Dogs May Be Making Teens More Empathetic Through Their Bacteria 

In this article:

• What did researchers discover about dog kisses and the teenage gut?
• Drilling down on causation through empathetic mice
• Why did the researchers focus on teenagers?
• Should I get a dog for my teenager?

The relationship between humans and their canine companions isn’t just skin deep. It is, according to one scientific paper recently published in iScience, potentially gut deep.

Researchers from Azabu University in Japan found that household dogs may have an impact on teenagers’ mental health—not only because of the cuddles or the responsibility of caring for another living thing, but also due to dogs’ influence on the makeup of teens’ microbiomes.

Dog kisses appear to improve teenagers’ gut microbiomes and mental health

The researchers hypothesized that adolescents raised alongside dogs develop distinct microbial populations, and that this distinction can correlate with improved psychological well-being and increased capacity for prosocial behavior. The microbiome—composed of the trillions of organisms that live inside and on us—has become a central area for research this century because of its influence on bodily functions like metabolism and immunity, as well as mental health, personalities, and moods. But dogs’ possible effect on the human microbiome is a fairly new addition to the list of reasons that pet ownership might be a boon to mental health.

Takefumi Kikusui, a professor who led the investigation, set out to test whether humans’ microbiomes and behavior changed when they lived with dogs during these formative years. His research group had previously documented that young people who maintained continuous contact with dogs from childhood through adolescence reported stronger emotional bonds and social support networks.

The study monitored 345 young people beginning at 13 years old, examining psychological measures and microbial composition over time. Subjects living with dogs demonstrated better mental health metrics, particularly showing reduced difficulties in social interactions compared with their peers in dog-free households.

The research team collected oral microbiome samples to investigate whether bacterial communities might help explain these mental-health differences. Their analysis revealed a difference in the microbiomes of participants with and without dogs: While the overall variety of microbes remained comparable across both groups, the specific types of bacteria present varied significantly. Dog-owning teens had elevated levels of certain bacterial species.

Gerard Clarke, PhD, who studies the way the gut microbiome influences brain function and behavior as a professor of Neurobehavioral Science at University College Cork, notes that while there has been interest in using the oral microbiome as an early warning system for neuropsychiatric disorders, “this is an area that still requires further evaluation.” He explains that our understanding of how oral bacteria might affect brain health is “less well defined than our knowledge” of the gut-brain axis.

Still, while samples directly from the gut or fecal samples are more reliable, there is a relationship between the bacteria in the gut and the bacteria in the mouth, which the researchers in this study settled for, since collecting fecal samples from participants would be, in very unscientific terms, a whole thing.

Saliva from dog-owning teens appeared to make mice more empathetic, too 

To establish causation, the researchers conducted controlled laboratory experiments using mice. When the animals received oral microbial transplants from dog-owning teenagers, their behavior shifted. These mice spent increased time investigating their companions. 

Most notably, in experiments designed to measure cooperative behavior, the animals’ responses appeared more prosocial. In one experiment, some mice were put in tubes and others were outside of them. Mice that received transplants from dog owners’ microbiomes chewed through the tubes, sniffed, and poked their noses in significantly more than those with non-dog-owning transplants. This test is supposed to measure a kind of empathetic behavior in mice.

Dr. Clarke welcomes the researchers’ attempt to move beyond correlation toward causation, though he noted that fecal microbial transplantation has been “the gold standard” for establishing causality in microbiome-gut-brain research. (As opposed to the oral administration. The study also lists this as a limitation.) He pointed out another issue too: “Oral and gut microbes thrive in very different ecosystems,” he said. “While this study gives encouraging initial proof-of-principle evidence, I’m not sure how plausible it is that oral microbes would translocate to such an extent that they would dominate the gut environment under physiological conditions.”

Why study teenagers and dogs?

The research team deliberately focused on the teenage years, a period when changes in mental health, like the appearance of depression and social anxiety, are often noticed. Dr. Clarke considers this focus particularly valuable, calling adolescence “a very turbulent time of life with many important life-stage transitions that we need to know more about, especially given most mental health conditions first emerge during this time window.”

However, Dr. Kikusui believes these microbial effects likely extend beyond the age group he studied. His team has initiated new research examining microbiome-wellness connections in elderly populations.

So… should I get a dog for my teen?

As promising as these findings are, Dr. Kikusui told Digest in an email that everyone with a teen shouldn’t feel they have to run out and get a dog. “My goal isn’t necessarily to promote dog ownership,” he said. “Rather, I hope people recognize the value of natural environments—including animals and their associated microbiomes—for humans increasingly surrounded by artificial environments.”

Dr. Clarke echoed this focus on environmental impacts, noting that “it is not really clear from this study what is driving the changes in the microbiota in dog-owning adolescents.” Multiple factors could be at play, he suggests, including wider social networks, increased access to green spaces, and more physical activity. “It’s not just about how we interact with dogs as our best friends—there are many benefits to dog ownership.”

Dr. Kikusui has worked on and published several studies in his career that examine the relationship between canines and humans. As he suggested to us, it’s a fruitful avenue of study that speaks to the larger arc of humanity—no small thing.

“Cooperative societies enabled human advancement and achievement,” he said. “Dogs represent arguably the only animal species to become so extensively and intimately integrated into these cooperative structures. Studying human-dog relationships illuminates both human social characteristics and dogs’ unique qualities, ultimately revealing insights about contemporary society, cooperation, and reciprocal relationships.”