The Relationship between Low Serum Vitamin D Levels and Altered Intestinal Barrier Function in Patients with IBS Diarrhoea Undergoing a Long-Term Low-FODMAP Diet: Novel Observations from a Clinical Trial

Abstract

Decreased serum vitamin D (VD) levels have been associated with gastrointestinal (GI) disorders, including irritable bowel syndrome (IBS). VD can also modulate the intestinal barrier. Given the link between the GI barrier’s alterations and diet, attention has aroused the positive effects of the Low FODMAP Diet (LFD) on IBS patients’ symptom profile. We evaluated the GI symptoms and the urinary and circulating markers of GI barrier function, the markers of inflammation and intestinal dysbiosis in 36 IBS patients with predominant diarrhea (IBS-D) (5 men and 31 women, 43.1 ± 1.7 years) categorized for their circulating VD levels in low (L-VD) and normal (N-VD) (cutoff = 20 ng/mL). Evaluations were performed before and after 12 weeks of LFD. At the baseline, L-VD patients showed a significantly worse symptom profile and altered small intestinal permeability (s-IP) than N-VD. After LFD, a significant increase in the circulating VD levels in both the subgroups and a significant improvement of s-IP in L-VD patients occurred. Finally, VD levels negatively correlated with the symptom score and fecal zonulin. These data highlight the close relationship between VD and the intestinal barrier and support their involvement in IBS-D pathophysiology. Moreover, the potentially positive role of LFD in the management of IBS-D was confirmed.

Psychological and Gastrointestinal Symptoms of Patients with Irritable Bowel Syndrome Undergoing a Low-FODMAP Diet: The Role of the Intestinal Barrier

“…As demonstrated in our previous paper [25], the urinary percentage of mannitol decreased significantly at the end of the diet. The recovery of this non-absorbable sugar gives information on the transcellular pathway, and its reduction could be attributed to an improvement in food intolerance/malabsorption in the small intestine due to the reduced intake of FODMAPs.…”

“…After fasting overnight, the subjects drank a test solution with lactulose (10 g), mannitol (5 g), and sucrose (40 g) in a volume of 100 mL. The evaluation of the three sugars in urine was performed by chromatographic analysis as previously reported [ 18 , 25 ]. The percentage of the ingested sugars (%lactulose, %mannitol, and %sucrose) was evaluated.…”

“…A standard colorimetric assay kit (indican assay kit, ABnova Corporation, Taipei, Taiwan) was used according to the manufacturer’s procedure. The detection and measurement of skatole in urine were carried out on a high-performance liquid chromatography (HPLC) system using a 3-methylindole kit (EurekaLab Division, Chiaravalle, AN, Italy), as described previously [ 25 ]. Urine indican and skatole values higher than 20 mg/L and 20 μg/L are considered as indicators of fermentation and putrefactive dysbiosis [ 38 , 39 ].…”

“…The study protocol and the intervention diet have previously been published in openaccess articles [18,25], and the clinical trial was registered on http://www.clinicaltrials.gov (NCT03423069)-last accessed data: 17 February 2021. The study was approved by the local Scientific Committee and the Ethics Committee of IRCCS Istituto Tumori Giovanni Paolo II-Oncological Hospital, Bari, Italy, 274/C.E.…”

“…Most IBS patients attribute their condition to some foods, such as the fermentable oligosaccharides, disaccharides, monosaccharides, and polyols (FODMAPs) [ 23 , 24 ], and many papers have demonstrated a positive effect of the low FODMAP diet (LFD) on the IBS-D symptoms [ 25 ]. However, limited data are still available on the LFD effects on non-GI symptoms, i.e., the psychological symptoms and impaired QoL, often complained about by these patients [ 26 ].…”