Abstract
Irritable bowel syndrome (IBS) is a common gastrointestinal condition characterized by abnormal bowel habits (diarrhea, constipation, or both), poor mental health, and a reduced quality of life. Although commonly diagnosed through the Rome IV criteria, a universally agreed-upon diagnostic standard for IBS is yet to be established. Several therapeutic modalities are commonly employed to treat IBS, but the lack of a distinct biomarker for the condition makes it challenging for healthcare providers to evaluate the effectiveness of treatments. Elimination diets such as the low FODMAP diet may provide benefits to patients with IBS, however, the accompanying increased risk of nutritional deficiencies may worsen the condition’s symptoms. Vitamin D (VD) supplementation may reduce symptom intensity and enhance the overall quality of life for individuals with IBS through several postulated mechanisms of action, including possible influence on gut microbiota and serotonin levels. This chapter reviews the current evidence from observational studies, systematic reviews, and meta-analyses of randomized controlled trials linking VD deficiency and/or supplementation with IBS. Four observational studies found a connection between diagnosed IBS and patients' vitamin D levels, along with a correlation with symptom severity, while two studies showed contradictory results. Systematic reviews and metaanalyses suggest a positive association between vitamin D supplementation and the relief of IBS symptoms as well as improvements in mental health. Despite these encouraging results, further large-scale clinical trials are needed to establish conclusive findings and enhance clinical approaches for effectively managing IBS.