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Hygiene Hypothesis: Is the Evidence the Same All Over the World?
Rupert W Leong1, Nikola Mitrev, Yanna Ko
1Gastroenterology and Liver Services, Concord Hospital, Sydney, N.S.W., Australia.
Digestive Diseases (Basel, Switzerland)
|March 17, 2016
Summary
The hygiene hypothesis, linking reduced microbial exposure to immune diseases, is not universally applicable. Its relevance varies with societal affluence and migration patterns, impacting inflammatory bowel disease (IBD) risk differently across populations.
Area of Science:
- Epidemiology
- Immunology
- Microbiology
Background:
- The hygiene hypothesis suggests modern living conditions, with improved hygiene, reduce microbial exposure, potentially increasing immune-related diseases like inflammatory bowel diseases (IBD).
- Reduced enteric microbiota diversity and dysbiosis are implicated in IBD development due to decreased exposure to microbes.
Purpose of the Study:
- To investigate the global applicability of the hygiene hypothesis in the context of inflammatory bowel diseases (IBD).
- To examine how varying levels of societal affluence and migration influence the relationship between hygiene, microbial exposure, and IBD risk.
Main Methods:
- Review of global data linking the hygiene hypothesis to IBD development.
- Comparative analysis of risk factors in different populations, including affluent versus less-affluent countries and migrant populations.
- Utilizing proxy markers for hygiene, such as GDP and infection risk factors, due to the difficulty in direct measurement.
Main Results:
- The hygiene hypothesis is most relevant in societies experiencing increasing affluence or in migrant populations moving to more affluent countries.
- Environmental risk factors for IBD differ between native Caucasian Australians and Middle Eastern migrants, with hygiene-related factors less relevant for long-term residents of affluent nations.
- In contrast to the hypothesis, infection risk factors were positively associated with ulcerative colitis in India, not protective.
- Childhood antibiotic use increases IBD risk in developed societies but may also be a risk factor for IBD in migrants.
Conclusions:
- The hygiene hypothesis's applicability is context-dependent, primarily relevant to populations undergoing economic development or migration.
- Divergent findings highlight the complexity of IBD etiology, influenced by a combination of genetic, environmental, and microbial factors that vary geographically and socioeconomically.
- Further research is needed to refine our understanding of hygiene, microbial exposure, and IBD development across diverse global settings.
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