Somatization is associated with altered serum levels of vitamin D, serotonin, and brain‐derived neurotrophic factor in patients with predominant diarrhea irritable bowel syndrome

Abstract

Background Patients with irritable bowel syndrome (IBS) often show psychological disorders, including somatization, usually driven by an altered gut–brain axis. These changes are also accompanied by modifications in the circulating levels of vitamin D (VD) and neurotransmitters such as serotonin (5‐HT) and brain‐derived neurotrophic factor (BDNF). The present study aimed to evaluate the relationship between gastrointestinal (GI) symptoms and circulating levels of VD, 5‐HT, and BDNF in IBS patients with diarrhea (IBS‐D) categorized according to somatization. Methods Fifty‐three IBS‐D patients were recruited and profiled for GI symptoms by validated questionnaires. The fasting serum concentrations of VD, 5‐HT, and BDNF were assessed. The health of the intestinal barrier, minimal inflammation, and dysbiosis was also evaluated. Key Results Thirty patients showed high somatization scores, IBS‐D(S+), and 23 low somatization scores, IBS‐D(S‐). IBS‐D(S+) patients reported higher “Abdominal pain” and the “Abdominal pain duration in days” scores, lower serum VD levels and increased 5‐HT and BDNF concentrations than IBS‐D(S‐). Besides, in IBS‐D(S+) patients, the GI symptoms correlated with 5HT, BDNF, and VD concentrations. These parameters were associated with impaired small intestinal permeability and increased inflammation markers. Conclusions and Inferences These data support the multifactorial IBS pathogenesis in which organic and psychological factors interact. An active role by VD, 5‐HT, and BDNF in affecting the clinical and biochemical profiles in IBS‐D(S+) patients may be conceivable. Therefore, the routine VD estimation and the assay of circulating levels of 5‐HT and BDNF could be considered a new approach for managing these patients.

Vitamin D may alleviate irritable bowel syndrome by modulating serotonin synthesis: a hypothesis based on recent literature

“…In people with insufficient VD levels, VD supplementation may improve the mood of patients by increasing the availability of serotonin in the brain through the expression of TPH2 ( Huiberts and Smolders, 2021 ), while in IBS patients, the disturbance of gut microbiota affects serotonin synthesis in intestinal chromaffin cells ( Linsalata et al, 2023 ), which leads to chronic abdominal pain, and VD can indirectly affect serotonin by improving gut microbiota to relieve abdominal pain.…”