Overview
Vitamin D (calciferol; active form: calcitriol/1,25(OH)₂D₃) is a secosteroid hormone with profound immunomodulatory effects. The vitamin D receptor (VDR) is expressed on virtually all immune cells, and vitamin D deficiency is epidemiologically linked to autoimmune disease (MS, T1D, Hashimoto's, IBD), infection susceptibility, and depression. In the WikiBiome framework, vitamin D connects to the microbiome through antimicrobial peptide induction, Treg support, and direct modulation of gut barrier integrity.
Immune Effects
- Antimicrobial peptides: Vitamin D induces cathelicidin (LL-37) and defensin production — direct antimicrobial effectors at mucosal surfaces.
- Treg support: Vitamin D promotes Treg differentiation and IL-10 production, counterbalancing Th17 responses.
- Th17 suppression: Calcitriol directly inhibits IL-17 production by Th17 cells.
Microbiome Interactions
- Vitamin D supplementation alters gut microbiome composition — increases Bacteroidetes, modulates Firmicutes:Bacteroidetes ratio.
- VDR expression in the gut epithelium regulates barrier integrity and antimicrobial peptide production.
- Vitamin D + probiotic: Combined supplementation (vitamin D + Lactobacillus/Bifidobacterium) improved metabolic parameters in schizophrenia RCT ghaderi 2019 vitamin d probiotic schizophrenia metabolic rct.
Disease Relevance
- MS: Low vitamin D is the strongest environmental risk factor; supplementation reduces relapse rate attfield 2022 immunology ms nature review hoffman 2023 dietary strategies eae ms.
- T1D: Vitamin D deficiency associated with beta-cell autoimmunity bi 2017 omega3 pufa ameliorate t1d autoimmunity.
- Hashimoto's: Part of nutritional prevention strategy puszkarz 2018 food nutrition hashimotos prevention.
- Schizophrenia: Vitamin D + probiotic RCT evidence ghaderi 2019 vitamin d probiotic schizophrenia metabolic rct.
Cross-References
- innate immunity — cathelicidin induction as antimicrobial defense
- th17 treg balance — vitamin D promotes Treg, suppresses Th17
- il 10 — vitamin D drives IL-10 production
- multiple sclerosis — strongest environmental risk factor
- calcium — vitamin D regulates calcium absorption