VITAMIN A

VITAMIN A

Vitamin A, one of the fat-soluble vitamins (A, D, E and K) controls protein synthesis at either transcriptional or post-transcriptional level. Vitamin A refers generally to all components structurally related to retinol that have biological activity. Carotenoids are provitamin, a substance found in vegetables. Beta-carotene is the most effective precursor of vitamin A and a strong antioxidant, which prevents cellular damage.

ABSORPTION AND METABOLISM

Vitamin A is absorbed in esterified form as part of chylomicron. The yellow beta-carotene requires bile salts for absorption and is converted to vitamin A in the intestinal tract. Once absorbed, vitamin A is stored in the liver. The liver releases vitamin A to the circulation, bound to RBP. RBP takes vitamin A to the retina of eye, which is essential for vision, particularly night vision.

PHYSIOLOGIC FUNCTION

There are three main functions of vitamin A 

1. Maintenance of vision, particularly night vision. 

2. Maintaining of epithelial tissue and differentiation of many other tissues particularly during reproduction and gestation. 

3. Immunological role: Vitamin A plays an important role in regulating cell differentiation and thus maintaining epithelial barrier defense and modulating various components of the innate and acquired immunity, help maintain disease resistance and improve healing. Vitamin A deficiency (VAD), results in downregulation of T-cell mediated effectors function. Also VAD influence the Th 1Th2 (shift from Th2 to Th1) cytokine profile, resulting in greater secretion of proinflammatory cytokines. Vitamin A defi ciency is common among women in the developing countries. Mean serum concentration of vitamin A reserve is about 300 µg during pregnancy among diverse groups of South Asian women in comparison to value of 450–500 µg of better nourished Western population. Concern about maternal nutrition and VAD has been focused on its adverse effect on fetal and infant vitamin A status, health and survival. Randomized control trial of low dose of vitamin A or carotene revealed low mortality related to pregnancy in Nepal. Trials are on the way to show effi cacy of vitamin A supplementation on neonatal sepsis and necrotizing enterocolitis in developing countries, where vitamin A status of newborn is low, which predisposes to neonatal sepsis, an important cause of neonatal mortality.

Burden of Disease Attributing to Vitamin A De?ciency

Published study revealed diarrhea-associated death increased by 24% and measles-associated death increased by 20% due to vitamin A deficiency. Similarly as estimated by DALYs burden of VAD contributes significantly on global disease burden. Nutritional intervention with vitamin A supplementation is cost-effective. Randomized control trial have showed nutritional intervention with vitamin A supplementation, along with breastfeeding, complementary feeding and zinc supplementation can prevent 2.4 million child death per year globally which is 25% of total under fi ve death.

SOURCES OF VITAMIN A 

Carrots, dark green leafy vegetables, squash, orange and tomato are good source of vitamin A. Th e richest source of 

vitamin A include oil extracted from shark and cod liver. Also goat liver contains vitamin A.Many processed foods and infant formula are fortified with preformed vitamin A. Clinical conditions which predispose children to vitamin A deficiency 

• Undernutrition, particularly severe undernutrition 

• Fecal loss associated with recurrent and persistent diarrhea 

• In measles, VA falls short of increased demand by epithelial tissue 

• Zinc deficiency: RBP is zinc metalloenzymes, which carries retinol to retina, required for dark adaptation 

• Maternal vitamin A deficiency, which is frequently prevalent among women in developing countries 

• Polished rice as staple food with little or no vegetables or fruits.

CLINICAL FEATURES OF VITAMIN A DEFICIENCY 

Ocular

Vitamin A deficiency has public health importance as vitamin A plays an important role in vision, growth, reproduction, cellular differentiation, immunity and maintains epithelial integrity. VAD is one of the most common nutritional deficiencies in developing countries. VAD exerts effects through: 

• Direct action on retina and 

• Indirectly by increasing vulnerability to infections.

Xerophthalmia

Due to direct effect on retina, it is estimated that 5,000,000 preschool children become blind every year owing to vitamin A deficiency. Associated with malnutrition (blinding malnutrition) it increases the case fatality of SAM (severe acute malnutrition). Defective dark adaptation is the most important and frequent clinical presentation of vitamin A deficiency, resulting in night blindness. The syndrome of VAD consists of Bitot’s spot, xerophthalmia, keratomalacia, corneal opacity, hyperkeratosis, growth failure and death (Figs 35 to 38). Th e defi ciency disease in human was called Xerophthalmia (dry eye) because of prominence of the eye sign. WHO classifi cation of Xerophthalmia shown in Table 21. Other features include infertility, keratinization of epithelial tissue particularly in the skin (toad’s skin), urinary calculus and fetal abnormality.  Laboratory test shows level of serum retinol level of 15 µg/ dL or (normal 20–80 µg/dL)

TREATMENT OF VITAMIN A DEFICIENCY 

Specific treatment consists of oral administration vitamin A in a dose of 50,000 IU, 100,000 IU and 200,000 IU in children age less than 6 months, 6–12 months, more than 1 year, respectively. Th e same dose is repeated on next day and 2–4 weeks later. Parenteral Vitamin A Parenteral vitamin A (water soluble) can be administered in children with intractable vomiting and malabsorption. Th e dose is half of oral dose.  In addition, local treatment with antibiotic drop, ointment atropine and padding of eye should be done.

PREVENTION 

National Vitamin A Prophylaxis Program

 Vitamin A capsule 

 Vitamin A capsule of 200,000 IU is given to children irrespective of vitamin A status, starting from 6 months (100,000 IU up to 1 year) to 5th birthday .

 It should also be provided in predisposing clinical condition vulnerable to VAD, like severe malnutrition, measles, persistent diarrhea. 

 Dietary improvement is undoubtedly the most logical and sustainable strategy to prevent VAD. A change in dietary habit and increased access to vitamin A rich foods are required