Final answer:
Preformed vitamins are active forms of vitamins found in foods, such as vitamin A. They can be directly utilized by the body without conversion from precursors. Preformed vitamins can either be fat-soluble, which can be stored in the body, or water-soluble, which are not stored and excess amounts are excreted.
Step-by-step explanation:
Preformed vitamins are active forms of vitamins that are already in a form that the body can use immediately and are found in foods. An example of a preformed vitamin is vitamin A, which can be directly absorbed and does not need to be converted from a precursor. Vitamins are classified into two categories: fat-soluble and water-soluble. Fat-soluble vitamins, such as vitamins A, D, E, and K, are absorbed through the intestinal tract with fats and can be stored in the body's lipid stores. Vitamin D can also be synthesized in the skin from sunlight exposure. If an excess of fat-soluble vitamins is consumed, they can accumulate in the body and potentially lead to hypervitaminosis. In contrast, water-soluble vitamins, which include the B-complex vitamins and vitamin C, cannot be stored in the body and excess amounts are usually excreted in the urine.