Research suggests that having a dog in the home may help improve the mental health of teenagers, with scientists adding that this may be partly due to the sharing of germs.
Professor Takefumi Kikusui from Azabu University in Japan, who led the work, said interacting with dogs can reduce owner stress and stimulate the release of the binding hormone oxytocin.
But research suggests there may be other reasons why dogs can have a positive impact.
“Several studies have reported the mental health benefits of dog ownership, and we demonstrated that the microbiome may be one of the mechanisms involved,” Kikusui said.
Publication in iScience magazineKikusui and his colleagues describe how they analyzed the results of a survey of 343 mentally and physically healthy adolescents who took part in the study. Tokyo Adolescent Cohort Studyof which 96 were dog owners.
The team found that adolescents who had dogs at age 13 had significantly lower scores on social problems, social isolation, thinking problems, delinquency and aggressive behavior by age 14 than those who did not own dogs.
The researchers then analyzed the microbes found in the teenagers' saliva and found that while there were many similarities between them, 12 types of bacteria, including Streptococcus and Prevotella, were significantly less common in the saliva of non-dog owners.
The team transplanted microbes from the teenagers' saliva into mice that had no germs of their own. The results showed that mice with germs from dog-owning teenagers were more likely to sniff unfamiliar mice and approach trapped cage mates.
“This [latter] the behavior is called “bias” or “empathic concern,” which is a kind of empathic response in humans and animals,” Kikusui said.
The team added that the abundance of certain bacteria in the guts of mice is associated with differences in their social behavior, with some of these strains also associated with adolescent behavior.
“Although it is not possible to directly compare human and mouse behavior, these results suggest that microbiota are partly responsible for adolescents' improved social behavior after living with dogs,” the team wrote.
However, the team did not analyze the microbes carried by the participants' dogs, with Kikusui noting that “it remains unclear whether these differences are [in microbes among dog owners] was due to the dogs themselves or because dog ownership reduced stress, leading to corresponding changes in the microbiota,” he said.
Professor Stefan Reber from the University of Ulm, who was not involved in the work, agreed. “It has just been shown that teenagers with dogs have a different salivary microbiome than teenagers without dogs,” he said.
In addition, how microbes may influence behavior remains to be determined.
Kikusui added that the study doesn't mean everyone needs a canine companion. “Even without a dog, maintaining a diverse microbiome has the potential to improve mental health outcomes,” he said.
Indeed, for some, owning a dog can be a negative experience. “Dogs with many behavioral problems are known to cause stress to their owners,” Kikusui said.
