Too much hygiene: CD in later life?

Different environmental factors influence inflammatory bowel disease (IBD) risk in first-degree relatives of patients with Crohn’s disease (CD). Living with a dog and in a large family were both protective factors, adding to the existing evidence that too much hygiene might be responsible for an elevated risk for CD.

“Our study seems to add to others that have explored the ‘hygiene hypothesis’ which suggests that the lack of exposure to microbes early in life may lead to a lack of immune regulation towards environmental microbes,” said Dr Williams Turpin (Mount Sinai Hospital and the University of Toronto, Canada). In the study, an environmental questionnaire was used to collect information from nearly 4,300 first-degree relatives of people with CD enrolled in the Crohn’s and Colitis Canada Genetic, Environmental, and Microbial (CCC-GEM) project [1]. Using responses to the questionnaire and historical data collected at the time of recruitment, Dr Turpin and his team analysed several environmental factors, including family size, the presence of dogs or cats as household pets, the number of bathrooms in the house, living on a farm, drinking unpasteurised milk, and drinking well water. The analysis also included age at the time of exposure.

As a secondary analysis, regression models were used to identify the relationship of exposures with biological factors associated with CD risk: intestinal permeability using urinary fractional excretion of lactulose to mannitol ratio (LMR), with LMR ≥0.025 defined as abnormal; subclinical inflammation using faecal calprotectin (FCP), with FCP ≥100 μg/g; and faecal microbiome composition and diversity using 16S rDNA sequencing.

After a 5.6-year median follow-up time, 86 first-degree relatives developed CD. Living with a dog between ages 2–4 (HR 0.63; 95% CI 0.44–0.99) and large family size (>3) in the first year (HR 0.36; 95% CI 0.18–0.72) were significantly associated with lower risk of CD onset. Family size in the first year was not associated with changes in parameters assessed in the secondary analysis. In contrast, owning a dog between the ages of 2–4 was significantly associated with normal LMR. Similar effects were observed with exposure to dogs across all age groups.

“We did not see the same results with cats as pets, though we are still trying to determine why,” Dr Turpin said. “It could potentially be because dog owners get outside more often with their pets or live in areas with more green space, which has been shown previously to protect against CD.”

These findings may assist physicians in assessing patients at high risk for developing IBD. A limitation of the study is that the early-life environmental factors were assessed by questionnaires, so caution is warranted in interpreting these results due to possible recall bias at recruitment.

1. Turpin W et al. Environmental factors associated with risk of Crohn’s disease (CD) development in a prospective cohort of healthy first-degree relatives of CD patients. Lecture 793, Digestive Disease Week 2022, 21–24 May, San Diego, CA, USA.

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Posted on 14 June 20228 April 2024