vitamin D metabolism

2. It is a fat soluble vitamin.
Resembles sterols in structure and functions
like a hormone.
Synthesized by the body after exposure to UV
rays or obtained from food sources

3.  Fortified foods
Milk, cheese, yogurt, orange juice
 Ready to eat cereals
 Sun exposure
Rays from the sun trigger synthesis in the skin

4. Ergocalciferol (vitamin D2) is formed from
ergosterol and present in plants.
Cholecalciferol (vitamin D3) is found in
animals.
Ergocalciferol and cholecalciferol are sources
for vitamin D activity and are referred as
provitamins.

6. Both ergocalciferol and cholecalciferol are
similar in structure expect that ergocalciferol
has an additional methyl group and double
bond.
25 hydroxy vit D3 (calcidiol)
1,25 dihydroxy vit D3 (calcitriol).

7. Absorption
◦ Vitamin D is absorbed from the small intestine
for which bile is essential.
Distribution
◦ Stored in adipose tissue
Metabolism
◦ Transported to the liver, then kidneys, where
it is activated

8. Excreted in bile
Metabolized to water soluble metabolites
and then excreted in urine as well.

9. Calcitriol is biologically active form of
vitaminD.
It regulates the plasma levels of calcium and
phosphate.
It acts at 3 different levels:
1. Action of calcitriol on intestine.
2. Action of calcitriol on bone.
3. Action of calcitriol on kidney.

11. It is an another metabolite of vitamin D.
Synthesized in kidney by 24 hydroxylase.
Exact function is not known.
It is believed that when calcitriol
concentration is adequate 24 hydroxylase
leading to formation of less imp compound
24,25 DHCC.
In this way to maintain homeostasis of
calcium synthesis of 24,25 DHCC is also
important.

12.  Cell differentiation
inhibits proliferation and stimulates the
normal differentiation of cells
 Immunity
The inactive form of vitamin D aids in the
formation of active vitamin D which enhances
immunity and inhibits the development of
autoimmune disease.

13. Calcium balance
◦ With decreased dietary calcium, PTH is
secreted and causes increased production of
calcitriol, a hormone
◦ Calcitriol restores normal calcium levels by
increased absorption of dietary calcium,
increased mobilization of calcium from bone,
and increased reabsorption from kidneys

14. Heart disease
◦ Renin, important in regulation of blood
pressure and heart health, is associated with
vitamin D levels
Maintaining normal phosphorus levels
◦ Bone cannot be properly mineralized without
phosphorus

16. During vitamin D deficiency, calcium
absorption cannot be increased to meet
body's needs
Therefore, calcium is taken from bones
to maintain normal serum levels

17. Higher melanin content (darker skin)
Breast-fed infants
Elderly
Body covering/use of sunscreen
Fat malabsorption syndrome
Obesity
Inadequate dietary intake
Increased excretion
Genetic susceptibility

18. Rickets
Infantile tetany
Poor growth
Osteomalacia.

19. Rickets/Osteomalacia
◦ caused by lack of vitamin
D, calcium, or phosphate,
which leads to softening
and weakening of the
bones

20. THANK YOU….