TABLE 1.
Environmental risk factors for the inflammatory bowel diseases
| Environmental risk factor |
Strength of association*
|
|
|---|---|---|
| Crohn disease | Ulcerative colitis | |
| Smoking | ||
| Current | Strong positive | Strong negative |
| Previous | Strong positive | Strong positive |
| Never | Negative | Positive |
| Hygiene | ||
| Multiple siblings | Questionable negative | Questionable negative |
| Farm in childhood | Questionable negative | Questionable negative |
| Microorganisms | ||
| Helicobacter pylori | Negative | Negative |
| Helminths | Negative | Negative |
| Myobacterium avium spp paratuberculosis | Positive | Not studied |
| Dysbiosis | Positive | Not studied |
| Urban living environment | Questionable positive | Questionable positive |
| Medication | ||
| Nonsteroidal anti-inflammatory drugs | Positive | Positive |
| Oral contraceptive pills | Positive | Positive |
| Isotretinoin | Questionable positive | Questionable positive |
| Antibiotics | Questionable positive | Questionable positive |
| Appendectomy | Not associated | Negative |
| Nutrition | ||
| Fruits and vegetables | Questionable negative | Questionable negative |
| Fat | Questionable positive | Questionable positive |
| Sugar/sweeteners | Questionable positive | Questionable positive |
| Animal protein | Not studied | Questionable positive |
| Fibre | Questionable negative | Questionable negative |
| Breastfeeding | Questionable negative | Questionable negative |
| Northern residence | Positive | Positive |
| Ambient air pollution | ||
| Sulfur dioxide | Questionable not associated | Questionable positive |
| Nitrogen dioxide in children | Questionable positive | Questionable not associated |
| Nitrogen dioxide in middle-age adults | Questionable negative | Questionable not associated |
| Stress | Questionable positive | Questionable positive |
*
Strength of association based on information from included studies. spp Subspecies