Vitamin A (retinol) is a yellow, fat-soluble solid terpene alcohol obtainedfrom some carotenoids by conversion in the liver, its storage organ.While carotenoids are widely distributed in such foods as green andyellow vegetables, retinol is not found in any vegetable sources, butis concentrated in egg yolks and the livers of many animals. VitaminA, either from animal sources or synthesized in our own liver, is essentialfor growth and reproduction, maintaining healthy vision, and supportingprotein synthesis and cell differentiation.* Vitamin A and its analogs have shown the ability to help maintain proper DNA function.* One study however, has shown that for certain lifestyles (e.g.,smokers) supplemental intake of too much beta-carotene in the absenceof other carotenoids and antioxidants (such as at least 400 IU/day ofvitamin E) may be harmful. Beta-carotene is the most potent precursor to vitamin A, but itsconversion to vitamin A in the body is limited by a feedback system. Itis an important antioxidant in its own right and one that can onlybuild up to toxic levels in rare circumstances. Beta-carotene helpssupport immune health by enhancing the function of the thymus gland.* Beta-carotene is an important antioxidant that also serves as an on-demand precursor to vitamin A.
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