OVERVIEW oF VITAMIN A DEFICIENCY

  • Vitamin A: A family of lipid-soluble compounds (retinols, β-carotenes [provitamin A], and carotenoids) known as retinoic acids.
  • Key roles: Phototransduction (particularly night vision), epithelial tissue growth/differentiation, bone growth, and immune function.

DIETARY SOURCES & ABSORPTION

  • Food sources:
    • Retinol-rich foods: Liver, egg yolk, kidneys, fish oils, and butter.
    • β-Carotene sources: Green leafy vegetables (e.g., spinach), carrots, sweet potatoes, apricots, tomatoes, pimentos.
  • β-Carotene → Vitamin A: In the GI tract, 1 molecule β-carotene can yield 2 molecules of vitamin A.
  • Absorption:
    • Occurs in jejunum and ileum.
    • After absorption, enterocytes form retinyl-esters → packaged into chylomicrons → lymphatics → plasma.
    • Chylomicron remnants (with apo B and apo E) are taken up by the liver, and vitamin A is stored in hepatic stellate cells.
    • 50-85% of total body vitamin A is stored in the liver.
    • Upon release, vitamin A circulates bound to retinol-binding proteins (RBPs).

FUNCTIONS

  1. Vision:
    • Necessary for retinal photoreceptor function (especially rod cells for night vision).
    • Deficiency → decreased retinal 11-cis-retinol and rhodopsin, hence night blindness (nyctalopia).
  2. Epithelial Tissue:
    • Involved in growth/differentiation of epithelial cells.
    • Deficiency → dryness (xerosis) and keratinization of mucosal surfaces (e.g., eyes).
  3. Bone Growth:
    • Supports normal bone development.
  4. Immune Function:
    • Involved in maintaining immune competence.

CLINICAL MANIFESTATIONS OF DEFICIENCY

  • Night Blindness (nyctalopia): Earliest symptom of vitamin A deficiency.
  • Xerophthalmia: Progressive eye disorder with:
    • Xerosis (dryness of the conjunctiva)
    • Bitot spots (triangular grayish patches of keratinized epithelium on sclera)
    • Keratomalacia (corneal thinning) → can lead to perforation and blindness.
  • Other Symptoms:
    • Follicular hyperkeratosis on skin.
    • Impaired bone growth.

DIAGNOSIS

  • Often due to inadequate dietary intake or malabsorption.
  • Serum vitamin A (retinol) level <100 μg/L indicates severe deficiency (normal reference range: ~325–780 μg/L in adults).

TREATMENT

  • Severe deficiency (e.g., xerophthalmia):
    • High-dose therapy: ~60 mg of vitamin A immediately, then repeated 1 and 14 days later.
  • Milder deficiency (night blindness, Bitot spots):
    • Lower doses: ~3 mg daily for 3 months.
  • Also address underlying causes (poor diet or malabsorption).

PREVENTION

  • Recommended daily allowance:
    • Men: 900 μg retinol/day
    • Women: 700 μg retinol/day
    • Pregnancy/lactation: ~1.4 mg/day
  • 1 μg retinol = 12 μg β-carotene.
  • Met by balanced diet rich in milk, eggs, fish, butter, yellow/dark green vegetables.

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