Pro-vitamin A carotenoids

Wurtzel, E.T. et al.. Research towards improvement of the pro-vitamin A (carotenoid) content of rice endosperm, Int. Rice Res. Notes 21, 43, 1996. 

Scott KJ and Rodriguez-Amaya D. 2000. Pro-vitamin A carotenoids conversion factors retinol equivalents-fact or fiction Food Chem 69 125-127. 

In food, vitamin A exits in two forms preformed vitamin A (retinol and retinyl esters) in animal products and pro-vitamin A carotenoids... 

Due to their inability to synthesize retinol de novo, animals need to obtain retinoids through the diet, mainly in the form of carotenoids, such as P,P-carotene (Figure 1.1). Carotenoids are isoprenoids that are widespread in nature and are typically associated with the yellow, orange, red, or purple colors found in vegetables, fruits, flowers, birds, and crustaceans (Fraser and Bramley 2004). Alternatively, retinol can also be taken up directly in the form of pro-vitamin A carotenoids (Blomhoff and Blomhoff 2006). 

Two groups of compounds, shown in Figure 11.2, have vitamin A activity retinol, retinaldehyde and retinoic acid (preformed vitamin A) and a variety of carotenes and related compounds (collectively known as carotenoids), which can be cleaved oxidatively to yield retinaldehyde, and hence retinol and retinoic acid. Those carotenoids that can be cleaved to yield retinaldehyde are known as are known as pro-vitamin A carotenoids. 

The total amount of vitamin A in foods is expressed as ig retinol equivalents, calculated from the sum of Ig preformed vitamin A -F A X. lg P-carotene + /n X fig other pro-vitamin A carotenoids. 

As shown in Figure 11.3, P-carotene and other pro-vitamin A carotenoids are cleaved in the intestinal mucosa by carotene dioxygenase, yielding retinaldehyde, which is reduced to retinol, esterified and secreted in chylomicrons together with esters formed from dietary retinol. 

FIGURE 18.2 Names and structures of the fat-soluble vitamins and pro-vitamins A carotenoid naturally occurring in foods, (a) Vitamins A and D (b) vitamins E and K.p... 

Vegetarians will need to increase their intake of pro-vitamin A carotenoids in order to meet the recommended allowances. 

Scott, J.K. and Rodriquez-Amaya, D. (2000) Pro-vitamin A carotenoid conversion factors retinol equivalents - fact or fiction. Food Chem., 69, 125-127. 

A retinol equivalent is defined as 1 pg retinol, which is considered equal to 6 pg (3-carotene or 12 pg of mixed pro-vitamin A carotenoids. [28]. 

Breast-feeding and diet Dietary risk in children refers to inadequate breast-feeding combined with low intakes of VA-rich foods from the household diet. A low dietary fat intake (e.g., <5% of calories) may restrict absorption of pro-vitamin A carotenoids from vegetables and fruits and thus also predispose children to deficiency. 

Hypovitaminosis A is prevented by increasing intakes of preformed vitamin A or pro-vitamin A carotenoids to levels that maintain adequate status. This can be done through direct supplementation of targeted risk groups, food fortification, or a number of dietary approaches that protect breast-feeding and improve the quality of the home diet. 

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