Vitamin amino acids. Most vitamins are not single molecules, but groups of related molecules called vitamers. For example, vitamin E consists of four tocopherols and four tocotrienols. The thirteen vitamins required by human metabolism are: vitamin A (retinols and carotenoids), vitamin B (thiamine), vitamin B (riboflavin), vitamin B (niacin), vitamin B (pantothenic acid), vitamin B (pyridoxine), vitamin B (biotin), vitamin B (folic acid or folate), vitamin B (cobalamins), vitamin C (ascorbic acid), vitamin D (calciferols), vitamin E (tocopherols and tocotrienols), and vitamin K (quinones). Vitamins have diverse biochemical functions. Some forms of vitamin A function as regulators of cell and tissue
Vitamin K alter the tendency for blood-clot formation to occur. Unlike the safe natural forms of vitamin K and vitamin K and their various isomers, a synthetic form of vitamin K, vitamin K (menadione), is demonstrably toxic at high levels. The U.S. FDA has banned this form from over-the-counter sale in the United States because large doses have been shown to cause allergic reactions, hemolytic anemia, and cytotoxicity in liver cells. Phylloquinone (K) or menaquinone (K) are capable of reversing the anticoagulant activity of the anticoagulant warfarin (tradename Coumadin). Warfarin works by blocking recycling of vitamin K, so that the body and