Researchers from Montefiore Medical Center, Harvard Medical School, and Massachusetts General Hospital have identified factors in low environmental hygiene conditions that lead to less risk for developing inflammatory bowel disease (IBD).
The study, “Environmental Hygiene and Risk of Inflammatory Bowel Diseases: A Systematic Review and Meta-analysis,” published in the journal Inflammatory Bowel Diseases, supports the widely accepted “hygiene hypothesis” that people who are exposed to germs early in life build up healthy resistance against infection and disease. The study suggests that ethnicity may play a role.
To assess the relationship between environmental hygiene and risk of IBD, Dr. Aurada Cholapranee, of Montefiore Medical Center, and Dr. Ashwin N. Ananthakrishnan, of Harvard Medical School and Massachusetts General Hospital, reviewed literature published between 1980 and 2015, on IBD studies that assessed contact with pets and farm animals, number of siblings, bedroom sharing in childhood, and access to personal toilet and hot water. Their analysis was further stratified (listed) by ethnicity.
Results of the meta-analysis (statistical review) revealed that the odds of developing IBD in people who had a dog or a cat during childhood are 24% lower than those who did not own a pet. Having contact with farm animals also reduced the odds of developing IBD by 55%.
Although stratification by ethnicity yielded a similar association with pets in white and non-white cohorts, contact with farm animals was more strongly associated with protection from IBD in non-whites than whites. In fact, non-white cohorts had a 83% decrease in the odds of developing IBD when they reported contact with farm animals; the percentage dropped to 45% for white people.
Sharing a home was inversely associated (less likely to influence) IBD, and with the risk for Crohn’s disease (CD) but not ulcerative colitis (UC). Sharing a bed also seemed be good protective immunity build up against IBD with CD and UC. Such associations were similar both in whites and non-whites, and for exposure in early childhood and in later years.
The risk of developing UC was less likely with having access to a toilet and hot water among non-whites, but not white people. In addition, having two or more siblings, among whites and non-whites, was found to decrease the odds of Crohn’s disease by 7%.
In conclusion, the researchers found robust indications that risk of IBD is lowered by early exposure to pets, farm animals, sharing of bedrooms, and number of siblings. But some exposures ,such as access to toilets or hot water and exposure to farm animals, only showed impacts in specific ethnic groups.