A study of 343 mentally and physically healthy adolescents in Tokyo found that teenagers who lived with a dog had lower scores for a range of social and behavioural problems compared with their peers; 96 of the young people in the sample kept a dog at home. Pet ownership, particularly of dogs, is associated with higher mental well-being in adolescents, including increased self-esteem and reduced loneliness.

The research, published in the journal iScience, suggests that differences in teenagers’ oral microbiomes may be one pathway linking dog ownership to improved mental-health measures. In laboratory follow-up, mice given microbes from dog-owning adolescents displayed more social behaviours, a result the authors present as supporting evidence for a microbiome-driven effect.

Researchers drew on data from the Tokyo Teenager Cohort Study, analysing standardised child behaviour checklists and oral microbiome samples from 343 participants. The study reported that dog owners had significantly lower scores for social problems and several other behavioural issues, including delinquent behaviour and aggression, compared with non-dog owners. Families can foster their dog’s positive impact on a teenager’s mental health by encouraging regular interaction and shared responsibilities, such as walking and playing, which enhance routine and a sense of competence.

The analysis found that overall diversity and richness of the oral microbiome did not differ markedly between groups, but composition did: certain bacterial taxa were more abundant in adolescents who kept dogs. Mice transplanted with microbes from dog-owning teenagers showed behavioural shifts in lab tests, including increased social sniffing and prosocial responses toward a trapped conspecific, the authors reported.

Prof Takefumi Kikusui of Azabu University, a lead author, framed the microbiome as a plausible mechanism linking dogs and adolescent wellbeing. “Several studies have reported the mental health benefits of dog ownership, and we have demonstrated that the microbiome may be one mechanism involved,” he said. He also noted that around 9–11% of Japanese households own a dog, a figure that is lower than in many other countries, reflecting cultural differences in pet ownership.

At the same time, Kikusui cautioned about cause and effect. “It remains unclear whether these differences [in microbes among dog owners] stemmed from the dogs themselves or whether owning dogs reduced stress, leading to the resulting changes in microbiota,” he said. Prof Stefan Reber of Ulm University likewise emphasised the observational limits of the human data: “It has only been shown that teens with dogs have a different salivary microbiome than teens without dogs.”

The paper describes mice experiments in which researchers transplanted microbiota from adolescents who kept dogs; those animals exhibited increased social behaviours in standard tests compared with mice that received microbes from non-dog owners. The authors interpret the results as consistent with microbe-driven effects on sociality, while noting that human data remain correlational.

Beyond behavioural scores and mouse tests, the study noted that some bacterial groups linked with prosociality and empathy were more prevalent in the microbiomes of adolescents who kept dogs. The authors also observed that, separately, dogs with many behavioural issues can impose stress on their owners. “It is known that dogs with many behavioural issues can impose stress on their owners,” Kikusui said.

The findings add to a growing body of work examining how close contact with animals can shape human microbial communities and, potentially, behaviour. Popular Science provided an accessible overview of the experiments and implications, and Theweek summarised the core results for a general audience.

The study was published in iScience and draws on the Tokyo Teenager Cohort Study sample. The authors underline that while laboratory follow-ups in mice supply mechanistic hints, the human associations reported are observational, and further work is needed to map causal pathways.

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Original reporting: view the original article.