Organic compounds that are essential for normal body growth and maintenance. They are classified into two groups: fat-soluble ( A, D, E, and K) vitamins, and water-soluble vitamins ( B and C). Vitamins are measured in very low concentrations, such as 1–100 mg. Through biochemical action, they perform various functions in such processes as cell growth, normal digestion, manufacture of red blood cells, and absorption of calcium and phosphorus. Inadequate vitamin intake can be the result of food deficiency, increased vitamin requirements, and increased vitamin loss. The vitamins of determined importance include: A (retinol), B1 (thiamine), B2 (riboflavin), B5 (pantothenic acid), B6 (pyridoxine), B12 (cyanocobalamin), C (ascorbic acid), D2 (calciferol), E (tocopherol), K, niacin, folic acid, and biotin.
