Organic substance present in minute quantities in natural foods that are essential for health, classified as either water soluble or fat soluble. Fat soluble vitamins include A (retinol), D (cholecalciferol), K (phytomenadione), and E (α-tocopherol). Water soluble vitamins include C (ascorbic acid), B1 (thiamine), B2 (riboflavin), B6 (pyridoxine), and B12 (cyanocobalamin), as well as nicotinic acid, folic acid, pantothenic acid, and biotin. Their absence from the diet or presence in insufficient amounts results in specific abnormalities, due to the derangement of particular metabolic processes: these include eye disease (A), rickets and osteomalacia (D), haemorrhagic problems (K), scurvy (C), beriberi (B1), and anaemia (B12).