Vitamin A (retinol) fulfills multiple functions in vision, cell growth and differentiation, embryogenesis, the maintenance of epithelial barriers and immunity. A large number of enzymes, binding proteins and receptors facilitate its intestinal absorption, hepatic storage, secretion, and distribution to target cells. In addition to the preformed retinol of animal origin, some fruits and vegetables are rich in carotenoids with provitamin A precursors such as β-carotene: 6μg of β-carotene corresponds to 1μg retinol equivalent (RE). Carotenoids never cause hypervitaminosis A. Determination of liver retinol concentration, the most reliable marker of vitamin A status, cannot be used in practice. Despite its lack of sensitivity and specificity, the concentration of retinol in blood is used to assess vitamin A status. A blood vitamin A concentration below 0.70μmol/L (200μg/L) indicates insufficient intake. Levels above 1.05μmol/L (300μg/L) indicate an adequate vitamin A status. The recommended dietary intake increases from 250μg RE/day between 7 and 36 months of age to 750μg RE/day between 15 and 17 years of age, which is usually adequate in industrialized countries. However, intakes often exceed the recommended intake, or even the upper limit (600μg/day), in some non-breastfed infants. The new European regulation on infant and follow-on formulas (2015) will likely limit this excessive intake. In some developing countries, vitamin A deficiency is one of the main causes of blindness and remains a major public health problem. The impact of vitamin A deficiency on mortality was not confirmed by the most recent studies. Periodic supplementation with high doses of vitamin A is currently questioned and food diversification, fortification or low-dose regular supplementation seem preferable.
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