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The medical importance of vitamin A and carotenoids (with particular reference to developing countries) and their determination.

Vitamin A, or retinol, is an essential nutrient for man and all mammalian species since it cannot be synthesised within the body. Deficiency of the vitamin results in adverse effects on growth, reproduction and resistance to infection. The most important manifestation of severe vitamin A deficiency (VAD) is xerophthalmia, and irreversible blindness may eventually occur in one or both eyes. VAD is still an important micronutrient deficiency problem in many developing countries, afflicting large numbers of pre-school children. It is often associated with protein-energy malnutrition, parasitic infestation and diarrhoeal disease. For many communities in developing countries, the major source of vitamin A in the diet is carotenoids. These compounds are synthesised only by photosynthetic microorganisms and by members of the plant kingdom where they serve important functions in metabolism, including participating in the photosynthetic process. These pigments also provide aesthetic qualities as colourants in the plant and animal kingdoms. Most importantly, the carotenoids serve the animal kingdom as sources of vitamin A activity. Major advances have occurred in understanding the role and mechanisms of action of carotenoids. They are now thought to play specific roles in mammalian tissues related to their function in plants. Carotenoids, with their highly reactive conjugated double bonds, act as free radical traps or antioxidants and may play an important role in the prevention of cancers. In view of the wide medical importance of carotenoids, much attention has been given to the determination of these pigments in foods as well as blood. Carotenoids in foods have conventionally been analysed using the open-column chromatography technique, but the high-pressure liquid chromatographic (HPLC) method is now gaining in importance as well. The classical method for the determination of carotenoids in blood is by the spectrophotometric method while the HPLC method is also recommended for use. An example of an HPLC method developed for the simultaneous determination of retinol and carotenoids in food and blood is given. The determination of retinol and carotenoids should be further developed in view of the wide importance of carotenoids in health and disease.