Dog owners have a lower risk of dying early, according to a new study.
Researchers at Sweden's Uppsala University tracked more than 3.4 million people with no heart disease over a 12-year period, adjusting the data for relevant factors like age and gender.
They discovered those who owned dogs had a 20 percent lower risk of premature death than those who didn't. Dog owners were significantly less likely to develop cardiovascular disease, particularly if they owned a breed traditionally associated with hunting such as terriers, retrievers and scent hounds.
The study's most significant findings were the health benefits for those who live alone. In single-person households with dogs, the risk of dying from cardiovascular disease was 36 percent lower than those without. Single dog owners also had an 11 percent reduction in their risk of heart attacks. People who live alone have previously been shown to be at higher risk of death from cardiovascular disease.
There are several possible explanations as to why dogs seem to help humans live longer. One is that dogs need to be walked every day, increasing the physical activity of their owners. However, researchers are hesitant to say owning a dog increases exercise levels, as the people who choose to buy or adopt dogs - particularly hunting breeds - are likely to be fairly active already.
Another reason is that owning a dog may protect people from disease by exposing them to bacteria they may not have encountered otherwise, which would increase their immunity.
Dog ownership also tends to increase a person's social contact with others, which may improve their overall wellbeing.
Dr Mike Knapton of the British Heart Foundation told the BBC previous studies had suggested the association between dog ownership and cardiovascular health, but had not been as conclusive as this massive Swedish study.
"Dog ownership has many benefits, and we may now be able to count better heart health as one of them," he said.