Food sources of vitamin A
The richest natural sources of vitamin A are the fish-liver oils, which are usually classed as food supplements iller than as foods. They vary according to the species and the season when caught, but commercial brands are well standardized for our convenience.
All animal livers are good sources of vitamin A, but they are not as rich as fish liver. All milk products that include milk fat, such as whole milk, butter, cream, or full cream cheese, are rich in vitamin A. The milk of cows on green pasture is usually higher in vitamin A than is the milk of stall-fed animals.
Because margarines, lowfat and dried skim milk products and many ready- to-ea t breakfast cereals are now fortified with vitamin A, they contribute a significant amount to the total vitamin A intake.
Carotene is abundant in carrots, from which it derives its name, but it is also present in even higher concentration in certain green, leatyvegetables and grasses in which the color of the chlorophyll masks the yellow of the carotene. In certain species, such as corn, there is more carotene-hence, more vitamin-A activity-in yellow varieties than in white. There are African countries where red palm oil is used extensively and contributes greatly to the carotene intake.
Animal foods that contain mostly preformed vitamin A seem to be more efficient sources of this factor for humans than are the precursors found in plants. However, the ample supply of carotenes in plant foods may well contribute a large share of the vitamin A requirement. Cooking, pureeing, or mashing of vegetables ruptures the cell membranes and makes the carotene more available.
