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Vitamin A Test Importance, Functions, Food Sources, Deficiency, Disorders Treatment

Vitamin A Test Importance, Functions, Food Sources, Deficiency, Disorders Treatment

Posted By HealthcareOnTime Team Posted on 2022-01-13

Vitamins are micronutrients which play a crucial role in maintaining various biological processes in human body. These are classified broadly into two groups, viz. water-soluble and fat-soluble. Vitamin A is an important member of fat-soluble vitamins group which plays a vital role in maintaining good vision and aids cellular growth.

Vitamin A Test Importance, Functions, Food Sources, Deficiency, Disorders Treatment

Discovered in the year 1913, it was initially termed as the "anti-infective vitamin", mainly because it was found to confer resistance against various infectious diseases. Even before the discovery of this fatsoluble vitamin, cod liver oil was being used for the treatment of xerophthalmia and rickets. It was in 1922 that McCollum and his team identified the presence of two fat-soluble vitamins (A&D) in cod liver oil which were effective for treatment of these conditions. Further study of this vitamin aided chemists to classify it as a fat-soluble organic compound which exists in two main forms, viz. preformed vitamin- retinol and provitamin carotenoids. Provitamin carotenoids include acarotene, B-carotene and y-carotene. Retinol is mainly obtained from animal and dairy products, while B-carotene is obtained from plant sources.

A recent report has stated that worldwide approximately 4.4 million preschool kids develop visible vision damage due to Vitamin A deficiency, and close to 20 million pregnant females in developing countries suffer from this deficiency. Out of these affected population, nearly one-half of the cases occur in India.

Mechanism of absorption in the body
Since vitamin A is fat-soluble in nature, it cannot be directly absorbed from the diet, and hence it is first solubilised to micelles in the intestinal lumen and further absorbed by the duodenal mucosal cells.

The provitamin A obtained from plant source, is absorbed through the linings of the small intestine which converts it to retinol and can be stored in the liver as retinyl esters.

Retinol is transported in the bloodstream by the Retinol Binding Protein (RBP), which is synthesised in the liver.

Thus, carotenoids undergo a series of enzymatic conversion from retinol, further oxidised to retinal and finally retinoic acid.

Prevalence of deficiency
Vitamin A deficiency is the leading cause of preventable blindness in children. It also increases risk of various diseases and in some cases death from severe infections. In many pregnant women, deficiency has also been associated with increased risk of maternal mortality. Globally, preschool aged children and women of reproductive age are the worst affected groups and are at the highest risk of developing nutritional deficiency related disorders. A recent report has stated that worldwide approximately 4.4 million preschool kids develop visible vision damage due to vitamin A deficiency, and close to 20 million pregnant females in developing countries suffer from this deficiency. Out of these affected population, nearly one-half of the cases occur in India.

The major sources for this powerful vitamin include vegetables like sweet potato, spinach, carrots, tomato, etc. Animal sources include hard boiled egg, chicken breast, salmon, tuna, etc. Apart from these, yogurt, pistachios, mangoes and dried apricots are also packed with vitamin A. Fortified ready-to-eat cereals are also available these days, and in case of detected deficiency, supplements of vitamin A are also available to be prescribed by the physician. It usually contains vitamin A in the form of retinyl palmitate or retinyl acetate."

- Promotes growth of strong teeth and bones.
- Plays an important role in normal brain develop ment and functioning of the nervous system.
- Maintenance of a healthy skin texture and prevents dry skin.
It is essential for maintaining a good eye-sight and promoting vision especially in low light as it is involved in synthesis of certain pigments in the retina.
- Carotene acts as an antioxidant and protects cell damage by free radicals, and plays a crucial role in preventing cancer development.

Deficiency disorders
Vitamin A deficiency, clinically can cause several complications, majorly Xeropthalmia.

This condition encompasses all the defects which affect the eyes. It can occur secondary to many clinical autoimmune disorders like Sjogren's syndrome, rheumatoid arthritis, systemic lupus erythematosus, as side affects of certain medicines and also due to deficiency of vitamin A. It results due to inadequate functioning of the lacrimal glands, which is responsible for forming a tear film over the cornea. Thus, this condition is also termed as "dry eyes". If xerophthalmia is due to vitamin A deficiency, the condition begins with night blindness and conjunctival xerosis (dryness of the eye membranes), progresses to bitot's spot and corneal xerosis (dryness of the cornea), and in its later stages develops into keratomalacia (softening of the cornea).

