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

Table 2 Environmental factors and onset of inflammatory bowel disease - cohort studies

Author	Study subjects	Effect on CD	Effect on UC
Timm et al[76], 2014, Europe	Population-based cohort	DR with being born and living on livestock farm for first 5 yr of life
	10864 subjects from ECRHS1 cohort
	Outcome - place of upbringing and risk of IBD
Khalili et al[53], 2013, United States	146681 subjects from NHS I and II	NA - Breastfeeding, low or high birth weight, preterm birth	NA - Breastfeeding, low or high birth weight, preterm birth
	3373726 person-years of follow-up
	Outcome - risk of IBD in adulthood
Ananthakrishnan et al[31], 2013, United States	170776 subjects from NHS I and II	DR - Long term intake of higher dietary fibre especially from fruit	NA with dietary fibre
	3317425 person-years of follow-up
	Outcome - diet and risk of IBD in adulthood
Ananthakrishnan et al[84], 2013, United States	152461 subjects from NHS I and II	IR with recent and baseline depressive symptoms	NA with recent and baseline depressive symptoms
	1787070 person-years of follow-up
	Outcome - Depressive symptoms and risk of IBD
Levi et al[75], 2013, Israel	Cohort of 953684 Jewish adolescents	IR with high socioeconomic status, western origin, male sex
	Outcome - sociodemographic factors and risk of IBD	DR with four or more children in childhood
Higuchi et al[38], 2012, United States	229111 subjects from NHS I and II	IR - Current smoker, former smoker	NA - Current smoker
	Outcome - Smoking and risk of IBD		IR - Former smoker
Ananthakrishnan et al[56], 2012, United States	76795 subjects from NHS I	IR - frequent use of NSAID	IR - frequent use of NSAID
	1295317 person-years of follow-up
	Outcome - NSAID and aspirin exposure and risk of IBD	NA - Aspirin	NA - Aspirin
Ananthakrishnan et al[48], 2012, United States	72719 subjects from NHS	DR - Higher predicted level of plasma Vitamin D	NA - Vitamin D level in plasma
	1492811 person-years of follow-up
	Outcome - Vitamin D and risk of IBD

¹European Community Respiratory Health Survey. IR: Increased risk; DR: Decreased risk; NA: No association; CD: Crohn’s disease; UC: Ulcerative colitis; RR: Relative risk; IBD: Inflammatory bowel disease; NSAID: Nonsteroidal anti-inflammatory drug; NHS: Nurses Health Study.