Vitamins are a group of organic compounds that are indispensable to body function. Vitamins are divided into two broad categories according to their solubility characteristics. Vitamins A, D, E and K are insoluble in water but soluble in lipid or lipid solvents and they are thus classified as the fat-soluble vitamins. The water-soluble vitamins leach into cooking water and this can result in very substantial losses during food preparation. Stores of these vitamins tend to be smaller than for the fat-soluble vitamins and excesses tend to be excreted in the urine. Dietary deficiencies of vitamins give rise to clinically recognisable deficiency diseases that are cured by administering the missing vitamin. People meeting their energy needs and eating a variety of different types of foods seldom show clinical signs of vitamin deficiency. The epithelial changes seen in vitamin A deficiency resemble some of those seen in the early stages of epithelial carcinogenesis.