Influence of environmental factors on the onset and course of inflammatory bowel disease

Table 1 Environmental factors and onset of inflammatory bowel disease - meta-analyses

Author	Study setting	Effect on CD	Effect on UC	Effect on IBD overall
Soon et al[63], 2012	Urban living and risk of CD and UC	IR (incident rate ratio, 1.42; 95%CI: 1.26-1.6)	IR (incident rate ratio, 1.17; 95%CI: 1.03-1.32)
Luther et al[70], 2010	H. pylori infection and risk of IBD, (23 studies)			DR (RR = 0.64; 95%CI: 0.54-0.75)
Barclay et al[50], 2009	Breast feeding and early onset IBD (7 studies)	NA	NA	DR (OR = 0.69; 95%CI: 0.51-0.94)
Jones et al[42], 2008	Prenatal or childhood passive smoking and risk of IBD (13 studies)	NA	NA
Cornish et al[54], 2008	OCP and risk of IBD (14 studies)	IR (RR = 1.46 ; 95%CI: 1.26-1.70)	IR (RR = 1.28 ; 95%CI: 1.06-1.54)
Mahid et al[37], 2007	Smoking and risk of IBD (13 studies related to UC and 9 related to CD)	IR with current smoking (OR = 1.76; 95%CI: 1.40-2.22)	DR with current smoking (OR = 0.58; 95%CI: 0.45-0.75)
			IR with former smoking (OR = 1.79; 95%CI: 1.37-2.34)

IR: Increased risk; DR: Decreased risk; NA: No association; CD: Crohn’s disease; UC: Ulcerative colitis; RR: Relative risk; IBD: Inflammatory bowel disease; OCP: Oral contraceptive pill.