Retinol equivalent

Furusho T, Kataoka E, Yasuhara T, Wada M and Masushige S. 2000. Retinol equivalence of carotenoids can be evaluated by hepatic vitamin A content. Int J Vitam Nutr Res 70 43-47. 

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

The liver of meat animals is a rich source of vitamin A, for this organ is the body s main storage site of the vitamin. Fish liver oils, particularly halibut liver oil, are incredibly rich in the vitamin and are too potent to be consumed as foods. Typical food sources of vitamin A (in /ag retinol equivalents/100 g) are sheep and ox liver, 15,000 butter, 830 cheese, 320 eggs, 140 herring and... 

The vitamin A value of foods has traditionally been expressed in international units (IU). One IU is defined as the amount of vitamin A activity contained in 0.334 fig of all-trans-retinyl acetate, which is equivalent to 0.300 fig of alRran.v-retinol. In 1965, an expert committee decided to abandon the IU for vitamin A, proposing instead that the vitamin A value be designated in terms of retinol equivalents (RE), expressed in micrograms of retinol. The RE is defined as the amount of retinol present plus the equivalent amount of retinol that can be obtained from the provitamins. It is purely a dietary concept and is not an equivalency in the usual chemical sense ... 

For comparison with values in the older literature, the IU values can be converted to retinol equivalents. To convert IU into RE on the basis of retinol, 1 RE = 1 fig retinol and 1 IU = 0.3 fig retinol. Therefore, 1 RE = 1/0.3 = 3.33 IU vitamin A activity from retinol. 

For food labeling purposes, which require the actual amounts of vitamin A in the food rather than the nutritional value, data obtained by physicochemical assay are expressed on a weight basis. In plant-derived foods, the appropriate units are /3-carotene equivalents expressed in micrograms of /3-carotene. By definition, 1 /3-carotene equivalent is equal to 1 fig of all-trans-/3-carotene or 2 fig of other, largely animal-derived foods, the units are either micrograms of retinol or retinol equivalents (32). 

Table 3 International Units (IU) and Retinol Equivalents (RE) for Expressing Vitamin A Values in Humans...

T ble 7 Clinical/epidemiological studies using /3-carotene. Dosage is reported also in terms of pig retinol equivalents (RE) ... 

The vitamin A content of foods is often given in terms of the international unit (IU). One IU of vitamin A is defined as 0.3 tg of all-trans-retinol. The term retinol equivalent (RE) is used to convert all sources of vitamin A and carotenoids in the diet to a single unit. One RE is by definition 1 pg of all-trans retinol, 12 pg of P-carotene, or 24 pg of other (mixed) provitamin A carotenoids. The recommended dietary allowance for vitamin A ranges from 375 pg RE/day for infants to 1,000 RE/day for adults. 

One of the highest known concentrations of carotenoids occurs in crude palm oil. It contains about 15 to 300 times more retinol equivalent than carrots, green leafy vegetables, and tomatoes. All of the carotenoids in crude palm oil are destroyed by the normal processing and refining operations. Recently, improved gentler processes have been developed that result in a red palm oil that retains most of the carotenoids. The composition of the carotenes in crude palm oil with a total carotene concentration of 673 mg/kg is shown in Table 6-5. 

To take account of the contribution from carotenoids, the total vitamin A content of foods is expressed as micrograms of retinol-equivalents - the sum of that provided by retinoids and from carotenoids. Because of the relatively low absorption of carotenes and incomplete metabolism to yield retinol (Section 2.2.2), 6 /xg of /3-carotene is 1 jxg of retinol-equivalent - a molar ratio of... 

Since then, eight more subjects have been studied (Sauberlich et al., 1974 Hodges etal., 1978). From these studies, the reference intake for adult men was set at 1,000 /rg of retinol equivalent, with a minimum physiological requirement of 600 /rg per day. Because the signs of deficiency only resolve slowly, it is possible that depletion/repletion studies overestimate requirements. 

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