Vitamin A is a fat-soluble vitamin that exists in three major forms: retinal, retinol, and retinoic acid. It plays an important role in vision, cell growth, reproduction, and maintaining epithelial tissues. Vitamin A was first used to treat night blindness in 500 BC and its chemical structure was described in 1931. It is obtained through diet from animal sources such as liver, milk, and eggs or plant sources like carrots and sweet potatoes. A deficiency can cause vision problems and impact growth and reproduction, while too much can be toxic.

1. FAT SOLUBLE VITAMIN- A
Laxman I
1ST MSc BIOTECH

2. Vitamins
• Vitamins are the organic compounds
required in the diet in small amounts in
different natural foods
• Necessary for the growth and maintenance
of good health.
• Daily requirement depends on the age group
and increase during growth, pregnancy and
lactation.

3. “A Vitamin is a substance that makes
you ill if you don’t eat it”
-Albert Szent-Gyorgyi, Nobel Prize winner, 1937

4. CLASSIFICATION OF VITAMINS:
• There are about 15 vitamins, essential for humans

5. VITAMINS
CHARACTERISTICS FAT SOLUBLE
VITAMINS
WATER SOLUBLE
VITAMINS
1 Solubility Fat soluble Water soluble
2 Absorption Bile salts are
required
Simple intestinal
absorption
3 Transportation Transported by
carrier protein
No protein is
required, travels
freely
4 Storage In liver and fat
tissues
Not stored
5 Excretion Surplus vitamins
are stored
Surplus vitamins are
detected and
removed in urine
6 Requirement Required in
periodic doses
Required in frequent
doses

6. VITAMIN- A
•Vitamin A is an essential micronutrient for humans, meaning
that it cannot be biosynthesized in the body and thus must be
obtained from dietary sources.
•Vitamin A is a collective name for a group of lipophilic
biomolecules required by humans to perform different vital
metabolic functions like vision, repair, reproduction, growth
and tissue differentiation.
•The vitamin exists in three Major forms: retinal, retinol and
retinoic acid.

7. HISTORY
• It is recorded in history that Hippocrates cured night blindness(about 500 b.c)
• He prescribed to the patients ox liver(in honey)which is now known to contain
high quantity of vitamin a.
•
• By 1917, Elmer McCollum et al,. at the university of Wisconsin-Madison,
studied the role of fats in the diet and discovered few accessory factors. These
“accessory factors” were termed “fat soluble” in 1918 and later “vitamin A” in
1920.
• In 1919, Harry Steenbock (University of Wisconsin) proposed a relationship
between yellow plant pigments (beta-carotene) and vitamin A.
• In 1931, Swiss chemist Paul karrer described the chemical structure of vitamin
A.
• Vitamin A was first synthesized in 1947 by two Dutch chemists, David Adriaan
van Dorp and Jozef Ferdinand Arens.

8. Chemistry:
• Vitamin A is fat soluble. The active form is present
only in animal tissues.
• The provitamin, beta-carotene is present in plant
tissues.
Three different compounds with vitamin A activity
1. Retinol (vitamin-A alcohol )

9. 2. Retinal (vitamin-A aldehyde)
3. Retinoic acid (vitamin-A acid)

10. WALDS VISUAL CYCLE
• The term Visual cycle was coined by George Wald in the
mid 1900’s
• To describe the ability of eye to “re-cycle” Vitamin A for the
synthesis of visual pigments
• Wald was awarded Nobel prize in 1967 for identifying role
off Vitamin A in vision.
• Process of visual information begins in the retina with the
detection of light by photoreceptor cells.
• Photoreceptors involved in the vision are rods and cones.
• Rhodopsin (mol.wt 35,000) is a membrane protein present
in the photoreceptor rod cells of retina.

11. WALDS VISUAL CYCLE

12. BIOLOGICAL FUNCTIONS OF
VITAMIN-A
• They regulate protein synthesis.
• Function as steroid hormones.
• To maintain healthy epithelial tissue
• Involved in the cell growth
• Required to prevent keratin synthesis
• Necessary for normal reproduction

13. BIOLOGICAL FUNCTIONS OF
VITAMIN-A
• Maintenance of proper immune system to
fight against various infections.
• Cholesterol synthesis
• Function as antioxidants

14. Recommended dietary
allowance (RDA)
 The daily requirement of vitamin A is expressed as retinol
equivalents (RE) rather than International Units (IU).
 The recommended daily allowance (RDA) for
• Children = 400–600 mcg/day • Men = 750–1000 mcg/day
• Women = 750 mcg/day • Pregnancy = 1000 mcg/day
 One international unit = 0.3 mcg of retinol.
 One retinol equivalent = 1 ug of retinol or 6 ug of beta
carotene.

15. SOURCES
Plant sources: sweet potatoes, carrots, pumpkins,
papayas, tomatoes and leafy green vegetables
which supply pro vitamin A (carotene) in the diet.
Cereals also contain carotene.
Animal sources: Preformed vitamin A (retinol) is
supplied by foods of animal origin; they are liver,
milk, butter, eggs. Kidney, the fat of muscle, meats,
and fish. Liver oil which is very rich in the vitamin.

16. VITAMIN ‘A’ DEFICIENCY
The vitamin A deficiency may be due to
inadequate dietary intake, impaired intestinal
absorption, reduced storage in liver and chronic
alcoholism.
• Effect on eyes: leads to xerophthalmia
• Effect on growth
• Effect on reproduction
• Effect on skin and epithelial cells

17. Hypervitaminosis A
Excessive consumption of vitamin A leads to toxicity
The symptoms of hypervitaminosis A
• Dermatitis raised intracranial tension
• Enlargement of liver
• Skeletal decalcification
• Tenderness of long bones
• Loss of weight
• Irritability
• Loss of hair
• Joint pains

18. References
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