Background & Aims Increased intake of dietary fiber has been proposed to reduce risk of inflammatory bowel diseases (Crohn’s disease [CD], ulcerative colitis [UC]). However, few prospective studies have examined associations between long-term intake of dietary fiber and risk of incident CD or UC. Methods We collected and analyzed data from 170,776 women, followed over 26 y, who participated in the Nurses’ Health Study, followed for 3,317,425 person-y. Dietary information was prospectively ascertained via administration of a validated semi-quantitative food frequency questionnaire every 4 y. Self-reported CD and UC were confirmed through review of medical records. Cox proportional hazards models, adjusting for potential confounders, were used to calculate hazard ratios (HRs). Results We confirmed 269 incident cases of CD (incidence 8/100,000 person-y) and 338 cases of UC (incidence 10/100,000 person-y). Compared to the lowest quintile of energy-adjusted cumulative average intake of dietary fiber, intake of the highest quintile (median of 24.3 g/day) was associated with a 40% reduction in risk of CD (multivariate HR for CD, 0.59; 95% confidence interval [CI], 0.39–0.90). This apparent reduction appeared to be greatest for fiber derived from fruits; fiber from cereals, whole grains, or legumes did not modify risk. In contrast, neither total intake of dietary fiber (multivariate HR, 0.82; 95% CI 0.58–1.17) nor intake of fiber from specific sources appeared to be significantly associated with risk of UC. Conclusion Based on data from the Nurses’ Health Study, long-term intake of dietary fiber, particularly from fruit, is associated with lower risk of CD but not UC. Further studies are needed to determine the mechanisms that mediate this association.

Introduction Dietary fats influence intestinal inflammation and regulate mucosal immunity. Data on the association between dietary fat and risk of Crohn’s disease (CD) and ulcerative colitis (UC) are limited and conflicting. Methods We conducted a prospective study of women enrolled in the Nurses’ Health Study cohorts. Diet was prospectively ascertained every four years using a validated semi-quantitative food frequency questionnaire. Self-reported CD and UC were confirmed through medical record review. We examined the effect of energy-adjusted cumulative average total fat intake as well as specific types of fat and fatty acids on the risk of CD and UC using Cox proportional hazards models adjusting for potential confounders. Results Among 170,805 women, we confirmed 269 incident cases of CD (incidence 8/100,000 person-years) and 338 incident cases of UC (incidence 10/100,000 person-years) over 26 years and 3,317,338 person-years of follow-up. Cumulative energy-adjusted intake of total fat, saturated fats, unsaturated fats, n-6 and n-3 polyunsaturated fatty acids (PUFA) were not associated with risk of CD or UC. However, greater intake of long-chain n-3 PUFA was associated with a trend towards lower risk of UC (Hazard ratio (HR) 0.72, 95% CI 0.51 – 1.01). In contrast, high long-term intake of trans-unsaturated fatty acids was associated with a trend towards an increased incidence of UC (HR 1.34, 95% CI 0.94 – 1.92). Conclusion A high intake of dietary long-chain n-3 PUFA may be associated with a reduced risk of UC. In contrast, high intake of trans-unsaturated fats may be associated with an increased risk of UC.

Background & Aims Vitamin D influences innate immunity, which is believed to be involved in the pathogenesis of Crohn's disease (CD) and ulcerative colitis (UC). However, data examining vitamin D status in relation to risk of CD and UC are lacking. Methods We conducted a prospective cohort study of 72,719 women (age, 40–73 y) enrolled in the Nurses' Health Study. In 1986, women completed an assessment of diet and lifestyle, from which a 25-hydroxy vitamin D [25(OH)D] prediction score was developed and validated against directly measured levels of plasma 25(OH)D. Through 2008, we confirmed reported diagnoses of incident CD or UC through medical record review. We used Cox proportional hazards modeling to examine the hazard ratio (HR) for incident CD or UC after adjusting for potential confounders. Results During 1,492,811 person-years of follow-up evaluation, we documented 122 incident cases of CD and 123 cases of UC. The median predicted 25(OH)D level was 22.3 ng/mL in the lowest and 32.2 ng/mL in the highest quartiles. Compared with the lowest quartile, the multivariate-adjusted HR associated with the highest quartile of vitamin D was 0.54 (95% confidence interval [CI], 0.30–.99) for CD (Ptrend = .02) and 0.65 (95% CI, 0.34–1.25) for UC (Ptrend = .17). Compared with women with a predicted 25(OH)D level less than 20 ng/mL, the multivariate-adjusted HR was 0.38 (95% CI, 0.15–0.97) for CD and 0.57 (95% CI, 0.19–1.70) for UC for women with a predicted 25(OH)D level greater than 30 ng/mL. There was a significant inverse association between dietary and supplemental vitamin D and UC, and a nonsignificant reduction in CD risk. Conclusions Higher predicted plasma levels of 25(OH)D significantly reduce the risk for incident CD and nonsignificantly reduce the risk for UC in women.

