Beta Carotene has the Most Vitamin A Activity of the Carotenoids
Carotenoids are oil-soluble plant pigments that the body can convert to vitamin A. They are responsible for the bright colors of produce. The best known carotenoid is beta-carotene. Beta carotene is a precursor to vitamin A. In other words, it is a building block; It provides raw material the can become vitamin A, but the body needs to convert it. Vitamin A is important for growth, reproduction, eyesight, membrane integrity and immune function.
Beta carotene contributes to the color in many fruits and vegetables. Actually, there are many carotenes, but beta carotene is the one that is most readily converted to vitamin A. Vitamin A (already converted) is found in animal products like meat and eggs.
Studies performed at the Agriculture Research Service (the chief research agency of the U.S. Department of Agriculture) and published in Agricultural Research, March 2001, show that beta-carotene absorption and conversion is not very good in some people. About half of 45 volunteers didn’t absorb much beta-carotene at all. About half of the volunteers didn’t form much vitamin A from the beta-carotene that they did absorb. This variation may be due to genetics.
One of the early symptoms seen in vitamin A deficiency is night blindness. Xerosis is another common symptom. In xerosis the eyeball loses its luster, becomes dry and inflamed and visual acuity is reduced. Other signs of deficiency include rough, dry or prematurely aged skin; loss of sense of smell; loss of appetite; frequent fatigue; skin blemishes, sties in the eye and diarrhea. Also the hair loses luster and sheen, dandruff accumulates and fingernails become brittle. In severe deficiency there may be corneal ulcers and softening of the bones and teeth.
Vitamin A is valuable in fighting infections. It protects the mucous membranes against invading bacteria. It is useful for people with allergies or who are exposed to pollutants. The itchy eyes experienced by hay fever sufferers is usually easily relieved by vitamin A.
Approximately 90 percent of the body’s vitamin A is stored in the liver, with small amounts deposited in the fat tissues, lungs, kidneys and retinas of the eyes. Zinc is needed to mobilize vitamin A out of storage. This is why so many of the symptoms of zinc deficiency are similar to the symptoms of vitamin A deficiency.
The RDA of Vitamin A, is between 1500-4000 IU for children and 4000-5000 IU for adults. Research indicates that no more than 50,000 IU per day can be utilized by the body. Higher doses can be given short-term. In third-world countries a single dose of 250,000 IU is often given to prevent blindness.