Vitamins are essential nutrient molecules needed for enzymes to work in the body. Enzymes are often proteins that speed up chemical reactions for energy production or for building new tissues by forging new chemical bonds. Enzymes work with coenzymes and they cannot function without their essential vitamins. The fat-soluble vitamins are A, D, E and K; the body can store them in fat cells to use on demand. The water-soluble vitamins are the B-group and vitamin C. They are only stored in small amounts, they rapidly flush out, so deficiencies can more readily occur. All vitamins should be taken with food, because they are food derivatives: they are likely to be better absorbed along with other nutrients in meals, and will sit better in the stomach mixed with food.