Vitamin A deficiency and excess

Abstract

Vol. 24Vitamin A 129 dubious but in practice the results are very good-partly in fact because errors tend to be compensated ! Correction procedures devised specially to meet difficulties over vitamin A assays are actually theoretically safer in most of the many other situations in which they have been used ! I suppose there are lessons here as well as an element of irony.T h e problem of the site and manner of conversion of p-carotene into vitamin A was another problem which had its ups and downs, but the importance of processes occurring in the lining of the gut is beyond doubt. There have been interesting quantitative aspects of the storage of esterified vitamin A in the liver and its release as alcohol into the blood. The human requirement for vitamin A has been another problem with its own chequered history of good work done under difficulties, and the Sheffield wartime experiment on volunteers has its niche in the history of the subject.T h e deficiency syndrome was at first (perhaps necessarily) oversimplified, but as time has gone on appreciation of its complexities has grown. Hypervitaminosis A has in some respects been as revealing as hypovitaminosis, and experiments with tissue cultures have enriched notions based on experiments with intact animals. Links with the incidence of congenital abnormalities have shown that vitamin A can be teratogenic as well as indispensable. The variety of deficiency signs shown by different species has enlarged and complicated our outlook.My colleagues, Howell, Pitt and Thompson, have studied vitamin A acid (retinoic acid) with results which have not lost any interest to me through familiarity. I am left with a feeling that despite the enormous-and in many ways deeply satisfyingbody of knowledge about vitamin A we are still short of essential biochemical information. It is not my place in an introduction to speculate about the possibility of new light on the mode of action of vitamin A. I am here to listen. I am convinced, however, that the intellectual consummation of half a century of research has still to come. When it does we may be surprised at the sign-posts on the road which escaped our attention but were there all the time! REFERENCE McCollum, E.

Cell Type-specific Expression of β-Carotene 15,15′-Mono-oxygenase in Human Tissues

“…What is known, however, is that epithelia are sensitive to the vitamin A status. Deterioration of mucous membranes in the form of keratinization or atrophy is one of the characteristics of vitamin A deficiency (Wolbach and Howe 1925;Moore 1965). Many publications have described histological changes in the epithelia of different tissues during mild to severe vitamin A deficiency, e.g., atrophy of epithelium of rat esophagus (Mak et al 1987), mild atrophy, later accompanied by hyperkeratinization, of rat forestomach epithelium (Klein-Szanto et al 1982), a decrease in numbers of goblet cells in duodenal crypts in the rat (De Luca et al 1972;Rojanapo et al 1980), reduction of villous height and reduction of goblet cells and enterocytes in small intestine in rat , reduction of villous height and crypt depth in the small intestine of the chicken , hyperkeratinization of rat tongue epithelium with fewer and severely atrophied taste buds in the epithelium (Chole and Charpied 1983), keratinization of tracheal epithelium and atrophy of acini in submaxillary glands in rat (Anzano et al 1980), and keratinization of epithelium in rat urinary bladder (Hicks 1957).…”

Carotenoid and tocopherol levels in the serum of apparently healthy dairy cattle

“…The presence of adequate dietary levels of carotenoids and tocopherols is an important consideration in the nutrition of man and of domestic animals. Deficiencies or imbalances of the carotene derivative, vitamin A, can give rise to well-known disorders, such as defective dark adaptation and impaired growth rate (Moore, 1965), and lack of vitamin E has been associated with dystrophic muscular conditions in several species of animals (Hartley & Dodd, 1957;Blaxter & Brown, 1952). The interrelationships of these vitamins in biological systems have been investigated but apparently they are not well understood (Green, 1962).…”