Vitamin A

Vitamin A is an essential part of the biochemical machinery of all vertebrates. It is a derivative of carotenoid pigments from plants. As far as is known, no vertebrate can synthesize carotenoids de novo.¹Probably all higher animals can convert certain carotenoids to vitamin A. The pathologic consequences of the deficiency are similar in man, monkeys, cattle, swine, dogs, rabbits, guinea pigs, rats, mice and fowls.²For these and other reasons, facts about vitamin A learned from animal experiments are without doubt applicable to man. The required brevity of this article will not permit mention of many papers and excludes critical discussions. The selection and evaluation of the material presented are expressions of our judgment. Readers wishing more references are referred to a monograph by Browning,³to a review by Robertson⁴and to the recent volumes of theAnnual Review of Biochemistry.⁵ PHYSIOLOGY Vitamin A