Vitamin A is a fat-soluble vitamin that is important for vision, cell growth and differentiation, immunity, and reproduction. It exists in preformed and provitamin A carotenoid forms. Beta-carotene from plants is cleaved to form retinal in the intestine which is then converted to retinol and stored in the liver. Deficiency can cause night blindness, dry eyes, susceptibility to infections, and even blindness. Adequate vitamin A is important for vision, immune function, cell growth and reproduction.

1. OPTOM FASLU MUHAMMEDOPTOM FASLU MUHAMMED

2. CHEMISTRY OF VITAMIN A
• VITAMIN A is fat soluble vitamin
• Pro-Vitamin Beta-Carotene present in plant tissues give
rise two molecules of Vitamin A.
• All compounds with Vitamin A activity is called retinods.
• Retinol (alcohol) Retinal (aldehyde) & Retinoic acid
(Vitamin A acid)
• Retinal on reduction gives Retinol & on oxidation
Retoinic acid.
• Vitamin A1 – all trans variety of retinal is most common
• Vitamin A2 – found in fish oils.
• Biologically important compounds is 11 Cis – Retinal.

3.  Intestine is the major site
 Cleavage of Beta Carotene by di-
oxygenase results in the formation of
retinal.
 Intestine retinal is reduced to retinol.
 Absorption requires fat & Bile salts.
 It is transported to the liver and stored as
retinal Palmitate.

4. Conversion of Carotenoids to
Retinoids
• Enzymatic conversion of
carotenoids occurs in liver
or intestinal cells, forming
retinal and retinoic acid
• Provitamin A carotenoids
– Beta-carotene
– Alpha carotene
– Beta-cryptoxanthin
• Other carotenoids
– Lutein
– Lycopene
– Zeaxanthin

5. Absorption of Vitamin A
• Retinoids
– Retinyl esters broken down to free retinol in
small intestine - requires bile, digestive
enzymes, integration into micelles
– Once absorbed, retinyl esters reformed in
intestinal cells
– 90% of retinoids can be absorbed
• Carotenoids
– Absorbed intact, absorption rate much lower
– Intestinal cells can convert carotenoids to
retinoids

6. Transport and Storage of Vitamin A
• Liver stores 90% of vitamin A in the body
• Reserve is adequate for several months
• Transported via chylomicrons from intestinal
cells to the liver
• Transported from the liver to target tissue as
retinol via retinol-binding protein.
• Retinol- RBP Complex binds to specific
receptors on retina, skin,gonads & other
tissues.

7. Vitamin A in Foods
• Preformed
– Liver, fish oils, fortified milk,
eggs, cheese, yolk other fortified foods
– Fish liver oils (shark and code liver oil)
– Contributes ~70% of vitamin A intake for
• Provitamin A carotenoids
– green leafyvegetables , yellow-orange /fruits
– Carrot, papaya, mango, Pumpkins.

8. NORMAL CONCENTRATION IN BLOOD
&
RECOMMENDED DAILY ALLOWANCE
• 0.15 to 0.6 mg/dl
• Children (400-600) microgram/day
• Men-(750-1000) microgram/day
• Women -750 microgram/day
• Pregnancy- 1000 microgram/day
• Lactation - 1200µg/day

9. Functions of Vitamin A: Vision
• Retinal turns visual light into nerve signals
in retina of eye
• Retinoic acid required for structural
components of eye
– Cones in the retina
• Responsible for vision under bright lights
• Translate objects to color vision
– Rods in the retina
• Responsible for vision in dim lights
• Translate objects to black and white vision

10. Functions of Vitamin A:
Growth and Differentiation of Cells
• Retinoic acid is necessary for cellular
differentiation
• Retinol is Important for embryo
development, gene expression.
• Retinoic acid influences production,
structure, and function of epithelial cells
that line the outside (skin) and external
passages (mucus forming cells) within the
body

11. The Visual Cycle

12.  During Bright light Entire Rhodopsin is
found to be in bleached condition and
when the person moves in to dark area it
takes a few seconds to resynthesize the
rhodospin to activate the Rod cells to
restore vision in the Dim light.
 This time interval is called Dark
adaptation time and it is found to be high
in Vitamin A deficiency.

13. Functions of Vitamin A:
Immunity
• Deficiency leads to decreased resistance
to infections
• Supplementation may decrease severity of
infections in deficient person

14.  Vitamin A can act as antioxidant
 Due to the antioxidant property it can
exhibit anticancer activity.
 Effect of vitamin A is complementary to
VitaminE
 Beta Carotene Prevents cancer
 Retinol can act as steroid hormone
controlling the expression of genes
 Retinoic acid is found to have important
role in Glycoprotein synthesis.

15. Terminal Ends of Retinoids

16. Deficiency of Vitamin A
• Most susceptible
populations:
– Preschool children
with low F&V intake
– Urban poor
– Older adults
– Alcoholism
– Liver disease (limits
storage)
– Fat malabsorption
• Consequences:
– Night blindness
– Decreased mucus
production
– Decreased immunity
– Bacterial invasion of
the eye
– Conjunctival xerosis
– Bitot’s spots
– Xerophthalmia
– Irreversible blindness
– Follicular
hyperkeratosis
– Poor growth

17.  Nyctalopia;-Night Blindness
 Xeropthalmia;- conjuctiva become thick
and wrinkled. Conjuctiva become
keratinised.
 Bitot’s Spot:- Greyish Traingular spots
adherent to Conjuctiva.reversed if proper
supply of Vitamin A maintained.
 Keratomalacia;-Softening of the cornea.
 Corneal epithelium gets degenerated
and vascularised.

18.  Hyperkeratinisation of respiratory,
gastrointestinal tract and urinary tract.
 Epithelium atrophied, Urinary Calculi.
 Generalised infections observed in
skin.

19. Health Effects of Vitamin A