Table 1.

Effect of environmental factors on rates of IBD.

Factor	General effect on rates of IBD
South to North migration	Increase
East to West migration	Increase
Smoking	Reduction [UC]; increase [CD]
Appendectomy	Reduction [UC]; increase [CD]
Antibiotics in childhood	Increase [Western populations]; reduction [Asia]
Improved hygiene/sanitation	Increase
COX inhibition	Increase [NSAIDs, aspirin]; reduction [COX2-inhibitors]
Reduced dietary fibre	Increase [CD]
High ω-6:ω-3 PUFA	Increase
Vitamin D deficiency	Increase
Stress	Increase
Increased physical activity	Reduction

COX, cyclo-oxygenase; PUFA, polyunsaturated fatty acids; NSAID, non steroidal anti-inflammatory drug; CD, Crohn’s disease; UC, ulcerative colitis.

Data extracted from reference 35.