Vitamin A

Retinol, Provitamin, Carotene

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Functions

  • maintains integrity of epithelial membranes
  • maintains resistance to infections
  • necessary for formation of rhodopsin and prevention of night blindness

Deficiency

Mild

  • retarded growth
  • increased susceptibility to infection
  • abnormal function of gastrointestinal, genitourinary, and respiratory tracts due to altered epithelial membranes
  • dry, shriveled, thickened skin, sometimes pustule formation
  • night blindness

Severe

Xerophthalmia, a characteristic eye disease, and other local infections

Characteristics

  • fat-soluble
  • not destroyed by ordinary cooking temperatures
  • destroyed by high temperatures when oxygen is present
  • marked capacity for storage in liver
  • carotene is a precursor to vitamin A

Good Sources

Natural

  • Retinol
    • milk fats
      • butter, cheese, cream, whole milk
    • egg yolks
    • liver
    • fatty fish
  • Carotene
    • vegetables
      • green leafy
        • especially escarole, kale, and parsley
      • green, yellow, orange, or red
        • especially carrots
    • fruits
      • yellow and red

Food Quantity mcg RAE
Egg 1 medium 118
Milk (non-fat) 1 cup 149
Nectarine 1 medium 50
Watermelon 1 piece 27

Artificial

  • irradiated fish oils, including fish liver oil

Recommended Daily Allowances (RDA)

  • Males (11 yrs. and older)
    • 900 mcg RAE
    • 1,000 mcg retinol equivalents
  • Females (11 yrs. and older)
    • 700 mcg RAE
    • 800 mcg retinol equivalents
  • Pregnant females
    • 1,000 mcg retinol equivalents
  • Lactating females
    • 1,200 mcg retinol equivalents
  • Children
    • 400-700 mcg retinol equivalents
  • Infants
    • 400 mcg retinol equivalents
  • Varied values reflect different references

Tolerable Upper Intake Levels (UL)

  • Adults (19 to 50 yrs)
    • 3000 mcg RAE

Intakes above UL may lead to negative health consequences. Excessive intake of carotene, from which vitamin A is formed, may produce yellow discoloration of the skin (carotenemia).

Supplementation

  • Not recommended, since toxic in high doses.
  • Excessive supplementation may also cause osteoporosis and increase risk of cancer.

Also see detailed report of Vitamin A.


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