This document discusses vitamin D, including what it is, how the body processes and activates it, its functions, sources, and requirements. Vitamin D is a fat-soluble vitamin synthesized in the skin upon exposure to sunlight and found in some foods. It is activated through two hydroxylation steps in the liver and kidneys. Vitamin D promotes calcium absorption and bone mineralization and supports immune function. While sunlight is the major source, many factors impact skin synthesis, so dietary sources and supplements are also important to meet daily requirements.

1. Vitamin D
By
Dr. Rania S. Seoudi
Video link
https://youtu.be/CYj2G7XiQtg

2. What is Vitamin D?
• Vitamin D is a fat-soluble vitamin that
ultraviolet rays (UVB) coming from the
sunlight triggers its synthesis in the skin, it
is also found in few foods.

3. Non-active form of vitamin D:
• Provitamin D (7-dehydrocholesterol, 7-DHC)
converts into Previtamin D (7-dehydrocholesterol,
7-DHC) when exposed to UVB.
• Both Provitamin D and Previtamin D are
non-active forms of vitamin D.

4. Activation of vitamin D:
• The previtamin D is unstable molecule, it
isomerizes by body heat into D3 that
transported to the liver, where the activation
process starts.
• In the liver, hydroxylation of D3 to 25-
hydroxyvitamin D.

5. Second hydroxylation:
• In the kidney, the second hydroxylation occurs to
convert 25(OH)D to 1,25-dihydroxyvitamin D
[(1,25(OH)2D)].
• The [(1,25(OH)2D)] formation is regulated by the
parathyroid hormone (PTH).

6. What does Vitamin D do?
• Vitamin D is found in all body cells; it has this ability to
promote the absorption of calcium and phosphate in the
body, it regulates body mineralization, prevent
hypocalcemic tetany (imbalance in electrolytes as a result
of calcium deficiency), and it stimulates innate immunity
and regulates inflammatory responses.
• Even in muscles, vitamin D has a role in cell growth and
neuromuscular function.

7. What are the sources of vitamin D?
• Only a few foods contain vitamin D.
• One major source is fatty fish such as; codfish,
salmon, tuna, shrimp, herring, and sardines.
• Other foods that contain a very little percentage of
vitamin D; are milk, egg yolk, and mushrooms. There
are some fortified foods with vitamin D such as;
some milk brands, orange juice, cereal, and
oatmeal.

8. The main source for vitamin D is the sun, so
why not taking enough of the sun?
• You probably remember your grandmother saying, babies should
be exposed to the sun for a couple of hours every week for
babies not to have rickets (a disease that causes softening in the
bone).
• The sun is the main source of vitamin D. UVB triggers the
synthesis of inactive vitamin D in the skin. The problem is that
UV is reduced to 50% by cloud cover during winter, and 60% of
UVB is reduced by smog and pollution, where sunscreen and
glass prevent UVB from penetrating to the skin.

9. Skin Melanin pigment affects amount of UVB
can penetrate skin:
• Another factor that affects the ability of the skin to synthesis
vitamin D from the sun is the amount of melanin pigment. Still,
till now, there is no clear relation between lower level of 25(OH)D
in dark skin people and any health problems.
• The Darker skin has a lower level of 25(OH)D than Caucasians skin
due to high pigment concentration, yet, dark skins have a lower
rate of fractures and osteoporosis compared with Caucasians.
• It is suggested that, probably darker skin people met their need
for vitamin D through their diet habits.

10. Sun rays and skin cancer:
• In general, vitamin D requirements hard to be
met by exposing the body to the direct sun due
to the risk of skin cancer. UV-radiation is
responsible for annual 1.5million skin cancer,
American Academy of Dermatology (AAD)
strongly advise applying sunscreen whenever
exposed to the sun to avoid any health
complications.

11. How much enough of vitamin D?
• The recommended allowed dietary allowance of
vitamin D depends on the age and the gender, the
amount based on a minimal amount of ranges
between 400 and 800 IU.

12. How long you need to be exposed to the sun?
• For the skin to benefit from the sun, the skin has to be
exposed directly to sun rays between 10 am and 3 pm.
• Face, arms, legs or back have to be exposed at least
from 5 -30 mints twice per week for the skin to
synthesize sufficient amount of vitamin D.
• Season, time of day, smog, sunscreen and time of
exposure, all are factors that affect the vitamin D
synthesis in the skin.

13. Vitamin D adequate amount in the body:
• The lower intake causes vitamin D deficiency. 25(OH)D is measured to
assess vitamin status. A blood sample is compared against serum of
25(OH)D. Recently, reference serum 25(OH)D is used for more accurate
results.
• Serum concentration recorded less than 12ng/ml (nanogram per
milliliter) is associated with critical vitamin D deficiency which results
in rickets in infants and osteomalacia in adults.
• The amount between 12 and 20ng/ml (nanograms per milliliter) is
considered inadequate, whereas the adequate amount for healthy
bones and general health, is considered to be and between 20 and 50

14. No vitamin D overdosing from the sun or
food:
• True, there is no vitamin D intoxication due to excess
sun exposure; the excess amount of synthesized vitamin
D3 is destroyed by sunlight. Foods have a low amount of
vitamin D resulting in no intoxication effect due to a
high vitamin D diet.

15. Use supplements with precautions:
• For people who are not exposed to enough sun due to; the
type of lifestyle, religious reasons, dark skin, older adults,
obese, or fat malabsorption, they need vitamin D
supplements to meet their daily requirements of vitamin D.
• The form of vitamin D in the supplements are the two
inactive forms of vitamin D (D2 and D3), where D3 showed
to be more efficient in increasing 25(OH)D levels in the
body.

16. Vitamin D intoxication related diseases:
• The danger comes from excess
supplementary intake that causes
intoxication or hypervitaminosis D, which
results in hypercalcemia and tissue
calcification, blood vessels, renal and
cardiovascular damage, and kidney stones