Final answer:
The best source of preformed vitamin A among the options given is fried liver. Liver contains retinol, the active form of vitamin A, in a high concentration, making it a direct and potent source of this fat-soluble vitamin.
Step-by-step explanation:
Of the following, the best source of preformed vitamin A is fried liver. Preformed vitamin A, also known as retinol, is readily used by the body and is found in its active form in animal-derived foods. The liver is an especially rich source of preformed vitamin A. While foods such as sautéed spinach, fresh mango, and cheddar cheese do contain vitamin A, it is primarily in the form of provitamin A carotenoids, like ß-carotene, which the body must convert to the active form.
Liver offers a direct source of preformed vitamin A, whereas the body synthesizes vitamin A from ß-carotene in foods like carrots and sweet potatoes. Vitamins are either fat-soluble or water-soluble, and vitamin A is fat-soluble, meaning it is absorbed through the intestinal tract with lipids in chylomicrons. The dietary sources of vitamin A to humans are through the conversion of beta-carotenes (plant sources) to vitamin A or the hydrolysis of retinyl esters (animal sources) to retinol in the intestine.
The body stores a significant amount of vitamin A in the liver as palmitate esters, indicating why animal liver is such a potent source of this nutrient. Cheddar cheese may also provide some vitamin A, but it would not be as significant as liver. Spinach and mango offer carotenoids, which are precursors to vitamin A and need to be converted in the body.