July 04, 2025

186. The Gut-Immune Axis, Intestinal Barrier Function, & Vitamin D₃ | Activated 1,25-dihydroxyvitamin D₃ and Immune Function, Vitamin D Testing, & More

14 minutes

In this encore episode, we highlight vitamin D₃ in gastrointestinal health, with a focus on intestinal barrier function and the gut-immune axis. We discuss how vitamin D is metabolized into its active form, 1,25-dihydroxyvitamin D, and how 1,25-dihydroxyvitamin D can support the intestinal mucosa, while highlighting the intestinal epithelium and immune cells in the lamina propria. Through this, we further detail the role of regulatory T cells in supporting immune balance and modulating immune function.

Topics:

1. Introduction

- Highlighting intestinal barrier function and the gut-immune axis with a focus on vitamin D₃

2. Vitamin D Synthesis and Metabolism

- Skin and 7-dehydrocholesterol; dietary intake.

- Transported through the bloodstream bound to vitamin D binding protein.

- First hydroxylation in the liver to form 25-hydroxyvitamin D₃ (25(OH)D₃).

- Testing.

- Second hydroxylation in the kidney to form the active 1,25 dihydroxyvitamin D₃ (1,25(OH)₂D₃).

- Local activation also occurs.

3. Intestinal Barrier Anatomy

- The intestinal epithelium forms a selectively permeable monolayer that interfaces with the gut lumen.

- Covered by a mucus layer: mucins, antimicrobial peptides, secretory IgA.

- Mucus layer provides physical and biochemical protection.

- Tight junction proteins and paracellular permeability.

- Molecules crossing the epithelium.

- Disruption of tight junctions, immune cell exposure to luminal contents.

- The lamina propria and Gut-Associated Lymphoid Tissue (GALT).

- Maintaining tolerance while defending against pathogens.

4. Vitamin D’s Role in Barrier Support and Immune Modulation

- 1,25-dihydroxyvitamin D₃, tight junction integrity, immune regulation, and more.

- Regulatory T Cells (Tregs) and immune balance.

5. Vitamin D₂ and D₃

- D₃ (cholecalciferol) is more biologically effective and binds DBP more strongly.

6. Vitamin D Levels

- Levels observed in autoimmune conditions, IBS, and more.

- Symptoms.

- Insufficient and excessive levels of vitamin D can be detrimental.

- Multi-system.

7. Conclusion

- Multifactorial: Numerous factors regulate vitamin D levels.

- Gastrointestinal health root cause approach.

Thanks for tuning in!

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