 years. Dog ownership registries are mandatory in Sweden, and every visit to a hospital is recorded in a national database.

They found that dog owners had a lower risk of death due to cardiovascular disease than people who did not report owning a dog, as well as a lower risk of death from other causes. That was true even after adjusting for factors such as smoking, body mass index and socioeconomic status.