This document discusses vitamin A, including its recommended daily allowances, dietary sources, active forms, role in vision and the visual cycle, and deficiency manifestations. The RDA of vitamin A is 400-600 μg/day for children, 750-1000 μg/day for men, and 750 μg/day for women and 1000 μg/day during pregnancy. Animal sources like milk, liver, and fish liver oils as well as carotenoid-containing vegetables like carrots are good sources. Deficiency can cause night blindness, Bitot's spots, dry eyes, corneal softening and blindness as well as skin and immune system issues.

1. •Dr. Jaswant Kaur
Assistant professor
Department Biochemistry

6. Daily requirement of Vitamin A
The recommended daily allowance (RDA) of
Vitamin A for children = 400–600 μg/day, for
men = 750–1000 μg/day,
• For women = 750 μg/day pregnancy = 1000
μg/day.
• quirement of Vitamin A

7. Dietary Sources
• Animal sources :- milk, butter, cream, cheese,
egg yolk and liver. Fish liver oils (cod liver oil
and shark liver oil)
• Vegetable sources contain the yellow pigment
beta carotene.
• Carrot contains significant quantity of beta
carotene. Papaya, mango, pumpkins and
green leafy vegetables (spinach, amaranth) are
other good sources of vitamin A activity.

8. Active form of viatmin A

9. Interconversion of vitamin A molecules.

10. Vitamin A metabolism.

11. Wald’s visual cycle

12. Mechanism of Dark Adaption

13. Dark adaption mechanism
• Person shifts from bright light to dim area- leads
difficulty in seeing .
Due to resynthesis of rhodopsin & vision is
improved.
• Increased in Vit. A deficiency.
• Red light bleaches rhodopsin to a lesser extent.
photosensitive cells
• Rods cones
( for dim light vision) ( bright light & color vision)

14. • Vision
• Visual cycle
• Rods are for Vision in Dim Light
• Cones are for Color Vision
• Other Biochemical Functions
• Gene Regulation
• Immunological System
• Reproductive System
• Anti-oxidant Property
• Effect on Skin

15. Cont.

16. Deficiency manifestation of Vit. A
• Night Blindness or Nyctalopia
• Bitot’s Spots
• Xerophthalmia
• Keratomalacia
• Preventable Blindness
• Skin and Mucous Membrane Lesions growth retardation
reduced immunity against infections.

17. • Deficiency of vitamin A: Deficiency leads to a variety of
disorders of the eyes and this affect the vision, some of the
disorders are –
• 1)Night blindness: The person cannot see the objects in
dim light and in nights.
• Bitot’s spot:- seen as greenish white triangular
plaques adherent to conjuctiva.
2)Xeropthalmia : conjuctiva becomes dry, thick, wrinkled.
• Losses its transperancy.
• Dryness spreads to cornea.
3) Keratomalacia ( softening of the cornea) :- Xeropthalmia
persists for long time , leads Keratomalacia .
Occur degeneration of corneal epithelium

18. Bitot spots
Keratomalacia.

19. • 4)Skin become scaly, rough and is covered
with papillae (Small eruptions).
• 5)Reproductive functions may also be
effected in vitamin ‘A’ deficiency.
• National Institute of Nutrition, Hyderabad
has evolved a method giving a large dose
(5 – 6 drops) of Vitamin-A once in six
months to prevent blindness in children

20. Hypervitaminosis A or toxicity
• Excessive intake can lead to toxicity since the
vitamin is stored.
• Symptoms of toxicity are anorexia, irritability,
headache, drowsiness and vomiting, increased
intracranial tension.
• Sometimes swelling over long bones (bony
exostosis) may occur with painful bones.
Enlargement of liver is also seen in children

21. Objectives
• List the different active forms of vitamin A
State the dietary sources and RDA in children,
adults, pregnancy and lactation
• Explain the role of vitamin A in vision and
Wald’s visual cycle
• Describe the deficiency manifestations of
vitamin A .