1. Night blindness (XN) As the name implies, XN indicates complete lack of vision at night, or inability to see at night or in low light and is the first symptom of vitamin A deficiency Human retina has specialised photo receptor cells called rods (for light vision) and cones (for colour vision), of which rods are imperative for good vision especially in low light or night. XN arises due to reduced synthesis of the pigment rhodopsin present in the rods due to vitamin A deficiency. Though XN can be both hereditary and acquired, most of the cases in developing countries are acquired due to malnutrition.

2. Conjunctival xerosis (X1A) It is a condition accompanied by extreme dryness of the eye surfaces caused by deficiency of tears or conjunctival secretions. It is mainly caused due to loss of goblet cells of the conjunctival epithelium. This condition precedes the more severe stage of corneal xerosis.

3. Bitot's spot (X1B) It involves build-up of keratinised material on the surface of conjunctiva, and can be oval, triangular or irregular in shape and is usually presented on the temporal (outer) side of the conjunctiva which is not covered by the eyelids. Extreme case of conjunctival xerosis leads to Bitot's spot. Histopathologically it is characterised by presence of a thickened superficial layer of flattened cells having a frayed keratinised surface with prominent gram-positive bacteria or in some cases even fungi.

4. Corneal xerosis (X2) This is a more advanced stage of lesions which represent severe vitamin A deficiency. However, it is highly reversible and can be treated using external vitamin A supplements

5. Keratomalacia (X3A, X3B) This is the last stage of xerophthalmia where there is complete destruction of cornea. It progresses rapidly and arises due to sudden and severe vitamin A deficiency. It usually affects both eyes and the severity can vary from mild to severe. In extreme cases, it can also cause blindness and this stage is seen to affect younger children at a higher rate

6. Corneal scars (XS) Corneal scars occur due to injury, infection or xerophthalmia. Survivors of keratomalacia develop scars of various sizes on one or both sides of cornea. These can be of two forms viz. active and inactive. Inactive form of corneal scars are very commonly seen in young children as a sequelae to keratomalacia

Apart from Xeropthalmia, other conditions like cancer, measles and age-related macular degeneration (AMD) also occur due to vitamin A deficiency. AMD has been highlighted to be one of the major causes of vision loss in the older age group. Lower levels of vitamin A has also been shown to increase the severity and complications associated with measles.

Diagnosis of "Vitamin A" deficiency disorders
Assessing physical signs and clinical symptoms is essential to determine any nutritional deficiency disorder. Once the signs and symptoms have been assessed by the physician, following tests may be recommended for accurate diagnosis of deficiency. These are:

1. Lissamine green staining It involves staining of the conjunctiva, and is a new and widely heralded aid for diagnosing early xerophthalmia. Extent of damage or staging of the condition is done by observing the stained cornea.

2. Estimating vitamin A levels - Serum estimation of vitamin A levels is also considered to be an efficient diagnostic tool to detect deficiency. Technologies like LC-MS/MS (Liquid Chromatography-Mass Spectrometry) have been widely recognised for their sensitivity and specificity for diagnosis of micro-vitamin deficiency disorders as well as toxicity.

Treatment of disorders Treatment of any nutritional deficiency involves diet pattern modification to include foods rich in the deficient nutrient. In case of vitamin A deficiency, inclusion of coloured vegetables rich in carotene along with supplementation is recommended. Limiting uptake of solid fats, cholesterol and salt while maintaining a healthy calorie intake is also a must.

Vitamin A toxicity Hypervitaminosis can be majorly caused either due to excessive dietary intake of vitamin A or over consumption of supplements. Since, these are fat-soluble, they tend to accumulate in the liver and are not easily excreted by the body. Though, excess retention of B-carotene and other provitamin A is not deleterious, high levels of vitamin A can cause symptoms like nausea, headache, dizziness, skin irritation, joint pain, coma and even death.


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