Background: Increased dairy consumption has been linked to the development of chronic inflammatory disorders and autoimmune diseases. Little research has been done to explore the relationship between dairy consumption and risk of inflammatory bowel disease (IBD). We therefore sought to investigate the association between dairy intake and the risk of IBD using 3 large, prospective cohort studies of US men and women: the Nurses’ Health Study (NHS), Nurses’ Health Study II (NHSII) and the Health Professionals Follow-up Study (HPFS).
Methods: We included 197,765 participants without a baseline diagnosis of IBD in 1986 in NHS, 1991 in NHSII, and 1986 in HPFS. Dietary data were collected every 2-4 years using a semi-quantitative validated food frequency questionnaire. Total dairy intake was divided into quintiles while components of dairy (which included ‘skim/low fat milk’, ‘whole milk’, ‘cheese’, ‘butter’, ‘cream’, ‘sherbet’, ‘ice-cream’,and ‘yogurt’) were modeled as quartiles. We used Cox proportional hazard modeling to estimate adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs) while adjusing for age, body mass index, smoking, physical ativity, and total caloric, dietary fiber and fat intakes. Latency analyses, which examines the relationship between dairy consumption and risk of IBD according to various time windows, were also conducted.
Results: Through the end of follow up (2016 for NHS and HPFS, and 2017 for NHSII), we documented 347 Crohn’s disease (CD) cases and 428 ulcerative colitis (UC) cases over 4,934,129 person-years. In our primary analysis, we observed a non-significant inverse association between total dairy intake and risk of UC (P_trend=0.128) (Table 1). Compared to participants in the lowest category of dietary dairy intake, the aHRs for UC were 0.85 (95%CI 0.63-1.14) and 0.84 (95%CI 0.62-1.12) for the highest categories. There was no asscociation between total dairy intake and risk of CD (P_trend=0.822). In our latency analysis, we observed that the inverse association between total dietary dairy and risk of UC strengthened as the exposure to outcome time window increased. This reached statistical significance when baseline dairy intake was used (Table 2). Compared with individuals in the lowest quintile of dairy intake, those in the highest quintile had an aHR of 0.71 (95%CI 0.52-0.96, P_trend=0.017). Among components of dairy, baseline yogurt consumption (HR= 0.68; 95%CI 0.48-0.96; P_trend=0.028) was most strongly associated with risk of UC. We observed no association between total dairy intake or any of its components and risk of CD in our latency analyses.
Conclusion: In three large prospective cohort studies, we observed a suggestive inverse association between total dairy intake, particularly from yogurt, and risk of UC. The association was strongest when dietary data from more than 8 years before diagnosis was used.

Table 1. Dairy intake by quintile and risk of Crohn’s disease and ulcerative colitis

Table 2. Total dairy consumption in quintiles and Crohn’s disease and ulcerative colitis risk, latency analysis

Kevin Casey

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