VITAMIN A DEFICIENY AND

ITS IMMUNE RESPONSE

Submitted by T.Tamil selvan .

INTRODUCTION : The ancient Egyptians as mentioned in the “PAPYRUS EBERS” that juice obtained from cooked liver should be applied to eye to cure eye diseases mostly night blindness.

Vitamin A activity of carotenoids was discovered by Stunbock -1919.

Structure of vitamin A was determined by Karrer - 1931.

Synthesis in lab by Kuhn and Morris – 1937.

Due to its role in visual process it is often called as “Antixerophthalmic factor” or “Bright eyes ” vitamin .

Properties :

Retinol is a Viscid , colorless oil. It is soluble in fat and fat solvents ,but

insoluble in water. It is destroyed on exposure to UV light.

Vitamin A is found in two forms A1 and A2. Carotenoids are the precursors of Vitamin A. Carotenoids that give rise to vitamin A in

animal body is called as provitamin A. Beta-carotene is the most potent of all those

forms. Vitamin A1 is a complex primary alcohol

called Retinol .

DEFICIENCY SYMPTOMS : Prolonged deficiency of vitamin A may result in

Inflammation of the eye , Poor vision and night blindness.

There is an increased susceptibility of infections especially of the respiratory tract in the form of frequent and common colds .

Vitamin A deficiency leads to lack of appetite , defective gums and tooth , skin disorders such as pimples , acne , boils and premature wrinkles.

It include retorted growth in children , dry and dull hair , dandruff , Exclusive hair loss , ridged nails and poor sense of taste and smell .

Vitamin A is an important factor in Tooth formation. In its deficiency there is a defective formation of enamel so that the dentin is exposed. So that sound tooth formation does not occur.

The symptoms of vitamin A are not immediate .

DEFICIENCY MANIFESTATION OF EYES :

NYCTOLOPIA : one of the earliest symptoms of vitamin A

deficiency . The individuals have difficult to see in Dim

light. Since the dark adoption time is increased. Prolonged deficiency irreversibly damages

a number of visual cells.

xerophthalmia : Severe deficiency causes xerophthalmia . This causes dryness in conjunctiva and

cornea and keratinization of epithelial cells .In certain areas of conjunctiva while triangular plaques known as Bitot’s spots are seen.

Keratomalacia : kerata = hair ; malakia = softness . It is a corneal disease . occurs maximally in pre – school children

of age 3-4 years. It suddenly happens in young children with

kwashiorkor . At first the cornea loses its luster ,

undergoes necrosis and later to form a large , white ulcerative area .

In case of extensive ulceration the whole eyeball may shrink .

Phrynoderma : It is a skin lesion caused by hyperkeratosis . The skin on the outer aspects of forearms in

the regions of the elbows and the thighs and become rough and spiky.

In the alimentary tract , the deficiency of vitamin A causes damage to the Intestinal mucosa , resulting in diahorrea .

Hypervitaminosis A : Excessive consumption of vitamin A leads

to toxicity .

The symptoms include dermatitis , enlargement of liver , skeletal decalcification , loss of weight , irritability , loss of hair .

The subject have constant head ache , due to intercranial pressure which resembles the symptoms of brain tumor.

Ingestion of high quantities of vitamin A by pregnant women is associated with the risk of congenital malfunction in the developing fetus.

Effect on growth : It results in growth retardation due to impairment in skeletal deformation .

Effect on Reproduction : The reproductive system is adversely affected in vitamin A deficiency. Degeneration of germinal epithelial cells leads to Sterility in males .

Effect on skin : The skin becomes rough and dry. Vitamin A deficiency is associated with formation

of urinary stones . Keratinization of epithelial cells of Gastro -

intestinal tract , urinary tract , respiratory tract is noticed .

This leads to increased bacterial infection .

Vitamin A and vision : The biochemical function of vitamin A in the

process of vision was first explained by George Wald ( Noble prize 1968 ) .

The process is known as Rhodopsin cycle or Wald’s visual cycle .

The retina of Human eye posses two types of cells – Rods and Cones. ( Rhodopsin and Photopsin ) .

RODS CONES

10 million rods are present. 5 million cones are

present.

Rods present in periphery.

Cones at the center of retina.

Involve in dim light vision.

Involves in bright light vision.

Chemical cycle : Beta – carotene.

Retinol opsin ( Visual )

Retinal Retinyl phosphate

Retinoic acid

Retinoid - Includes natural and synthetic forms of vitamin A.Rich dietary sources : Animal origin : sheep liver , egg yolk , whole milk , butter and ghee. Liver oils of various fishes are rich in vitamin A. Vegetables : beet , carrot , spinach etc.. contain lot of carotene . Fruits : Mangoes , apricots , oranges , etc.

Dietary requirements : Infants - 350 -500 µg 1-6 yrs. - 400 µg 7-12 yrs. - 500 µg Adults - 600 µg Men - 600 - 900 µg Women - 600 - 900 µg Pregnant - 700 - 800 µg Lactating - 1100 – 1300 µg

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