It’s no surprise that dogs benefit people’s mental health. In a paper published in the Cell Press journal iScience, researchers point to a reason as to why: dogs prompt changes in the collection of microbes that live in and on our bodies, resulting in an increase in mental health.
“Raising dogs has beneficial effects, especially for adolescents, and these effects may be mediated through symbiosis with microorganisms,” says author Takefumi Kikusui of Azabu University in Japan.
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In previous work, Kikusui’s team found that young people who grow up with a dog from a young age and continue to have dogs later in life score higher on measures of companionship and social support. Other studies showed dog owners also have differences in their gut microbiomes, including greater microbial diversity.
Beneficial effects
In this study, the researchers set out to explore whether some of the beneficial effects of dogs on adolescent mental health might be tied to these differences in the microbiome.
“Adolescent children who keep dogs exhibit higher mental well-being, and we also found that dog ownership alters the gut microbiota,” said Kikusui. “Since the gut microbiota influences behavior through the gut-brain axis, we conducted this experiment.”
The researchers found that a person’s dog-owning status at age 13 predicted their mental health and behavioral scores. Social problems were significantly lower in adolescents with a dog at home compared to those without a dog.
Oral microbiome
Next, they looked at microbiome samples collected from the mouth. After sequencing the microbes, the researchers found similar species diversity and richness between the two groups of teens. But the microbiome composition showed differences, suggesting that owning a dog shifted the abundances of specific oral bacteria. They hypothesized that some of those bacteria might correlate with the adolescents’ psychological scores.
To put this idea to the test, the researchers treated laboratory mice with microbiota from dog-owning teens to see whether and how it affected their social behavior. Mice with the dog-owning microbiome spent more time sniffing their cage mates. The animals also showed a more social approach toward a trapped cage-mate—a behavior test standardly used to test prosocial behavior in mice.
Bacteria promoting empathy
“The most interesting finding from this study is that bacteria promoting prosociality, or empathy, were discovered in the microbiomes of adolescent children who keep dogs,” Kikusui said. “The implication is that the benefits of dog ownership include providing a sense of security through interaction, but I believe it also holds value in its potential to alter the symbiotic microbial community.”
The researchers say that while more research is needed, the results suggest that a family dog can change the microbiome in ways that support mental health, empathy, and prosocial behavior. The benefits of living with dogs are likely the result of tens of thousands of years of human-canine coexistence, they say.
This work was supported by funding from the JST-Mirai Program.
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