Apart from proteins, carbohydrates and fats, there are certain other substances that are present in very small amount in food stuffs that are highly essential for growth, health and well-being.

Apart from proteins, carbohydrates and fats, there are certain other substances that are present in very small amount in food stuffs that are highly essential for growth, health and well-being. They are called as vitamins. Vitamins are organic substance, present in food in minute quantities and are important for their regulatory and protective functions. The body cannot synthesize them, and therefore they have to be provided in the diet. They differ from the ‘proximate principles’ in that they do not supply energy. Neither do they supply body-building materials, as the protein and mineral do. Their general function is to act as regulators or catalysts, assisting the body in utilizing other nutrients.

Vitamins are classified into two groups on the basis of their solubility (in fat or water) into fat-soluble and water soluble Vitamins.

Fat-Soluble Vitamins Water-Soluble Vitamins

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1. Vitamin A, D, E, K Vitamin B-Group and Vitamin-C.

Fat-Soluble Vitamin

Vitamin-A: This was the first fat-soluble Vitamin to be discovered, consisting of carbon, hydrogen and oxygen. It is a yellow crystalline substance and function in the body in several chemical forms- retinol (the alcohol), retinol (the aldehydes) and retinoic acid (the acid). Collectively these forms may be referred as vitamin-A. The ultimate source of all Vitamins-A is the carotenes, which are synthesized by plants. Animals and man convert a considerable proportion of the carotene present in the food into vitamin-A. The ‘Carotenes’ are dark-red crystalline, compounds known also as ‘Pre-vitamin-A’ or as ‘Precursors of Vitamin-A).

Functions:

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Vitamin-A performs a number of functions.

1. Vision:

Vitamin-A is related to the maintenance of normal vision in dim light. It occurs in the light receptor cells in the retina in combination with protein. This substance is known as visual purple (rhodopsin). It is bleached in the presence of light, which enables a person to see. In this process, some of the Vitamin-A is used. If more of Vitamin-A is not available, the ability of the eye to adjust to changes in the intensity of light is impair and hence suffers from night blindness or cannot see after darkness over dim light.

2. Epithelial tissues:

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Vitamin-A helps in fighting against infection by maintaining the normal vitality of the epithelial cells of the skin and the mucous membrance of the internal tissues. That is why it is called as the ‘Anti-infective’ Vitamins.

3. Growth:

Vitamin-A is essential for normal skeletal and tooth development. With a deficiency of Vitamin-A, bones do not grow in length and the normal remodeling process does not take place.

4. Reproduction:

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Vitamin-A is also essential for promoting fertility in animals. In the absence of Vitamin-A, failure of sperm-autogenesis occur in the male, and fetal desorption occur in the female.

Sources:

Vitamin-A is present in animal foods like butter, ghee, whole milk, curd, egg yolk and liver. Even liver oils of certain fish like Cod, halibut and shark are rich in this Vitamin. Vitamin-A is not present in vegetable foods, but contains carotene- the precursor of Vitamin-A which is converted to Vitamin-A in the body. Leafy vegetables such as spinach, amarnath, coriander leaves, curry leaves, drumsticks and ripe fruits like mangoes, papaya and tomatoes are rich in carotene.

Daily Allowance

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The recommended allowances for Vitamin-A are stated in retinal equivalents and international units. One I.U of Vitamin is equivalent to 0.6 micrograms of carotene. The average adult needs 5,000 I. U. while children under one year need 1,500 I.U. of vitamin-A daily. A great amount of Vitamin-A is required during the growing period, pregnancy, lactation, illness and convalescence.