Fat soluble vitamins are soluble in fats and fat solvents. They are insoluble in water. So these vitamins are used only if there is presence of fat in the body.
Functions
- Vitamin A is essential for the building and growth of all cells, especially skeletal cells. Vitamin A is also needed for proper tooth structure. It helps in the integrity of the epithelium, especially the mucous membranes, which line the eyes, mouth, alimentary canal, salivary glands, respiratory and genito-urinary tracts. In the deficiency of vitamin A the epithelial tissues of these parts are keratonised.
- Vitamin A maintains normal reproductive function in males
- Vitamin A is again essential for the maintenance of normal vision in dim light. This vitamin combines with protein to form rhodopsin or visual purple which is present in the retina. Visual purple absorbs light and is decomposed to retinene and protein. The protein and retinine are partially recombined to form rhodopsin in the dark
- Vitamin A plays an important role in maintaining the structure of myelin sheath
- Vitamin A also helps the synthesis of mucopolysaccharides
- High serum retinol levels reduce the risk of cancer. Vitamin A is also known as anti infective vitamin as it provides resistance power to the body by maintaining normal structure of the organs
Deficiency
Vitamin A deficiency in man may be due to low intake of vitamin A source or due to interference with absorption or storage of vitamin A in the body. In certain diseases proper assimilation of vitamin A is affected. Loss of vitamin A occurs in the blood during some infectious diseases.
Bitot’s spots: Grey coloured triangular spots are located in the conjunctiva in severe cases.
Bitot’s spots
Night blindness: In advanced deficiency the subjects cannot see objects in dim light. Difficulty to read in dim light is experienced.
Night blindness
Xerosis conjunctiva: The conjunctiva is dry thickened wrinkled and pigments. This is due to the keratinisation of the epithelial cells. The pigmentation gives the conjunctiva a smoky appearance
Xerosis of cornea: When dryness spreads to cornea, it takes on a dull, hazy and lustreless appearance.
Keratomalacia: When xerosis of the conjunctiva and cornea is not treated, it may develop into the condition known as ‘keratomalacia’. The corneal epithelium becomes opaque and ulceration and bacterial invasion of the cornea bring about its destruction resulting in blindness.
Keratomalacia
Phrynoderma:In vitamin A deficiency, the skin becomes rough because the epithelial tissues are affected. This condition is known as follicular keratosis or toad skin or phrynoderma.
Hypervitaminosis: If excess amount of vitamin A is consumed it shows ill effect in the body. The symptoms are drowsiness, headache, vomiting, itching, skin lesions and loss of appetite.
 Sources
Vitamin A activity is in the form of retinol and carotenoids.
Best sources of retinol – shark, halibut liver oil, sheep, goat and cow
Good source - butter, ghee, egg, all milk powders
Good sources of carotenoids - green leafy vegetables, carrot, pumpkin, papaya, jackfruit, mangoes and enriched
vanaspathi.
Requirements
Recommended Intake of Vitamin A
(Retinol Equivalents, RE, μg/ d)
| Group
|
Sub group
|
FAO/WHO 2004
|
Present Committee
|
| Retinol
|
Retinol
|
β-carotene*
|
Adult man
Adult Woman
|
600
500
|
600
|
4800
|
| Pregnant women
|
800
|
800
|
6400
|
| Lactating woman
|
850
|
950
|
7600
|
| Infants
|
0-6 m
6-12 m
|
375
400
|
350
|
---
2100
|
| Children
|
1-6 y
7-9 y
|
400/450
500
|
400
600
|
3200
4800
|
| Adolescents
|
10-17 y
|
600
|
600
|
4800
|
|
