Vitamins are commonly grouped according to solubility. A, D, E, and K are fat-soluble, and B complex and C are water-soluble (Table 7-3). In addi-tion, vitamin D is sometimes classified as a hormone, and the B-complex group may be classified as catalysts or coenzymes. When a vitamin has different chemical forms but serves the same purpose in the body, these forms are sometimes called vitamers. Vitamin E is an example. Sometimes a precursor, or provitamin, is found in foods. This is a substance from which the body can synthesize (manufacture) a specific vitamin. Carotenoids are examples of precursors of vitamin A and are referred to as provitamin A.