Vitamin D is a fat-soluble vitamin that functions like a hormone and regulates calcium levels. It is obtained through sun exposure and dietary sources like fatty fish and eggs. The skin produces vitamin D from exposure to UVB rays, especially between 10am-3pm in spring/summer/fall. Sun exposure duration depends on skin pigmentation and sunscreen use. Recommended daily intake is 400-800 IU depending on age.

1. Shady Mahmoud

2.  Vitamin-D is a sterol which contains steroid nucleus. It is
a fat soluble vitamin and functions like a hormone.
 Sources of vitamin D:
1. Diet.
2. Sun exposure.

3. Vitamin D in the diet
 It occurs in two forms:
Vitamin D2 (Ergocalciferol).
Vitamin D3 (Cholecalciferol).

4.  Ergocalciferol (vitamin D2) is formed from
ergosterol and is present in plants.
 Cholecalciferol (vitamin D3) is found in animals
(fatty fish, fish liver oils, egg yolk etc).
 Milk is not a good source.
 Both the sterols are similar in structure except
that ergocalciferol has an additional methyl
group.
 They are sources for vitamin D activity and are
referred as provitamins.

5.  Absorption: vitamin D2 and D3 are absorbed
from upper small intestine and bile is essential.
 Mechanism: vitamin D3 and D2 form mixed
micelles by combining with bile salts (micelles).

7.  During the course of cholesterol biosynthesis 7-
dehydrocholesterol is formed as an
intermediate.
 On exposure to sunlight, 7-dehydrocholesterol is
converted to cholecalciferol in the skin (dermis
and epidermis).
Sun exposure

8.  The production of vitamin D in the skin is
directly proportional to the exposure to
sunlight and inversely proportional to the
pigmentation of skin.
 Excessive exposure to sunlight does not result in
vitamin D toxicity since excess provitamin D3
are destroyed by sunlight itself.

10. Transport:
 Vitamin D is transported from intestine to the liver
by binding to vitamin D binding globulin.
 25 OH D3 and 1,25 OH2 D3 are also transported
in the blood by binding to it.
Storage:
 25 OH cholecalciferol is the major storage and
circulatory form of vitamin D.

11. Activation of Vitamin D:
 Active form: the active form of vitamin D is 1,25
OH cholecalciferol and is also called as
calcitriol.
 Cholecalciferol is first hydroxylated at 25th
position to 25 OH cholecalciferol by a specific
hydroxylase present in liver.
 Kidney possesses a specific enzyme, 25 OH
cholecalciferol 1 α hydroxylase.

12.  1 α hydroxylase hydroxylates 25 OH
cholecalciferol at position 1 to produce 1,25 –
OH cholecalciferol (calcitriol).
 Both hydroxylase enzymes (of liver and kidney)
require cytochrome P450, NADPH and molecular
oxygen for hydroxylation process

13. Regulation
 Formation of 1,25 – DHCC is regulated by the
regulation of renal 1 α – hydroxylase.
 1 α – hydroxylase activity is increased by
hypocalcemia.
 Hypocalcemia stimulates PTH secretion which,
in turn, increases 1 α – hydroxylase.
 1 α – hydroxylase activity may be feedback
inhibited by 1,25 – DHCC

14. Function
 Vitamin D regulates the plasma levels of calcium and
phosphorous.
 Plasma calcium levels are regulated by effects of 1,25 –
DHCC on small intestine, kidney, and bone.
 It maintains the plasma calcium levels by increasing
absorption of calcium from small intestine, increasing
reabsorption of calcium by renal distal tubules and
increasing mobilization of calcium from bone

15.  24,25 – DHCC is another metabolite of vitamin D
 It is synthesized in kidney by 24 - hydroxylase
 If Calcitriol concentration is adequate, 24 –
hydroxylase acts leading to the synthesis of a
less important compound 24,25 – DHCC
 To maintain calcium homeostasis, synthesis of
24,25 – DHCC is important

16. Recommmended daily intake
 Children - 10 gm/day or 400 IU/day
 Adults - 5 gm/day or 200 IU/day
 Pregnency, lactation -10 gm/day or 400 IU/day
 Above the age of 60 yrs - 600 IU /day

18. Decal B 12 120 ml syrup
 Each 5 ml syrup contains:
Ca 50 mg
Vitamin D3 1000 IU
Vitamin B12 10 mcg
 Dose: 1 teaspoonful

19. Vidrop 2000 IU/ml
 Each drop contains 100 IU of
vitamin D3 (cholecalciferol)
 1 ml =28 drops
 Dose: 5000 IU daily for 3
weeks.

20. Devarol-S 200000 IU ampoule
 Each 2 ml contains:
Vitamin D3 (Cholecalciferol)
5 mg (equivalent to 200000
I.U.).
 Dose: 1 ampoule every 6
months.

21. Sterogyl 2,000,000 ul/100 ml
 Each drop contains 400 IU of
vitamin D2 (ergocalciferol).
 1 ml = 50 drops.
 Dose: 2 – 5 drops daily
provide 1000-2000 IU.

22. Alfacareno 10 ml drops
 It contains alphacalcidol (1
OH cholecalciferol).
 Used especially in renal
rickets.
 Dose: < 20 kg: ½ the weight
drops daily.
 > 20 kg: the weight drops
daily.

24. Shady Mahmoud

25.  The part of the sun’s rays that is important is
ultraviolet B (UVB). This is the most natural way to
get vitamin D.

26.  Duration of exposure.
 Type of the skin.
 The amount of exposed skin.
 Sunscreen use.
 Age: elderly produce less vitamin D.
 Altitude: higher altitude produce more vitamin D
 Cloud weather.
 Air pollution: Polluted air soaks up UVB or reflects it
back into space.
 Being behind glass: glass blocks all UVB.

27.  Sunlight exposure typically between 10 am and 3 pm
in the spring, summer, and fall.
 When the sun’s rays enter the Earth’s atmosphere at
too much of an angle, the atmosphere blocks the UVB
part of the rays, so the skin can’t produce vitamin D.
This happens during the early and later parts of the
day and during most of the day during the winter
season.

28.  Exposing the skin for a short time will make all the
vitamin D can produce in one day.
 The body can produce 10,000 to 25,000 IU of vitamin
D in just the time it takes for the skin to turn pink
(could be just 15 min. in fair skinned people).

29.  Infants and children should be kept out of direct
strong sunlight (spend time in the shade).
 As Infants have delicate skin which burns more easily,
the American Academy of Pediatrics recommends that
babies under six months old should stay out of the
sun completely.

30.  Pregnants: In two recent studies from the University
of South Carolina, they found that pregnant women
need to take 4,000 IU of vitamin D everyday to make
sure that their newborn child has enough when he is
born.
 Lactation :the Vitamin D Council recommends that:
a) If she takes a supplement of 6,000 IU of vitamin D
each day, she shouldn’t need to give her baby any
vitamin D supplement.
b) If she is not taking a supplement or getting a good
amount of sun exposure, or if she is taking less than
5,000 IU/day of vitamin D, the baby should be given a
vitamin D supplement.

31.  Infants (<1 year): 400 IU / day
 Children and adults: 600 IU / day
 Elderly (> 70 years): 8oo IU / day
 Reference: Institute of Medicine, Food and Nutrition Board. Dietary
Reference Intakes for Calcium and Vitamin D. Washington, DC:
National Academy Press, 2010.