VITAMIN A

 

“Vitamin A” covers both a pre-formed vitamin, retinol, and a pro- vitamin, beta carotene, some of which is converted to retinol in the intestinal mucosa.

FUNCTIONS:-

Vitamin A participates in many bodily functions :

(a)   It is indispensable for normal vision. It contributes to the production of retinal pigments which are needed for vision in dim light.

 

(b) It is necessary for maintaining the integrity and the normal functioning of glandular and epithelial tissue which lines intestinal, respiratory and urinary tracts as well as the skin and eyes.

 

(c) It supports growth skeletal growth.

 

(d) Immune epithelial cancers.

 

SOURCES:-

Liver, eggs, butter, cheese, whole milk, fish and meat, vegetables spinach and amaranth green and yellow fruits and vegetables (papaya, mango, pumpkin) vanaspathi , margarine, milk) can be an important source.

The liver has an enormous capacity for storing vitamin A. Under normal conditions, a well-fed person has sufficient vitamin A reserves to meet his needs for 6 to 9 months or more.

 

DEFICIENCY:-

The signs of vitamin A deficiency are predominantly ocular. They include night blindness, conjunctival xerosis, Bitot’s spots, corneal xerosis and keratomalacia. The term “exophthalmia” (dry eye) comprises all the ocular manifestations of vitamin A deficiency ranging from night blindness to keratomalacia, given below is a short description of the ocular manifestations.

 

(a)        Night blindness:- 

Lack of vitamin A, first causes night blindness or inability to see in dim light. The mother herself can detect this condition when her child cannot see in late evenings or find her in a darkened room. Night blindness is due to impairment in dark adaptation. Unless vitamin A intake is increased, the condition may get worse, especially when children also suffer from diarrhea and other infections.

 

(b)       Conjunctival xerosis:-

This is the first clinical sign of vitamin A deficiency. The conjunctiva becomes dry and non-wettable.  Instead of looking smooth and shiny, it appears muddy and wrinkled. It has  been well described as  “emerging like sand banks at receding tide” when the child ceases to cry .

 

(c)        Bitot’s spots:-

Bitot’s spots are triangular, pearly-white or yellowish, foamy spots on the bulbar conjunctiva on either side of the cornea. They are frequently bilateral. Bitot’s spots in young children usually indicate vitamin A deficiency. In older individuals, these spots are often inactive sequelae of earlier desease.

 

(d)       Corneal xerosis:-

This stage is particularly serious. The cornea appears dull, dry and non-wettable and eventually opaque. It does not have a moist appearance. In more severe deficiency there may be corneal ulceration. The ulcer may heal leaving a corneal scar which can affect vision.

 

(e)        Keratomalacia:-

Keratomalacia or liquefaction of the cornea is a grave medical emergency. The cornea (a part or the whole) may become soft and may burst open. The process is a rapid one. If the eye collapses, vision is lost. Keratomalacia is one of the major causes of blindness in India and frequently associated with protein energy malnutrition.

 

EXTRA-OCULAR MANIFESTATIONS:-

These comprise follicular hyperkeratosis, anorexia and growth retardation which have long been recognized. They are non-specific and difficult to quantify. Recent studies seem to indicate that even mild vitamin A deficiency causes an increase in morbidity and mortality due to respiratory and intestinal infection.

 

PREVENTION:-

Since vitamin A can be stored in the body for 6 to 9 months and liberated slowly, a short term, simple technology had been evolved by the national institute of nutrition at Hyderabad (India) for community based intervention against nutritional blindness, which has subsequently been adopted by other countries (31). The strategy is to administer a single massive dose of 200,000 IU of vitamin A  in oil (retinol palmitate) orally every 6 months to preschool children (1 year to 6 years), and half that dose (100,000 IU) to children between be, as it were “immunized” against exophthalmia. The protection afforded by six-monthly dosing seems very adequate as measured by clinical signs of deficiency (32). In a longitudinal study in Hyderabad city, the incidence of keratomalacia in areas covered by the programme decreased by about 80 per cent (33).

 

ASSESSMENT OF VITAMIN A DEFICIENCY:-

The formulation of an effective intervention programme for prevention of vitamin A deficiency begins with the characterization of the problem. This is done by population surveys employing both clinical and biochemical criteria. These surveys (prevalence surveys) are done on preschool children (6 months to 6 years) who are at special risk. The criteria recommended by who (24) are given in table 5. The presence of any one of the criteria should be considered as evidence of exophthalmia problem in the community.

 

RECOMMENDED ALLOWANCES:-

The recommended daily intake of vitamin A is 750 micrograms for adults. The detailed recommendations are given in table 6.

Daily intake of vitamin A recommended by ICMR

 

Infants

0 to 6 months                                400

6 to 12 months                             300

Children

1 to 3 years                                   250

4 to 6 years                                  300

7 to 9 years                                  400

10 to 12 years                               600

Adolescents

13 to 15 years                         750

16 to 19 years                         750

 

TOXICITY:-

An excess intake of retinol causes nausea, vomiting , anorexia, and sleep disorders followed by skin desquamation and then an enlarged liver and papillar oedema