Growing Up With a Dog Might Lower Crohn’s Risk

Results from a study presented at Digestive Disease Week (DDW) 2022 in San Diego highlighted a possible link between living with a dog as a child and protection against developing Crohn’s disease later in life.

While the study has yet to be peer-reviewed or published, the researchers hope that their discovery could help find ways to prevent inflammatory bowel disease (IBD) in high-risk children.

What Did the Study Look At?

The environmental questionnaire study is part of the larger Crohn’s and Colitis Canada Genetic, Environmental, and Microbial Project’s goal to identify genetic, environmental, and microbial determinants of Crohn’s disease.

The study surveyed over 4,200 healthy, first-degree relatives of people diagnosed with Crohn’s disease. They were asked 67 lifestyle questions, which included their pet history.

What the Results Showed

The researchers looked at stool samples from everyone in the study. They found that people who lived with dogs from ages 5 to 15 had signs of a healthy balance of gut microbes and less gut permeability in their stool, which are important protectants against developing Crohn’s disease.

“Half the people who lived with dogs ended up being protected against Crohn’s disease,” Williams Turpin, PhD, the study’s senior author and a research associate with Mount Sinai Hospital and the University of Toronto, told Verywell. “This could be a potential tool to reduce the risk for Crohn’s and improve long-term outcomes.”

What is Crohn’s Disease?

Crohn’s disease is a type of chronic inflammatory bowel disease (IBD). It can affect all parts of the gastrointestinal tract (GI) from the mouth to the anus.

Crohn’s causes long-lasting inflammation in the GI tract that might be driven by an overactive immune response that targets normal healthy gut bacteria. The inflammation leads to the many symptoms of a Crohn’s “flare,” including:

• Rectal bleeding
• Continuous diarrhea 
• Abdominal cramps and pain
• Constipation 
• Feeling like you need to move your bowels
• Loss of appetite
• Weight loss
• Low energy and fatigue 
• Delayed child growth and development
• Symptoms outside the GI tract like kidney stones, low bone density, skin disorders, joint pain, and fevers

People with Crohn’s may not always have symptoms; sometimes, the disease goes through periods of remission. There are also treatments that can help manage Crohn’s.

Who Gets Crohn’s?

Inflammatory bowel disease, which includes Crohn’s and ulcerative colitis, affects over 3 million Americans.

It tends to run in families: about 20% of people with Crohn’s disease have a first-degree relative (e.g., parent, child, sibling) with IBD. While Crohn’s disease can develop at any age, it is most common in adolescents and adults between the ages of 15 and 35.

We don’t know exactly why some people develop Crohn’s, but it’s likely a combination of risk factors, such as:

• Having parents diagnosed with IBD
• Being of European ancestry
• Living in an urban city or town
• Living in northern climates 
• Smoking

Why Would Living With a Dog Protect Against IBD?

In addition to providing answers to the environmental risk assessment, the study participants—who lived in different parts of the world—also gave urine, blood, and fecal samples that measured their microbiomes, levels of subclinical inflammation, and gut barrier function.

The participants who said that they lived with a dog when they were between the ages of 5 and 15 had positive biomarkers that are known to provide protection against IBD, including:

• Lower levels of fecal calprotectin (associated with intestinal inflammation)
• Improved barrier function (the lining that keeps bacteria inside the intestines)
• An altered microbiome (which may help protect against inflammation)

The “Hygiene Hypothesis”

Turpin said that one reason why dogs might help protect against intestinal inflammation is that our canine companions share their skin microbiome with us. Although research is limited, studies have shown that pets can significantly alter the skin and gut microbiomes of their owners.

Another environmental factor that may offer protection for dog owners is the likelihood that they spend a fair amount of time outside, compared to people who have other household pets like cats that don’t need to be walked.

That theory lines up with the hygiene hypothesis—the idea that multiple childhood exposures to pathogens may help protect an individual from developing IBD later in life.

What About Other Pets—and People?

In addition to the discovery that dog ownership may provide protection against Crohn’s, the study also revealed some other interesting data that shed light on who is at high risk for developing the disease.

The researchers didn’t observe the same findings in the stool samples from people who grew up without a dog, or who had other pets like cats.

In fact, people who were currently living with a bird were more likely to develop Crohn’s in the future, as they were found to have elevated fecal calprotectin levels—a biomarker associated with intestinal inflammation and symptoms of the disease.

The researchers also found that the other humans a person grew up with might also affect their Crohn’s risk. For the people who had a first-degree relative with Crohn’s, living with a larger family—three or more people—was associated with more protection against developing the disease.

The researchers think this finding could also be associated with the hygiene hypothesis, as children from large families may have greater exposure to viruses, bacteria, and parasites, which in turn may help them build a robust immune system that can protect them throughout adulthood.