The World Health Organisation (WHO) estimates that 40 million children in the world suffer from vitamin A deficiency, but the incidence varies greatly from region to region. Approximately 350 000 infants and young children become blind annually because of vitamin A deficiency, and 70% of these die within one year.5 In a number of supplementation studies carried out in affected areas, it was found that there was on average a 33% reduction in mortality after supplementation, even though some studies reported no effect.6 Vitamin A (Retinol) is one of the fat-soluble vitamins, and it has a variety of functions. Vitamin A is one of the recognized anti-cancer vitamins in view of its antioxidant properties, but it also affords protection against infectious diseases, is essential for the formation of eye pigment, plays a critical role in growth and bone remodelling, maintenance of a healthy skin and epithelia, such as those of the respiratory tract and gastrointestinal tract, and it also plays a role in spermatogenesis and embryonic development.7 The need for vitamin A is increased in adolescents, and pregnant women require some 25% more vitamin A than non-pregnant women.8,9
Preformed vitamin A is found only in animal sources as it is usually associated with lipids, but provitamin A (β-carotene), the original source of retinol, is found in plant pigments. Vitamin A concentrations in the literature are normally given in International Units (IU). One IU is the equivalent to the biological activity of 0.3 mg of retinol or 0.6 mg of β-carotene. In 1974 the food and Nutrition Board of the US National Research council decided to replace the IU with the Retinol Equivalent (RE), as this measure accounts for the absorption and conversion of carotene to retinol. The equivalents of this unit are:
1 RE = 1mg retinol (3.33 IU)
1 RE = 6mg beta carotene (10 IU)
1 RE = 12mg other carotenoids (10 IU)
It thus takes six times more -carotene than retinol to meet the bodies needs, but on a vegan diet with plenty of fruits and vegetables, there is virtually no possibility of suffering from a vitamin A deficiency. In fact, oversupply can be a real danger especially in cases where large doses are taken as supplements. In its final state (as retinol) vitamin is toxic, and taking more than the recommended amount will lead to hypervitaminosis A the symptoms of which are fatigue, nervousness, headaches, dizziness and decalcification of bones. Vitamin A is poorly supplied in most meat dishes with the exception of liver, some fish and dairy products. RDA of vitamin A for adults is 1 000 RE/day for men and 800 RE/day for women. Vitamin A is moderately unstable and it is destroyed by heat, light, exposure to oxygen and acids. Diets rich in cooked animal products are thus not the best source of vitamin A. Provitamin A is, however, well retained in cooked vegetables, and a varied diet which includes pigmented fruits (particularly red and yellow) and green and yellow vegetables will supply ample vitamin A. Deficiency diseases in poor countries can be ascribed to a lack of fruits and vegetables in the diet and the fact that the diets of the underprivileged consist largely of grains which on the whole are poor suppliers of vitamin A.