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Vitamin A deficiency can lead to blindness.

sources of vitamin A
Carotenoides are pigments that occur naturally in chromoplasts of plants, Fungi, and some bacteria. Carotenoids (chromoplasts pigment) absorbs light for the photosynthesis and protects the chlorophyll from photo damage.
During the ripening of almost all fruits, there occurs a disruption in the organization of chloroplasts Contains (Chlorophyll) and re-organization into Chromoplasts (Carotenoids). As the photosynthesis apparatus is dismantled and the chlorophyll is degraded, the color of existing Carotenoids is unmasked.This causes Green banana to appear yellow after unmasking of carotenoids. Flamingos are rich in Carotenoids diet thus their feather looks orange colored.
There are over 600 carotenoids known till today. Carotenoids are divided into two catogories:
1.Carotenes
2.Xanthophylls

Carotenes are pure hydro carbons.They are called anti oxidants and they include:
  • Alpha-Carotene
  • Beta-Carotene
  • Lycopene
  • Gamma-Carotene
Xanthophylls contain oxygen in their molecules.They can oxidize free radical in plants as well as animals.Thus they are called Anti-Oxidants and they include:
  • Lutin
  • Violaxanthin
  • Neoxanthin
  • Zeaxanthin
  • Mesoxanthin(Retina makes it with ingested lutin)
  • Beta Cryptoxanthin
Carotenoids absorb wavelengths ranging from 400-500 nanometers (Violet to Green). This cause the Carotenoids to appear yellow, red, orange.

Foods like Carrot, Apricot, Orange, Mango and Pumpkin contains Carotenes like beta Carotene, alpha carotene and other Carotenoids like Lutin, Zeaxanthin, beta Crptoxanthin. Carotenoids are responsible for the orange, red, yellow color of these foods. Other foods like Egg yolk, Corn, Bananas, Kale, Spinach etc. are also rich in Carotenoides.
Note:The color of spinach and kale are green as the Chlorophyll overrules the color of Carotenoids. Carotenoids are also the reason for the milk fat and butter to appear yellow.
Foods containing vitamin A

Our body converts the Carotenoides into Vitamin A. Not all Carotenoides are convertible but beta, alpha Carotene & beta Crptoxanthin are converted into Vitamin A in our body. These 3 are also called Pro-vitamin A because they can be converted to vitamin A in our body. The direct source of vitamin A is found from animal food. The vitamin A so directly obtained from animals need no conversion in the body. The vitamin A obtained from animal food is called Retinol i.e. another form of vitamin A. Vitamin A is stored in the liver in the form of Retinyl esters. Retinyl esters are easily converted to retinol when in need and vice versa. Retinyl palmitate, or vitamin A palmitate, is the ester of retinol (vitamin A) and palmitic acid. Retinyl palmitate is used as an antioxidant and a source of vitamin A added to low fat milk and other dairy products to replace the vitamin content lost through the removal of milk fat.

Types of Vitamin A:
  • Retinol: This alcohol form of vitamin A. The original state of vitamin A found in the body and can be obtained by animal foods directly. Most abundant from of Vitamin A in our body. Can be converted to Retinal ester for storage in the liver.
 Retinol + NAD+  retinal + NADH + H+
  • Retinal: This is aldehyde form of vitamin A also called as retinaldehye. Retinal is produced by oxidation of retinol or betacarotene as retinol and retinal are interchangeable. Retinal reacts with opsin protein in the retinal rod cells to form rhodopsin pigment for layer of rods and cones.
beta-carotene + O2 → 2 retinal
retinal + NADPH + H+  retinol + NADP+
  • Retinoic acid: Also called as vitamin A acid, used by skin for making epithelial cells. Also used in acne treatment as “isotretinoin”
     retinal + O2 + H2O → retinoic acid + H2O2
So, the vitamers of vitamin A  i.e. those compounds that are eligible to be said vitamin A are "Retinol, Retinal, Retinoic acid, beta carotene, alpha carotene, and beta cryptoxanthin". The retinoids are pharmaceutical forms of vitamin A.

Deficiency of vitamin A:
The condition in eye is called as xerophthalmia. The dryness state of the eye. The Retinoic acid is responsible for mucous secreting epithelial cells. Vitamin A itself produce "Mucopolysaccharide" in goblet cells. The lack of mucin and inadequate tear film from main lacrimal gland cause the cornea and conjunctiva to dry out also called as "Keratomalacia". The retina is affected as the retinal (retinol) that forms Rhodopsin are absent which leads to the "Nightblindness". Night blindness so caused can be cured but corneal keratinization is hard to cure.
Stages:

  • Night blindness: Inability to form Rhodopsin for rod cells(Opsin protein of rods+retinal).
  • Bitot spot: Build up of keratin on the conjunctiva as a early sign.
bitots spot in vitamin A deficiency
  • Conjunctival xerosis: Lack of mucin and lacrimal tears cause dryness of conjunctiva.
  • Corneal xerosis: Lack of retinoic acid to maintain corneal epithelium.
  • Corneal ulcer: Infection to corneal epithelium which is eroded by xerosis.
  • Corneal opacity: Opacity is formed after the stromal defects heal.
  • Xerophthlmic fundus: Lack of retinoic acid cause xerosis of epithelium of retina and no production of rhodopsin and scarcity of retinal (retinol) in  the retina.
Treatment and Cure:

feeding vitamin A to a kid

  • Artificial tear drops for the xerosis of cornea and conjunctiva.
  • Treatment of corneal ulcer.
  • Vitamin A dose to re supply the body with retinol, so that rhodopsin is re formed and retinal (retinol) is reformed epithelial damage stops. The lacrimal gland and glands of conjunctiva starts working again.
  • Women of reproductive age (Pregnant or not) is treated with daily dose of 10,000 I.U vitamin A for 2 weeks.
  • Patients above age of 1 is treated with 200,00 I.U orally or 100,000 I.U intramuscular injection in case of diarrhoea. (Not women of reproductive age)
  • Child under the age of 1 or if weighs less then 17pounds (8Kilograms) is treated with the half dose of those over 1 years of Old.
World Prevalence of vitamin A caused Blindness:
blind kid due to keratomalacia

According to WHO report An estimated 250 million preschool children are vitamin A deficient and In vitamin A deficient areas, a substantial proportion of pregnant women is vitamin A deficient. An estimated "250 000" to "500 000" vitamin A deficient children become blind every year, and half of them die within 12 months of losing their sight”
Each year in Nepal, vitamin A deficiency is responsible for the deaths of 9000 children and for 2500 children becoming permanently blind.

About the author:  Niranjan Gaire is the Incharge at Rukum Eye Care Centre, Nepal Netra Jyoti sangh