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

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.