Vitamin A

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

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.