Vitamin D is important for regulating calcium and phosphate levels. It is synthesized in the skin from 7-dehydrocholesterol and the active form is produced in the kidneys. As a hormone, it has target organs and its action is similar to steroid hormones. A deficiency can lead to bone deformities like rickets in children and osteomalacia in adults due to incomplete mineralization of bones. Toxicity from too much vitamin D can cause hypercalcemia and kidney stones.

1. VITAMIN D

2. Chemistry
Plants Ergocalciferol Vitamin D2
Cholecalciferol Vitamin D3
Animals
7-dehydrocholesterol
Provitamins
25- Hydroxy Cholecalciferol
1,25- DiHydroxy Cholecalciferol
• Absorbed in the small intestine.
• Through lymph, enters the circulation bound to plasma a2-globulin and is
distributed throughout the body.
Ca2+
P
25-
hydroxycholecalicf
erol 1-hydroxylase
Parathyroid
Active Form of Vitamin D

3. Functions
Regulates the plasma Ievels of calcium and phosphate
Absorption of calcium
and phosphate
Via calcium binding
protein Mobilization of calcium and
phosphate from the bone.
Plasma calcium and phosphate
PT
Ca uptake for deposition as
calciumphosphate = Bone
formation
Rebsorption of Ca &
phosphate
Excretion of Ca &
phosphate

4. Hormone/ Vitamin ?
• Synthesized in the skin
• Active form produced in
• Has target organs
• Action similar to steroid hormones
• Synthesis is self-regulated

5. Deficiency
Bone deformities due to incomplete mineralization, soft and pliable bones and delay in
teeth formation.
The weight bearing bones are bent = Bow-legs.
Plasma level of calcitriol
Alkaline phosphatase activity
Rickets
Osteomalacia
Children
Adults
Demineralization = Fractures

6. Toxicity
Hypercalcemia
Stones

7. RDA
A 600 microg
D 200 IU
E
K
600 microg
800
200 IU
400 IU
10 mg
10 mg
8 mg
120 microg 90 microg