Vitamin A

Functions

• promotes healthy eyes, skin, hair, teeth, and gums
• maintains integrity of epithelial membranes
• maintains resistance to infections
• necessary for formation of rhodopsin and prevention of night blindness
• cancer prevention

Deficiency

Mild

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

Severe

• loss of hearing, taste, and / or smell
• nerve damage
• Xerophthalmia, a characteristic eye disease
• 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
      • escarole, kale, spinach, turnip greens, and parsley
    • green, yellow, orange, or red
      • carrots, yams, squash
  • fruits
    • yellow and red
    • Pumpkin, cantaloupe, mango

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.
  • nausea and vomiting
  • constipation
  • headaches
  • insomnia
  • dry skin
  • joint pain
  • Excessive supplementation may also cause osteoporosis and increase risk of cancer
  • 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.
  • Others suggest 5000 to 10000 IUs
• Best taken with choline, essential fatty acids, vitamin C, vitamin D, vitamin E, and Zinc

Also see detailed report of Vitamin A.