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CU Boulder researchers, with an international team of colleagues, find that childhood pets are linked to healthier stress responses

If you grew up in a city and without a pet, your immune system likely developed differently than that of someone who shared their childhood with a dog or cat. That difference, new research from �������� Professor Christopher Lowry suggests, could influence how your body responds to stress even decades later.

In in the journal Brain, Behavior, and Immunity, an international team of researchers, including Lowry and CU Boulder PhD student John Sterrett, found that for people raised in urban environments, having regular contact with pets early in life may protect against harmful immune responses to stress.

CU Boulder scientist Christopher Lowry and his research colleagues found that having regular contact with pets early in life may protect against harmful immune responses to stress.

“Being raised in a home with pets can provide protection against chronic low-grade inflammation, which we know is a risk factor for stress-related psychiatric disorders and more,” Lowry says.

The study adds to a growing body of evidence that our childhood environments can leave a lasting mark on our physical and mental health.

Our oldest friends

Lowry is a professor in the Department of Integrative Physiology at CU Boulder and has spent much of his career studying how the microbial world interacts with the human brain. It’s a fascination that traces back to the 1990s when he started exploring how soil microbes influence mood.

“For about 25 years, we have been interested in understanding how microbes found in our environment—in nature, soil, fermenting vegetable matter, and unpurified water—can signal from the body to the brain,” Lowry says.

Along with a research team directed by Stafford Lightman at the University of Bristol’s University Research Center for Neuroendocrinology, Lowry studied Mycobacterium vaccae NCTC 11659 (M. vaccae), a microbe commonly found in soil.

His lab found that exposure to M. vaccae in mice activated serotonin pathways in the brain and produced antidepressant-like behavioral effects.

“M. vaccae is representative of diverse microbes in nature that have the ability to promote immunoregulation and protect us from inappropriate inflammation,” Lowry explains.

The microbe soon became a model for studying what scientists now call “Old Friends”—the microorganisms humans co-evolved with and depend on for proper immune system development.

“Being raised in a home with pets can provide protection against chronic low-grade inflammation, which we know is a risk factor for stress-related psychiatric disorders and more,” says CU Boulder researcher Christopher Lowry. (Photo: Bonnie Kittle/Unsplash)

It’s thought that modern urban living, with its clean indoor environments and reduced contact with naturally occurring microbes, disrupts this relationship. In turn, people living in such environments have experienced a rise in chronic, stress-related disorders.

Pets as microbial messengers

In a previous study, Lowry and his colleagues that people raised on farms, with regular exposure to animals, exhibited lower inflammatory responses to psychological stress. But in that study, it was hard to separate the effects of rural living from contact with animals.

So, the team designed a new study to answer a more specific question.

“We designed the study to determine if having pets in the home could protect against inappropriate inflammation in individuals raised in urban settings,” Lowry says.

The team recruited healthy adult men who had been raised in cities either with or without household pets. The participants were then exposed to the Trier Social Stress Test, and measurements of their immune function and inflammation were taken both before and after completing stressful tasks like public speaking.

Compared to their pet-free peers, individuals who grew up with pets showed a more balanced immune response and better regulation of stress-reactive cells.

But what accounts for this striking result?

“Exposures to ‘Old Friends,’ which are thought to increase in homes with pets, interacts with our immune system to produce more regulatory T cells,” Lowry explains. “Without sufficient exposure to ‘Old Friends’ we have reduced capacity to produce these regulatory T cells, which leads to inappropriate or unresolved inflammation.”

In short, a four-legged friend in the house means more microbial diversity. That might be just what your immune system needs to stay in balance.

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Something as simple as living with a pet could help buffer the long-term health risks of urban living, notes CU Boulder researcher Christopher Lowry. (Photo: Helena Jankovičová Kováčová/Pexels)

From theory to therapy

Lowry and his team’s findings are just the beginning. He is now involved in several projects exploring how they could be applied in the real world.

“We are interested in exploring if we can increase mental health outcomes by increasing exposure to ‘Old Friends,’” he says, pointing to clinical trials testing microbial supplements and high-diversity plant-based beverages, which contain diverse microbial communities.

He’s also a co-founder of a CU Boulder startup company Kioga, which is developing soil-derived microbiome-based nutritional supplements, food ingredients and therapeutics. Their goal is to improve mental health outcomes for anyone experiencing high levels of perceived stress, whether or not they have a diagnosed disorder.

What comes next?

Lowry also notes that more research is needed to explore if the recent findings hold true for women or people of different ages or backgrounds.

“This is an extremely important question,” Lowry says. “More work is needed to fully understand the importance of upbringing in rural versus urban lifestyles in females.”

Still, the implications are clear. Something as simple as living with a pet could help buffer the long-term health risks of urban living. Given that more people than ever today live in cities and stress-related conditions are on the rise, Lowry’s work offers a hopeful solution.

“Humans co-evolved with these microbes in nature, and our body depends on them for a normally functioning immune system,” he says.

So, the next time you’re scrubbing muddy paw prints off the floor, remember that your four-legged friend is just trying to help you stay healthier in the long run.��

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