A number of studies have in fact found that pets have positive effects.
"The dominant research approach for decades was only socio-psychological and examined certain effects of pets on their owners," said Detlev Nolte, general secretary of the Bremen-based research group Pets in Society.
The conclusions were based mainly on surveys and observations, so the findings were not very robust. Gradually, however, scientifically based research approaches have been developed as well, he said.
Ample evidence is now available that pets benefit their owners in many ways. There are physical benefits, for example, one of which is rather obvious but important nonetheless: exercise.
"According to a study by US scientists, 150 minutes of exercise weekly is enough to have a positive effect on the cardiovascular system," noted Ralf Jordan, chief physician at the Cardiac Rehabilitation and Prevention Clinic in Duisburg, Germany.
Dog owners are more likely to reach this number than the dogless.
Studies also show that people who are physically active outdoors daily have a stronger immune system.
"A dog forces you to go outdoors regularly," remarked Udo Kopernik, spokesman for the German Kennel Club. "People who own or look after a horse have to leave their home often, too."
You don't have to step outside to enjoy the health benefits of pets, though.
"It's been proven that the mere presence of animals, and above all petting them, greatly helps to lower blood pressure and heart rate," Jordan said.
The sympathetic nervous system is less active, he said, so the body releases fewer stress hormones such as adrenaline. This applies less to goldfish than to dogs, cats and other domesticised animals.
"A number of scientists have also found that physical activity has a beneficial effect on chronic illnesses like diabetes, cancer, hypertension and chronic bronchitis," Jordan said.
Having a pet can promote physical activity, he pointed out, thereby helping to keep such illnesses subdued and reducing the number and intensity of attacks, as in the case of bronchitis.
Pets can be psychologically beneficial, too. Various studies have shown that a person who lives alone, but has a pet, not only feels less lonely but also makes friends more easily. "Pets can serve to break the ice and make social contacts easier," Nolte said.