"There is a lot of anecdotal evidence that people feel increased well-being with their dog; we wanted to investigate this," said Dr. Tove Fall, one of the authors of the study and professor of molecular epidemiology at Sweden's Uppsala University.
Heart attack survivors in the study who were living alone, but owned a dog, had a 33% lower risk of death, while stroke survivors who lived alone and had a dog had a 27% reduced risk of death, compared to people who did not own a dog and lived in a single household group.
"We found the dog owners had lower mortality than non-owners with the largest difference seen in the subgroup of people that lived in a single household," Fall said. "This group is especially vulnerable. It seems that dogs can alleviate the impact of living alone; they can increase social interaction."
Dr. Eugenia Gianos, system director of cardiovascular prevention at Northwell Health, added, "It is very likely that people who own pets have many other positive behaviors, including exercise, healthy eating and social connectivity, which are likely to be leading to better outcomes in health. However, it is also positive that emotional connection to a pet can have positive effects on various parameters that could improve outcomes for people."
The significant results were seen in people who live alone.
"Whether being single or married, it is about having positive social interaction that is associated with better health outcomes," Gianos said. "It could be that in a marriage, if you have challenges then you could have more stress that is related to high blood pressure and worse outcomes. With being single, it could be that the pet is providing companionship and preventing loneliness that is leading to improved benefit."
The study even compared several dog breeds to see if there were different cardiac outcomes.
"We found that many of the larger breeds and smaller breeds that are active such as terriers have better outcomes – survival outcomes," Fall said. "Those that did not show as much are the companion toy group and mixed breeds. The physical activity might be less."
However, she cautioned, "It is also a personal choice; you might choose a dog that fits your lifestyle. Part of the association might be seen by people who are more active getting a more active dog and have better cardiac outcomes."
"Dogs might be beneficial for human health, however, we do not know if unmeasured factors affect the results. In the national register, they do not measure behavior such as smoking or food intake. In this study we cannot account for smoking. The factor of smoking might play into this relationship when the cause was something else," Fall added.
Gianos agreed, saying, "Those two behaviors happen to be most linked with heart disease in research, which are extremely important to control. We would want to make sure that those two factors were not contributing to the improved outcomes that we are seeing."
Regardless of these shortcomings, the author maintained dogs are "a fantastic motivator."
Dr. Danielle Weitzer is a psychiatry resident and a member of the ABC News Medical Unit.