Living with a dog between ages 5 and 15 is associated with a lower risk of Crohn's disease in first-degree relatives of patients, according to a new prospective cohort study.
A prospective cohort study, published in Clinical Gastroenterology and Hepatology, identified several environmental factors associated with the risk of developing Crohn's disease (CD) in first-degree relatives of CD patients. Along with the association with living with a dog early in life, the study also identified associations with living in a household with 3 or more individuals during the first year of life as a protective environmental factor. Living with birds at the time of recruitment into the study, and having a sibling with CD were both identified as factors that increased the risk of developing CD.
The study also looked at associations between various environmental factors and pre-disease biomarkers, finding participants who lived with dogs between ages 5 to 15 exhibited significantly lower lactulose to mannitol ratio and were less likely to have abnormal gut permeability. Participants who lived with birds at the time of recruitment were more likely to exhibit subclinical inflammation as measured by fecal calprotectin assessments.
Dog ownership during youth was also associated with increased alpha diversity in the gut microbiome. This cohort of the study was found to have a higher abundance of Frisingicoccus, Incertae_Sedis, Adlercreutzia, Ruminococcaceae_UBA1819, and Phascolarctobacterium, and a lower abundance of Senegalimassilia, Lactobacillus, Dialister, and Lachnospiraceae_UCG-004.
The study found consistent microbial differences across various age groups for dog ownership. Six genera (Senegalimassilia, Lactobacillus, Incertae_Sedis, Frisingicoccus, Dialister, and Adlercreutzia) were consistently different in participants who lived with a dog in any age group.
The study followed 4,289 healthy first-degree relatives over a median of 5.62 years, during which 86 participants developed CD. The study analyzed data from the Crohn's and Colitis Canada - Genetic, Environmental, Microbial (CCC-GEM) project. Participants aged 6–35 years completed an Environmental Risk Assessment questionnaire at recruitment. Cox proportional hazards models were used to identify environmental factors associated with CD onset.
The cohort's median recruitment age was 17.0 years, with 47% being male. Participants who remained healthy were older at recruitment than those who developed CD. There were no significant differences in terms of sex, self-reported ethnicity, or country of birth.
The authors note that use of questionnaire-based assessments may be subject to recall bias, the use of single-point measurements of biological markers limits the assessment of temporal variability, and the small sample sizes for some environmental exposures (e.g., bird ownership) may limit generalizability.
The study identified environmental exposures associated with CD onset in first-degree relatives of CD patients and explored potential mechanisms through pre-disease biomarkers. Further research may be needed to confirm these findings and elucidate underlying mechanisms.
The authors declared having no competing interests.
