Vitamin A is a fat-soluble vitamin with four forms: retinol, retinal, retinoic acid, and β-carotene. It plays a crucial role in maintaining vision, growth, reproduction, and epithelial differentiation, and is also therapeutically important in treating conditions like psoriasis and severe acne. The daily requirement for adults is measured in retinol activity equivalents, with 900 RAE for males and 700 RAE for females.

1. zVitamin A
Dr Kavindya Fernando
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2. zContents
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 Vitamin classification
 Structure of vitamin A
 Sources of vitamin A
 Absorption and transport
 Mechanism of action
 Functions & body requirement

3. zVitamin classification
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Vitamins
Water soluble Fat soluble
Non-B complex B complex
Energy - releasing Hamatopoietic Other
• Vitamin A • Vitamin D
• Vitamin E • Vitamin K
• Vitamin C
• Thiamin (B1)
• Riboflavin (B2)
• Niacin (B3)
• Folic acid
• Vitamin B12
• Pyridoxine (Vitamin B6)• Biotin
• Pantothenic
acid

4. z
Vitamin A
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5. zStructure of Vitamin A
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 Vitamin A – fat soluble vitamin
 Retinoids includes
 natural & synthetic forms of vitamin A
 that may or may not show vitamin A activity
Structure
Retinol Retinal Retinoic acid β-Carotene

6. zStructure of Vitamin A
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 Retinol
 Found in animal tissue, as retinyl ester
 Primary alcohol,
 containing a β-ionone ring,
 with an unsaturated side chain
 β-carotene
 Found in plant food
 Oxidatively cleaved in the intestine to yield two molecules of retinal
 In human this conversion is inefficient,
 Vit A activity of β-carotene is only about 1/12 that of retinol

7. zStructure of Vitamin A
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 Retinal
 Aldehyde derived from the oxidation of retinol
 Retinal and retinol can readily be interconverted
 Retinoic acid
 Acid derived from the oxidation of retinal
 Cannot be reduced in the body
Retinol Retinal Retinoic acid
Oxidation
Aldehyde Acid
Oxidation

8. zSources of Vitamin A
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 Preformed vitamin A
 Liver, kidney, cream, butter and egg yolk
 Beta carotene – precursor of vitamin A
 Yellow & dark green vegetables & fruits

9. zAbsorption and transport of vitamin A
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Retinyl esters
β-Carotene
Fatty
acids
Retinol
β carotene
Retinal
Retinol
Retinyl
esters
Hydrolysed
Enterocyte
Fatty acyl
CoA
Re-
esterification
to long chain
fatty acid
Secreted as a
component of
chylomicrons lymph
Chylomicron
remnants

10. zAbsorption and transport of vitamin A …cnt
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RBP
Retinyl
pulmitate
All-trans-Retinol
Retinol- RBP
complex
Retinol Retinol
Chylomicron
remnants
RBP

11. zMechanism of action of vitamin A
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 Eg: retinoids control
the expression of
the gene of keratin
in most epithelial
tissues of the body
Retinoic acidRetinol
oxidation
Specific
receptor proteins
Epithelial cell
Activated
retinoic acid-
receptor complex
Interact with
nuclear chromatin
To regulate retinoid-
specific RNA
synthesis
Control the
production of
specific proteins

12. z
Mechanism of action of vitamin A12
Retinoic acid
Retinol
oxidation
Epithelial cell
Plasma retinol-RBPRBP
Retinoic acid
Inactivate
receptor
Activated
receptor complex
gene
mRNA
mRNA Specific proteins
Cellular
differentiation
cytasol
nucleus

13. zFunctions of Vitamin A
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Retinyl
esters
Retinol
Carotenes
Retinal All-trans
retinoic acid
(tretinoin)
13-cis retinoic
acid
(isotretinoin)
Psoriasis Tx
Promyelocytic
leukemia tx
Severe acne
Tx
Vision GrowthReproduction
Epithelial tissue
differentiation

14. zFunctions of Vitamin A
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Retinol- RBP
complex
All- trans-Retinol
RBP
Retinal rod/cone
All- trans-retinyl
esters
11-cis Retinol
11-cis Retinal
Rhodopsin
All- trans-Retinal
Opsin
Opsin
When exposed
to light
Bleaching
reduced
esterified
isomerized
oxidized

15. zRequirement of vitamin A
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 Measured with – retinol activity equivalents (RAE)
 900 RAE daily  adult male
 700 RAE daily  adult female
 1 RAE equals to
 1 mg of retinol
 12 mg of β carotene
 24mg of other carotinoids

16. zIn Summary
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 Vitamin A is a fat soluble vitamin
 There are 4 forms of vitamin A
 Retinol, Retinal, Retinoic acid & β- carotene
 They act by controlling the production of specific proteins
 It is important in maintaining vision, growth, reproduction &
epithelial differentiation
 It has a therapeutic importance in the treatment of psoriasis,
promyelocytic leukemia and severe acne

17. z
Thank You!
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