Health Center Home

Vitamin A

Found in:
Sweet potatoes, carrots, apricots, pumpkin, romaine lettuce, spinach, parsley, squash, cantaloupe, beet greens, chard, collard greens, kale, mustard, turnip, butter, eggs, cheese, milk, chives, cabbage, tomato, papaya, oranges, beef, lamb, chicken, halibut, and sardines.

What is known to be good for:
Essential for healthy skin, eyesight and fighting infections. Vitamin A helps regulate the immune system, which helps prevent and combats infections by producing white blood cells that destroy harmful bacteria and viruses and helping lymphocytes (a type of white blood cell that help us fight infections) function more vigorously. Vitamin A also plays a significant role in vision, bone growth, reproduction, cell division and cell differentiation. It helps to maintain the membranous linings of the eyes and the respiratory, urinary, and intestinal tracts. Those linings protect the organs from being invaded by bacteria and viruses.

Other functions of Vitamin A:
The belief that vitamin A reduces cancer risk is based on the following observations:

  • The requirement of vitamin A for the maintenance of epithelial tissues, a common location where many cancers are located,
  • Tumor surveillance by the immune system is dependent on adequate levels of vitamin A, and
  • Gene expression may be directly influenced by vitamin A and retinoids.

Lack of Vitamin A can:
Vitamin A deficiency is one of the most prevalent forms of malnutrition in the world. Pregnant women, infants and young children are most susceptible. Vitamin A deficiency is associated with increased childhood morbidity and mortality. This is due to an increased risk of infectious diseases particularly in developing countries. The first symptoms of vitamin A deficiency are night blindness and drying of the conjunctiva of the eye. Bitot's spots may be present in the cornea of the eye. With continued vitamin A deficiency, progressive damage to the eye results from drying of the cornea and irreversible corneal damage resulting in xerophthalmia, keratomalacia, and blindness. In children, retarded growth may occur as a result of vitamin A deficiency.

Excess of Vitamin A:
Excessive ingestion of carotenoids, while not toxic to man, results in carotenemia and yellow discoloration of the skin. Chronic toxicity of vitamin A produces variable symptoms. These may include: anorexia, nausea, vomiting, abdominal pain, dry skin, rashes, headaches, loss of hair, abnormal skin pigmentation, increased fragility and pain in the long bones, menstrual irregularities and enlargement of the liver and spleen.

Do you know where you find Vitamin A in your body?
Membranous linings of the eyes and the respiratory, urinary, and intestinal tracts.

Storage and manipulation of suppliers of Vitamin A:
Vitamin A can be lost from foods during preparation, cooking, or storage. To prevent loss of vitamin A:

  • Use raw fruits and vegetables whenever possible.
  • Keep vegetables (except sweet potatoes and winter squash) and fruits covered and refrigerated during storage.
  • Steam vegetables and braise, bake, or broil meats instead of frying. Some of the vitamin A is lost in the fat during frying.

Absorption, Storage and Excretions
Absorption of vitamin A and the carotenoids requires the presence of bile in the intestinal tract and other conditions favorable for fat absorption. Conversion of the ingested carotene to vitamin A takes place primarily in the cells in the intestinal mucosa but also occurs in the liver and possibly the kidney. Retinoic acid, however, is absorbed directly into the intestinal mucosa and released into the portal circulation complexed with albumin. Storage of vitamin A occurs primarily in the liver as retinyl ester. When needed, retinol is mobilized from the liver and transported in the circulation to tissues complexed with retinol binding protein (RBP).

Source: HEINZ HANDBOOK of Nutrition, 9th. EDITION, Edited by David L. Yeung, Ph.D. and Idamarie Laquatra, Ph.D., R.D.

Adapted by Editorial Staff, January 2007
Last update, August 2008

 


Fit Portions 2004 - 2014  powered by Nutrihand, Inc.© Copyright 2004-2012 |  Technical Support