Vitamin metabolism

1. Vitamin D Metabolism
Presented by : R.ArunaDevi
25MIM049

2. Introduction
• Fat-soluble vitamin acting as a prohormone.
• Important for calcium & phosphate balance,
bone health, immunity.
• Obtained from sunlight, diet, and
supplements.
• Requires activation in liver and kidney.

3. Sources of Vitamin D
• Endogenous: Skin synthesis (UVB → Vitamin
D₃)
• Exogenous (dietary sources)
• Vitamin D₂ (plants, fortified foods)
. Vitamin D₃ (fish oil, egg yolk, dairy products)

5. Skin
• 7-dehydrocholesterol in skin absorbs UVB
(290–315 nm)
• Converts to Pre-vitamin D₃
• Thermal conversion → Vitamin D₃
(cholecalciferol)
• Factors: skin color, age, sunscreen, geography
• Vitamin D₃ enters blood bound to DBP → Liver

6. Liver
• Enzyme: 25-hydroxylase (CYP2R1)
• Vitamin D (D₂ or D₃) → 25-hydroxyvitamin D
[25(OH)D, Calcidiol]
• Main circulating storage form
• Used for blood tests to assess Vitamin D status

8. Kidney
• Enzyme: 1α-hydroxylase (CYP27B1)
• 25(OH)D → 1,25-dihydroxyvitamin D
[1,25(OH)₂D, Calcitriol]
• Active hormone form
• Regulated by PTH, calcium, phosphate, and
FGF23

10. Regulation
• Parathyroid Hormone (PTH): ↑ calcitriol
production.
• Calcium & phosphate: feedback control.
• FGF23: inhibits excess calcitriol production.

11. Functions of Vitamin D
• Intestine: ↑ absorption of calcium &
phosphate
• Bone: promotes mineralization & remodeling
• Kidney: reduces calcium excretion
• Immune system: modulates defense
mechanisms

12. Disorders of Vitamin D
• Deficiency:
- Rickets (children)
- Osteomalacia (adults)
- Osteoporosis (elderly)
• Excess:
- Hypercalcemia
- Kidney stones
- Organ damage

13. Clinical Importance
• Blood test measures 25(OH)D (not active
calcitriol).
• Normal range: 30–50 ng/mL.
• Vitamin D₃ supplements preferred.
• Used in osteoporosis, CKD,
hypoparathyroidism treatment.

14. Conclusion
• Vitamin D acts as a hormone regulating
calcium-phosphate balance.
• Synthesized in skin, activated in liver & kidney.
• Active form (calcitriol) affects intestine, bone,
kidney, immune system.
• Both deficiency and excess cause health
problems.

15. REFERENCE :
Holick MF. Vitamin D Deficiency. N Engl J Med.
2007.
DeLuca HF. Overview of general physiologic
features and functions of vitamin D. Am J Clin
Nutr. 2004.
• Bikle DD. Vitamin D metabolism, mechanism
of action, and clinical applications. Chem Biol.
2014.