Associations Between Iron Intake and Serum Iron with Inflammatory Bowel Disease and Chronic Diarrheal Symptoms in Adults: the National Health and Nutrition Examination Survey, 2007-2010

Iron may be involved in the etiology of inflammatory bowel disease (IBD) and chronic diarrhea by modulating gut microbiota and immune responses, but data from epidemiological studies in adults examining this relationship are limited. Thus, the aim of this study was to evaluate the association between iron intake and serum iron levels with IBD and chronic diarrhea in adults. Data from the National Health and Nutritional Examination Surveys (NHANES) between 2007 and 2010 for adults >= 20 years were obtained. Chronic diarrheal symptoms were determined by using the 2007-2010 NHANES questionnaire which included questions pertaining to bowel health. The presence of IBD was analyzed from the NHANES data, directly querying the presence or absence of ulcerative colitis (UC) and Crohn's disease (CD). A total of 9605 participants were initially included in this study. Multivariable logistic regression analysis was used and stratified by gender. Compared with quartile 1 (the lowest quartile), the multivariate-adjusted ORs (95% CI) for risk of having chronic diarrheal symptoms were 1.01 (0.86-1.18), 1.29 (1.07-1.56) and 1.25 (1.02-1.54) across quartiles 2 to 4 of iron intake. This significant association remained among men, but not among women in subgroup analyses. No significant association between either iron intake or serum iron level and the risk of IBD was observed. Generally, there was a positive association between iron intake and chronic diarrheal symptoms in adults that was modified by sex.