Some six years after the announcement of the discovery of vitamin A, attention was called1 to striking parallelism between the activity of vitamin A and the natural yellow color in plant sources of this food factor, Thus rutabagas, sweet potatoes and even yellow daffodils were shown to be superior in protecting experimental animals against the sequels of vitamin A deficiency than are the nonyellow varieties of the same plants. Later the yellowness was shown to be due to several hydrocarbon pigments that occur naturally in plants; alpha, beta and gamma carotene and cryptoxanthine are examples of this type of pigment which have come to be known as provitamins A. Obviously, carotene is transformed into vitamin A in the animal body, for when this pigment is fed, there results an accumulation of vitamin A. This circumstance, together with the fact that the liver is the most important site of storage
THE THYROID AND VITAMIN A. JAMA. 1948;137(1):91–92. doi:10.1001/jama.1948.02890350093013
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