Vitamin A

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Vitamin A: Bully at Croatian Wikipedia, Public domain, via Wikimedia Commons

Sources:-

  • Richest source: Fish Liver Oil(Cod Liver Oil)
  • Other good sources:-
    • Milk and dairy products
    • Dark green leaves such as spinach
    • Yellow and Red fruits and vegetables such as Carrots, tomatoes, and peaches

Biochemical Functions-

  • Role in Vision-
    • The cyclic events occurring in the process of vision- the Wald’s Visual Cycle requires rods and cones both of which contain  photoreceptor  pigments Rhodopsin and 11-cis-retinal respectively in their membranes and Vitamin A is a component of these pigments
    • There is increase in dark adaptation time in Vitamin A deficient individuals
  • Role in Color Vision-
    • Color vision is due to three different retinal pigments;-
      • Porphyropsin-Red
      • Iodopsin- Green
      • Cyanopsin- Blue
    • All these consist of 11-cis-retinal, of which Vitamin A is a vital component
  • Role in Cellular differentiation and metabolic effect:-
    • Retinoic acid is an important regulator of gene expression during spermatogenesis, embryonic development and differential epithelial cells
    • It controls biosynthesis of cholesterol and membrane glycoproteins and glycosaminoglycans.
  • Antioxidant function-
    • Beta carotene is an antioxidant playing a role in trapping peroxy free radicals in tissues.
    • Associated with anticancer activity
    • Elevated levels of dietary carotenoids have been associated with decreased risk of cardiovascular disease.

RDA-

Adults: 800-1000 retinol equivalents

Deficiency Manifestations

  • Effect on Vision:-
    • Nyctalopia- Night Blindness due to increased dark adaptation time.
    • Xerophthalmia- Dryness of cornea and conjunctiva, common in children.
    • Keratomalacia-
      • Prolonged xerophthalmia leads to keratinization, ulceration and destruction of cornea.
      • There is permanent loss of vision.
      • Common in children.
    • Bitot’s Spots- White opaque spots developed on either side of cornea in Vitamin A deficiency.
  • Effect on Skin-
    • Keratinization of epithelial cells of skin leading to-
    • Keratosis of hair follicles
    • Dry, rough, scaly skin
    • Keratinization of respiratory and urinary epithelium making them prone to infections
  • Other Effects:-
    • Failure of growth in children
    • Faulty bone modelling producing thick cancellous (spongy) bones
    • Degeneration of testes
    • Abortion
    • Birth defects.