Beta-carotene
A pro vitamin, precursor chemical or building block that the human body converts to vitamin A, beta-carotene is one of many pigments called carotenoids that give the deep coloring found in orange or green vegetables and fruits.
Beta-carotene is the only carotenoid that can be converted to significant amounts of vitamin A, and only about one-sixth is converted in humans. Dietary fat is required for the adequate absorption of carotene. The deeper the orange coloring of a carrot, the higher the concentration of beta-carotene.
In an Arizona study, 26 of 49 patients with oral leukoplakia, a premalignant lesion, were given 60 milligrams daily of beta-carotene for six months, resulting in a significant reduction in the size of their lesions. However, excessive ingestion of beta-carotene and other carotenoids from dietary sources or supplements may cause a yellowing of the skin. Fortunately, the skin pigmentation
is reversible with reduction in the quantity of beta-carotene consumed. There is no evidence that natural sources of beta-carotene are more effective than synthetic sources.
Retinol
The major vitamin A compound is found naturally in eggs, dairy products, liver and fish-liver oil. The compounds require proteins for their absorption from the intestines. Etretinate, a synthetic retinoid, appears to be effective in the treatment of psoriasis. Half of 32 patients being treated for advanced cervical cancer had a 50 percent regression in the size of their tumors when treated with oral 13-cis-retinoic acid and alpha interferon.
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