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Vitamin A

Alternate Names

  • retinol
  • retinal
  • retinoic acid
  • carotenoids including beta-carotene

Definition

Vitamin A is a fat-soluble vitamin, which means it can be dissolved in fat rather than in water. Vitamin A is carried through the body by fat. The body stores this type of vitamin in fat tissue rather than passing the excess out of the body. Thus, getting too much can be harmful.

What food source is the nutrient found in?

Vitamin A can come from animal sources such as:
  • eggs
  • fortified milk
  • liver
  • oils of some fish
This form of Vitamin A is called retinal or retinol. Vitamin A is also found in plants in another form, one called carotenoids. Beta-carotene is one of the most common carotenoids. These are converted into vitamin A in the body. Carotenoids are pigments found in deep orange, red, and yellow fruits and vegetables. They are also found in many dark-green leafy vegetables, such as:
  • carrots
  • pumpkin and other squashes
  • sweet potatoes
  • cantaloupe
  • broccoli
  • spinach

How does the nutrient affect the body?

Vitamin A helps develop and maintain healthy growth in the cells and almost all the parts of the body. It is especially key for proper night vision, but is also needed for the health of a person's:
  • teeth
  • skeletal and soft tissue
  • skin
  • mucous membranes
Vitamin A plays a key role in the immune system by helping protect from infections. Beta-carotene is an antioxidant. It has been studied for its role in cancer and heart disease protection. Antioxidants help fight free radicals, which are toxic oxygen by-products produced when body cells burn oxygen. A build up of free radicals can damage body cells and tissues.

Information

Vitamin A is usually measured in retinol activity equivalents, also called RAE. The Recommended Dietary Allowance, called RDA, for vitamin A for adult men, from age 11 on, is 900 RAE per day. Women, from age 11 on, should get 700 RE per day. Pregnancy adds only about 50-70 RAE in additional requirements, but lactating women need about 500-600 RE or more per day.
Vitamin A can be stored in the fat tissues of the body. This can pose a problem for people taking extra doses of vitamin A. High doses can be toxic and cause symptoms including:
  • headaches
  • dry and scaly skin
  • liver damage
  • bone and joint pain
  • vomiting or lack of appetite
  • abnormal bone growth
  • nerve damage
  • birth defects
In most cases, only levels 10 times the RDA (far more than a person could get through diet alone) have been linked with these symptoms. Vitamin A cannot reach toxic levels unless a person is taking extra doses. Carotenoids are not converted to vitamin A fast enough to increase the amount of vitamin A stored in the body; therefore, beta-carotene is NOT toxic to the body.
Getting too little vitamin A can cause disease also. Symptoms of significant deficiency include:
  • lowered resistance to infections
  • problems with getting pregnant
  • poor growth
  • improper tooth formation
  • rough, dry, and pimply skin
  • digestive problems
  • night blindness
  • eye disease, including xerophthalmia (zear-off-thal-me-ah), a condition in which the clear covering of the eye known as the cornea becomes dry and dull.
Vitamin A is an important fat-soluble vitamin. An individual needs to eat a variety of fruits, vegetables, lean meats, and fortified dairy products to ensure optimal intake of vitamin A. The information on food labels can help one choose foods with adequate vitamin A content.

Sources

Mahan, K, MS, RD, CDE&Escott-Stump, S., MA, RD, LDN. (2000). Krause's Food, Nutrition,&Diet Therapy (10th ed.). Pennsylvania: W.B. Saunders Company.

Somer, E., MA, RD.&Health Media of America. (1995). The Essential Guide To Vitamins and Minerals (2nd ed.). New York: HarperCollins Publishers, Inc.

Duyff, R., MS, RD, CFCS. (1996). The American Dietetic Association's Complete Food&Nutrition Guide. Minnesota: Chronimed Publishing.

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