Introductory Chapter: A Global Perspective on Vitamin A

Abstract

Vitamin A is a globally essential nutrient belonging to the group of fat-soluble vitamins that was first described in 1913 in a study of animals fed with ethereal egg or butter extract [1]. In the same year, Osborne and Mendel [2] made the first association of this vitamin with growth. Later, observations made by Steenbock [3] concluded their association with foods of yellow pigmentation (now known as β-carotene). The importance of vitamin A in vision health has been considered since ancient Egypt (1500 BC), where people suffering from night blindness were treated with a topical extract of hepatic liver extract (recognized today as a rich source of vitamin A) [3–6]. Its deficiency has typically been associated with continued malnutrition and childhood blindness; it is estimated that 254 million people suffer from vitamin A lack or related ocular disease [7]. It is now known that its benefits go beyond its role in vision yet include numerous essential metabolic and systemic functions [8]. To supply their metabolic functions and to avoid deficiency or overdosage, daily intake requirements were established according to their activity. This activity can be expressed as international units (IU) or retinol equivalents (RE): 1 IU is equivalent to 0.3 μg of total trans retinol or 0.6 μg of total all-trans-β-carotene, whereas 1 RE is equivalent to 1 μg of all-trans-retinol, 6 μg of all-trans-β-carotene, or 12 μg of another provitamin A carotenoids [9]. The recommended daily requirement for adult men and women is 900 and 700 μg RE/day, respectively, while 300 and 250 μg RE/day are the minimum intake limits. During pregnancy and lactation, recommendations are 700 and 950 μg RE/day, respectively [8, 9]. In the case of children in populations considered vitamin A deficient, doses of 60,000 μg RE/day are distributed twice a year [10]. According to Stephensen et al. [11], acute toxic reactions are uncommon at the dosages below 30,000 μg RE/day.