The pathogenesis of inflammatory bowel disease (IBD) highlights the role of mucosal immunology and changes in the gut microbiome triggered by genetic and environmental factors including diet regiments, as suggested by many nutritional studies. Along with medications usually used for IBD treatment, therapeutic strategies also include the supplementation of micronutrients such as vitamin D, folic acid, iron, and zinc.
1. Introduction
The pathogenesis of inflammatory bowel disease (IBD) highlights the role of mucosal immunology and changes in the gut microbiome triggered by genetic and environmental factors including diet regiments, as suggested by many nutritional studies
[1,2,3,4][1][2][3][4]. Oxidative damage that occurs in CD and UC is a result of an altered balance between free radical production with antioxidant depletion and micronutrients, leading to antioxidant repletion
[1,2,3,4][1][2][3][4]. The presence or absence of anti-inflammatory agents such as antioxidants obtained through dietary intake or supplementation can impact the course of IBD. The intestinal tissue damage and altered gut microbiota caused by oxidative stress are significantly impacted by the presence of tissue repair mediators. Modulating the intestinal microbiota remains an attractive therapeutic potential for IBD
[1,2,3,4][1][2][3][4]. Changes in dietary habits were also found to be strongly associated with a determined increased risk of autoimmune disease in a pediatric population
[5,6][5][6]. So far, dietary constituents have been considered precipitants or promoters of complex interactions in IBD pathology, while nutritional deficiency with imbalances of specific micronutrients has been associated with the course of the disease
[1,2][1][2]. Nevertheless, the role of modifiable environmental and behavioral factors such as diet remains poorly understood.
The majority of IBD patients show an interest in the active management of their disease, especially through dietary modifications
[7]. Specifically, long-term dieting has shown the most significant effect in shaping the intestinal microbiome
[8]. Therapeutic strategies in IBD, along with medications, encompass nutritional interventions including not only the elimination of potential food triggers but also the improvement of the nutritional status of patients
[1,2,9][1][2][9]. The supplementation of micronutrients and macronutrients is important in everyday clinical practice in reducing the primary or secondary symptoms of disease
[2]. Nevertheless, overuse or treatment with doses far exceeding the recommended daily allowances can be harmful and lead to adverse effects on the course of IBD. Especially during the coronavirus (COVID-19) pandemic, the frequent use of over-the-counter supplements among IBD patients has contributed to inadequate and uncontrolled strategies in therapy management.
2. Role of Vitamins in Inflammatory Bowel Disease
2.1. Vitamin D
According to numerous investigations, the deficiency of vitamin D has been highlighted as a key factor in the pathogenesis of IBD (
Table 1)
[21,22][10][11]. Vitamin D is a liposoluble vitamin, and its hormonal form of 1,25-dihydroxy vitamin D3 [1,25(OH)2D3], also called calcitriol, is important for various pathways of the immune system mediated via nuclear vitamin D receptor (VDR) in immune cells such as T and B lymphocytes, monocytes and macrophages. Vitamin D has a role in immune cell differentiation, the modulation of the gut microbiota, gene transcription, and barrier integrity
[22][11]. A reduction in the serum levels of vitamin D is associated with an increased risk for infection (
Table 1)
[21,22][10][11]. The role of vitamin D includes the support of intestinal epithelial junctions and the upregulation of junction proteins including claudins, ZO-1, and occludins. The disruption of the mucosal barrier was noted in an IBD investigation in polarized epithelial Caco-2bbe cells grown in a medium with or without vitamin D and challenged with adherent invasive
E. coli strain (AIEC). The investigation showed that Caco-2bbe cells incubated with 1,25(OH)2D3 were protected against AIEC-induced disruption. Additionally, vitamin D-deficient mice with DSS-induced colitis showed significant increases in the quantities of
Bacteroidetes and were more susceptible to AIEC colonization. According to previous studies, vitamin D contributes to the homeostasis of the intestinal barrier function and protection against adherent invasive
E. coli [23][12]. Additionally, it has been suggested that patients with IBD are at an increased risk of
Clostridium difficile infection. Vitamin D has a prophylactic role against infection, influencing the production of antimicrobial compounds such as cathelicidins and modulating the microbiome
[24][13]. VDR regulates the biological action of 1,25(OH)2D3 and has a role in the genetic, immune, environmental and microbial aspects of IBD. Dionne at al. study indicated that 1,25(OH)2D3 in CD patients significantly decreases the proinflammatory activity of M1-type macrophage but does not provide a reduction in the anti-inflammatory actions of M2-type macrophages. The level of anti-inflammatory cytokine IL-10 was not affected in the investigation
[25][14]. The deficiency of vitamin D is also correlated with disease activity in IBD patients, so administration targeting a concentration of 30 ng/mL could potentially reduce disease activity
[22][11]. Even though reports have shown lower vitamin D levels in IBD patients compared with the healthy population, it is not clear yet if the vitamin D deficiency is a consequence of the disease itself or if it has a role in disease pathogenesis. A study that followed subjects in two time points before (up to 8 years) and one time point after IBD diagnosis showed that the vitamin D level was not altered in IBD patients prior to disease onset compared with matched controls, but it was reduced after the disease was established
[26][15].
Table 1.
Frequent deficiencies of micronutrients in IBD.