Vitamin A plays an essential role in vision, particularly night vision, normal bone growth, reproduction, and the health of skin and mucous membranes. Vitamin A also acts in the body as an antioxidant, a protective chemical that may reduce the risk of certain cancers.
There are two sources of dietary vitamin A. Active forms, which are immediately available to the body, are obtained from animal products. These are known as retinoids and include retinal and retinol. Precursors, also known as provitamins, which must be converted to active forms by the body, are obtained from fruits and vegetables that contain yellow, orange, and dark green pigments or carotenoids. The best known is beta-carotene. Vitamin A is measured in micrograms (mcg): 1.0mcg RE is equivalent to 1.0mcg of retinol or 0.6mcg of beta-carotene.
Vitamin A is protected from being chemically changed by vitamin E. Vitamin A is fat-soluble and can be stored in the body. Most of the vitamin A you eat is stored in the liver. When required by a particular part of the body, the liver releases some vitamin A, which is carried by the blood and delivered to the target cells and tissues.
A common symptom of a severe deficiency of vitamin A is the eye disorder exophthalmia, in which the cornea hardens. This may progress to night blindness, corneal ulceration, and irreversible blindness. Other signs and symptoms include growth problems in children, poor wound healing, and dry, bumpy skin rashes known as follicular hyperkeratosis. Vitamin A deficiency can also affect the health of the epidermis (skin) and the normal functioning of mucous membranes throughout the body.
A good source of Vitamin A is found naturally in all these foods, which contain at least 0.15mcg of the vitamin per 50-200g:
- Sweet potatoes
- Butternut squash
- Liver (beef, pork, chicken or turkey)