Vitamin A Deficiency

Write sources, daily requirement, functions, and deficiency manifestation of vitamin A.
Answer.

Introduction Of Vitamin A

Vitamin A exists in three forms
- Vitamin A alcohol – retinol
- Vitamin A acid – retinoic acid
- Vitamin A aldehyde – retinal
Vitamin A can also be formed from provitamins, known as carotenes

Daily Requirement

4000 to 5000 IU

1 IU = 0.3 micrograms of retinol

Dietary Sources

Animal sources – liver, kidney, egg yolk, milk, cheese, butter and cod liver oil
Vegetable sources – carotenes – carrots, spinach, pumpkins, mango and papaya

Functions Of Vitamin A

Role In Vision is main function of vitamin A

Vitamin A is required for normal reproduction
Vitamin A is required for epithelialization and is essential to maintain healthy epithelial tissue.
Vitamin A is required for the construction of normal bone and teeth
Vitamin A is required for glycoprotein synthesis
Vitamin A is required for the synthesis of chondroitin sulfate
Vitamin A plays a role in cell differentiation and cell division
Vitamin A is involved in protein synthesis
Vitamin A plays a role in DNA metabolism
Carotenes function as antioxidants and reduce the risk of cancers initiated by free radicals

Vitamin A Deficiency

Retinol deficiency depresses the re-synthesis of rhodopsin and interferes with the function of rods resulting in night blindness
In Vitamin A deficiency sperm cells do not mature and in females there may be abortion.
In Vitamin A deficiency the skin becomes dry, scaly and rough. These changes are called keratinisation.
There is dryness of the conjunctiva and cornea, which is known as xerophthalmia.
White opaque spots, known as Bitots spots appear on the conjunctiva.
Cornea becomes keratinized, opaque, soft and ulcerated. This is known as keratomalacia.
Keratinization occurs in the mucous membrane of the respiratory tract leading to increased susceptibility to infection and lowered resistance to disease.
Vitamin A deficiency causes arrested bone development.
The teeth become unhealthy with chalky deposits on the surface.

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