Objective Geographical variation in the incidence of Crohn’s disease (CD) and ulcerative colitis (UC) according to the latitude of residence has been reported in Europe. However, there are no comparable data in the USA. The incidence of CD and UC in relation to latitude was assessed in a geographically diverse population of women enrolled in two large prospective studies in the USA. Design A prospective study was undertaken of women enrolled in the Nurses’ Health Study I (NHS) in 1976 and in the NHS II in 1989. Information on state of residence at the time of birth, at age 15 years and age 30 years was collected in 1992 in NHS I and in 1993 in NHS II. Reported diagnoses of incident CD or UC to the end of 2003 were confirmed by medical record review. Cox proportional hazards models were used to calculate HRs and 95% CIs for risk of CD and UC. Results In both cohorts, among 175 912 women reporting their residence in 1992, 257 cases of CD and 313 cases of UC were documented over 3 428 376 person-years of follow-up. The incidence of CD and UC increased significantly with increasing latitude (ptrend<0.01), with residence at age 30 years more strongly associated with risk. Compared with women residing in northern latitudes at age 30, the multivariate-adjusted HR for women residing in southern latitudes was 0.48 (95% CI 0.30 to 0.77) for CD and 0.62 (95% CI 0.42 to 0.90) for UC. The effect of latitude of residence on risk of CD and UC did not vary according to smoking history (pinteraction=0.26 for CD and 0.99 for UC). Conclusion In a population of US women, increasing latitude of residence was associated with a higher incidence of CD and UC.

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Background Oral contraceptive use has been associated with risk of Crohn’s disease (CD) and ulcerative colitis (UC). Objective To determine whether this association is confounded or modified by other important lifestyle and reproductive factors. Design A prospective cohort study was carried out of 117 375 US women enrolled since 1976 in the Nurses Health Study I (NHS I) and 115 077 women enrolled since 1989 in the Nurses’ Health Study II (NHS II) with no prior history of UC or CD. These women had provided information every 2 years, on age at menarche, oral contraceptive use, parity, menopause status and other risk factors. Diagnoses of CD and UC were confirmed by review of medical records. Cox proportional hazards models were used to calculate HRs and 95% CIs. Results Among 232 452 women with over 5 030 196 person-years of follow-up, 315 cases of CD and 392 cases of UC were recorded through 2007 in NHS II and 2008 in NHS I. Compared with never users of oral contraceptives, the multivariate-adjusted HRs for CD were 2.82 (95% CI 1.65 to 4.82) among current users and 1.39 (95% CI 1.05 to 1.85) among past users. The association between oral contraceptives and UC differed according to smoking history (pheterogeneity = 0.04). Age at menarche, age at first birth and parity were not associated with risk of UC or CD. Conclusion In two large prospective cohorts of US women, oral contraceptive use was associated with risk of CD. The association between oral contraceptive use and UC was limited to women with a history of smoking.

Background & Aims Long-term data on the influence of cigarette smoking, especially cessation, on the risk of Crohn’s disease (CD) and ulcerative colitis (UC) are limited. Methods We conducted a prospective study of 229,111 women in the Nurses’ Health Study (NHS) and Nurses’ Health Study II (NHS II). Biennially, we collected updated data on cigarette smoking, other risk factors, and diagnoses of CD or UC confirmed by medical record review. Results Over 32 years in NHS and 18 years in NHS II, we documented 336 incident cases of CD and 400 incident cases of UC. Compared to never smokers, the multivariate hazard ratio (HR) of CD was 1.90 (95% confidence interval [CI], 1.42–2.53) among current smokers and 1.35 (95% CI, 1.05–1.73) among former smokers. Increasing pack-years was associated with increasing risk of CD (Ptrend< 0.0001) whereas smoking cessation was associated with an attenuation of risk. In contrast, the multivariate HRs of UC was 0.86 (95% CI, 0.61–1.20) among current smokers and 1.56 (95% CI, 1.26–1.93) among former smokers. The risk of UC was significantly increased within 2 to 5 years of smoking cessation (HR, 3.06; 95% CI, 2.00–4.67) and remained persistently elevated over 20 years. Conclusions Current smoking is associated with an increased risk of CD, but not UC. In contrast, former smoking is associated with an increased risk of UC, with risk persisting over two decades after cessation.

Introduction Obesity is associated with intestinal-specific inflammation. Nonetheless, a specific role of obesity in the etiology of inflammatory bowel disease (IBD) is unclear. Methods We conducted a prospective cohort study of U.S. women enrolled in 1989 in the Nurses’ Health Study II. At baseline, we collected information on height, weight, waist and hip circumference, weight at age 18, and body shape at age 20. We used Cox proportional hazards models to calculate hazard ratios (HR) and 95% confidence intervals (CIs). Results Among 111,498 women (median age, 35 years), we documented 153 cases of CD and 229 cases of UC over 18 years of follow-up, encompassing 2,028,769 person-years. Compared to women with normal BMI, the multivariate-adjusted HRs of CD were2.33 (95% CI, 1.15–4.69) for obese women at age 18 and 1.58 (95% CI, 1.01–2.47) for obese women at baseline. Increasing weight gain between age 18 and baseline was associated with increased risk of CD (Ptrend=.04). Adolescent body habitus was also associated with risk of CD with a multivariate-adjusted HR of CD of 1.63 (95% CI, 1.07–2.50) for women with overweight/obese body shape compared to women with a thin/slender body shape. We did not observe a significant association between any of these anthropometric measures and risk of UC. Conclusion In a large prospective cohort of US women, measures of adiposity were associated with an increased risk of CD but not UC. Further studies are needed to elucidate the biological mechanisms by which excess adiposity may increase the risk of CD.