What is Vitamin A?
Vitamin A is a fat soluble vitamin that is also a powerful antioxidant. Vitamin A plays a critical role in maintaining healthy vision, neurological function, healthy skin, and more. Vitamin A- like all antioxidants- is involved in reducing inflammation through fighting free radical damage. Consuming a diet high in antioxidants is a way to naturally slow aging.
Vitamin A deficiency is common throughout the world in
underdeveloped, overpopulated countries. It is estimated that worldwide, 80,
000 children a year become blind as a result of vitamin A deficiency and about
one-half of these children die.
Vitamin A is present in our food in two forms. In food of
animal origin it is found as the active vitamin (retinol), while in plant foods
it is found as provitamin-A carotenes, a precursor of vitamin A. Carotene is an
orange-yellow pigment that is present in green vegetables, but is masked by the
green color of the chlorophyll in the leaves. A precursor, or provitamin, is a
substance that is changed in the body to vitamin A. This takes place in the
wall of the small intestine. The amount that is changed varies between 30 and
70 percent, depending on the type of food and the form in which it is eaten.
Carotene itself is not active in the body.
In most of the food we eat about half of the vitamin A is in
the form of retinol and the other half is provitamin A. The liver stores about
90 to 95 percent of our vitamin A, enough to last months or perhaps even years
under normal circumstances.
Functions of Vitamin A
- Gives the ability to see in dim light.
- Maintain normal skin.
- Needed for growth and development of strong bones and teeth.
- Needed for the secretion of mucus by the cells lining the respiratory, urinary, and intestinal tracts that helps keep them moist and healthy.
- Aids the normal reproductive processes.
- Needed for carbohydrates metabolism in the liver.
- Essential for proper smell, hearing, and taste.
- Aids in the prevention of certain types of cancer.
- Beta carotene is a non-toxic antioxidant and helps prevent disease by neutralizing free radicals.
Deficiency of Vitamin A
- Poor vision in dim light (night blindness)
- Dry, scaly, itching skin.
- Increased susceptibility to infections, especially in the respiratory tract.
- Changes in the eyes that may lead to blindness. The eyes becomes dry, swollen, and infected. This condition is called xerophthalmia.
- Slow wound healing.
- Poor bone growth in children.
- Defective enamel on teeth and an increased number of cavities.
- Loss of taste and smell.
- Stunting of body growth. See Fighting vitamin A deficiency
Vitamin A Toxicity
Because vitamin A cannot be
excreted from the body in any significant amount, toxicity results from
prolonged daily doses in excess of 50, 000 IU in adults and less in children.
The symptoms of an overdose are nausea, diarrhea, headache, dizziness, loss of
hair, bone pain, dry itching skin, drowsiness, and cessation of menstruation.
These symptoms will clear up in a few days if the excess intake is stopped.
Toxicity only occurs with retinol and not with carotene. An excess intake of
carotene will cause the skin to turn yellow. This can be seen in those who
drink large amounts of fresh carrot juice.
Sources of Vitamin A
- Deep yellow vegetables such as carrots, pumpkin, sweet potatoes, winter squash, yellow corn, tomatoes.
- Dark green vegetables such as broccoli, chard, spinach, beet greens, collards.
- Yellow fruits such as apricots, cantaloupe, peaches, persimmons, oranges, mangoes.
- Watermelon. More see here Top 10 vitamin foods
VITAMIN A STABILITY
Very little vitamin A is lost
during cooking or processing. It is stable to heat and alkali, but not when it
is exposed to acids, light, or oxygen
