Japanese scientists from Azabu University and Gunma University have published the results of a study analyzing data from 343 13-year-olds involved in the Tokyo Teen Cohort project. The study divided participants into two groups: 96 teenagers living with dogs and 247 without pets. Those living with a dog showed significantly higher mental health indicators than their peers without a pet. Led by researchers Eiji Miyachi and Takefumi Kikusui, the work links this effect to changes in the adolescents' gut and salivary microbiomes.
Adolescents with a family dog showed statistically significant lower levels of anxiety and were less likely to display aggression or social withdrawal. Analysis revealed that the most pronounced impact occurred within the category of social problems. These teens were more likely to harbor bacteria associated with empathy and prosocial behavior. Scientists found that microbes of the genus Streptococcus play a key role; when these bacteria were transplanted into laboratory mice, the rodents began to behave more socially, interacting more with each other. The researchers noted that bonding with a dog does more than just lower stress; it also influences the composition of the microbial community within the teenager's body.
According to the scientists, the underlying mechanism involves the direct transmission of microbes from dog to human through shared living spaces. The canine microbiome influences the bacterial composition of the teenager's gut and oral cavity, which in turn affects mood and behavior via the "gut-brain axis." Researchers suggest that the microbiota impacts the production of neurotransmitters and other bioactive substances that drive social behavior. Analysis of saliva samples confirmed differences in microbial profiles between the groups with and without dogs: although species diversity was comparable, the community composition differed significantly.
For families, this translates to a tangible benefit: having a dog at home can serve as a natural mental health support factor during the critical stage of adolescence. The effect is particularly pronounced among those who actively care for their pet and spend time on walks—the study confirms that the time invested in a relationship with a pet yields measurable results.
This research adds to the expanding evidence of the positive human-animal bond and provides the first experimental proof that the microbiome is a critical biological mediator in this relationship. The work was published in December 2025 in the journal iScience and was supported by Japanese national scientific programs. Scientists plan to continue their observations to determine how lasting this effect is over time and how it might vary based on socioeconomic factors and other variables affecting the microbiome.
