Family Size, Dog Ownership May Lower Risk of Crohn’s Disease

People who live with at least two other people in their first year of life and have a dog during childhood may be at reduced risk of developing Crohn’s disease (CD), according to investigators.

Those who live with a pet bird may be more likely to develop CD, although few participants in the study lived with birds, requiring a cautious interpretation of this latter finding, lead author Mingyue Xue, PhD, of Mount Sinai Hospital, Toronto, Ontario, Canada, and colleagues reported.

“Environmental factors, such as smoking, large families, urban environments, and exposure to pets, have been shown to be associated with the risk of CD development,” the investigators wrote in Clinical Gastroenterology and Hepatology. “However, most of these studies were based on a retrospective study design, which makes it challenging to understand when and how environmental factors trigger the biological changes that lead to disease.”

The present study prospectively followed 4289 asymptomatic first-degree relatives (FDRs) of patients with CD. Environmental factors were identified via regression models that also considered biological factors, including gut inflammation via fecal calprotectin (FCP) levels, altered intestinal permeability measured by urinary fractional excretion of lactulose to mannitol ratio (LMR), and fecal microbiome composition through 16S rRNA sequencing.

After a median follow-up period of 5.62 years, 86 FDRs (1.9%) developed CD.

Living in a household of at least three people in the first year of life was associated with a 57% reduced risk of CD development (hazard ratio [HR], 0.43; P = .019). Similarly, living with a pet dog between the ages of 5 and 15 also demonstrated a protective effect, dropping risk of CD by 39% (HR, 0.61; P = .025).

“Our analysis revealed a protective trend of living with dogs that transcends the age of exposure, suggesting that dog ownership could confer health benefits in reducing the risk of CD,” the investigators wrote. “Our study also found that living in a large family during the first year of life is significantly associated with the future onset of CD, aligning with prior research that indicates that a larger family size in the first year of life can reduce the risk of developing IBD.”

In contrast, the study identified bird ownership at time of recruitment as a risk factor for CD, increasing risk almost threefold (HR, 2.84; P = .005). The investigators urged a careful interpretation of this latter finding, however, as relatively few FDRs lived with birds.

“[A]lthough our sample size can be considered large, some environmental variables were uncommon, such as the participants having birds as pets, and would greatly benefit from replication of our findings in other cohorts,” Dr Xue and colleagues noted.

They suggested several possible ways in which the above environmental factors may impact CD risk, including effects on subclinical inflammation, microbiome composition, and gut permeability.

“Understanding the relationship between CD-related environmental factors and these predisease biomarkers may shed light on the underlying mechanisms by which environmental factors impact host health and ultimately lead to CD onset,” the investigators concluded.

The study was supported by Crohn’s and Colitis Canada, Canadian Institutes of Health Research, the Helmsley Charitable Trust, and others. The investigators disclosed no conflicts of interest.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.