Vitamin retinol equivalents

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...

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. 

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... 

Vitamin A activity can be expressed either as international units lU (1 lU equaling 0.3 micrograms of aH-trans-retinol or 0.6 micrograms of all-trara-beta-carotene) or, more correctly, in retinol equivalents (RE) where 1 RE equals 1 microgram of all-trara-retinol, 6 micrograms of all-trara-beta-carotene or 12 micrograms of other provitamin A carotenoids. Table 1 gives the activities of different forms of vitamin A in RE and lU. 

Vitamin A activity is expressed as USP units, international units (lU). retinol equivalents (RE), and arotene equivalents. The USP units and lU are equivalent. Each unit ex-pre.sses the activity of 0.3 /ug of all-/rans-retinol. Thus. I mg of all-/rufis-retinol has the activity of 3.333 unit.s. Other equivalents are li.sted in Table 26-3. One RE represents the biological activity of I /7g of all-rnin.t-relinol, 6 /ug of carotene. and 12 /rg of mixed dietary carotenoids. The RE i.s u.sed to convert all dietary sources of vitamin A into a single unit for easy comparison."... 

Ingestion of vitamin A in large excess of the RDA can cause toxicity. Daily intake of more than 7500 retinol equivalents (25,000 lU) is not recommended, and doses in excess of 3000 retinol equivalents (10,000 lU) should only be used with medical supervision. Acute toxicity after... 

Retinol equivalents. 1 retinol equivalent =1 fig of retinal or 6 ftg of -carotene. llAs cholecalciferol. 10 pg of cholecalciferol = 400 lU of vitamin D. 

Food Category Vitamin A Retinol Vitamin D Equivalent (pg) (pg) Vitamin E Tocopherol Equivalent (mg) Vitamin K... 

Concerning the fat-soluble vitamins, the range of RDA value of vitamin E is 5-50 mg of a-tocopherol equivalent per day, the median 10 mg/day. The RDA value of vitamin A is 360-1650 gg/day of retinol equivalent (RE) with the median of 800 RE/day. As mentioned before, seaweed does not contain intrinsic vitamin A, but its provitamins, with p-carotene as the most abimdant. The relevant dose of p-carotene intake is about 15 mg/day (Krinsky, 1998). The vitamin A activity (gg RE/100 g) is recalculated from determined content of p-carotene. 

As retinol activity equivalents (RAEs). 1 RAE = 1 pg retinol, 12 pg p-carotene, 24 pg a-carotene, or 24 pg p-cryptoxanthin. The RAE for dietary provitamin A carotenoids is twofold greater than retinol equivalents (RE), whereas the RAE for preformed vitamin A is the same as RE As cholecalciferol. 1 pg cholecalciferol = 40 lU vitamin D Under the assumption of minimal sunlight... 

Lycopene is one of the most widely consumed carotenoids however, it lacks provitamin A activity. Through cyclisation at one or both end groups of lycopene, carotenes are formed, containing one (8 and 7 carotenes) or two a and 3 carotenes) ionone rings. Vitamin A (all-tmns-retinol) consists of a (3-ionone ring with a side chain of three isoprenoid units. Hence a and 3 carotenes provide two molecules of retinol in the human body whereas 8 and 7 carotenes provide only one. In reality, carotenoids are incompletely absorbed and 6 jLg of p carotene is equivalent to 1 pg retinol equivalent (RE). Carotenoids with hydroxylated ionone rings (e.g. lutein) provide no vitamin A activity (Eitenmiller and Landen 1999). 

Effect of Dietary Source of Retinol Equivalents (RE), Preformed versus Precursor, on Plasma Levels of Vitamin A and Carotenoids in Senegal" and the United States ... 

Nieman and Obbink (1954) have provided an extensive review of the subchronic toxicity of vitamin A preparations and of retinol that appeared in the literature up to the early 1950s. The studies described were carried out in a variety of animal species but primarily in the rat dosages ranged from 3 to 180 mg retinol equivalents/day and the duration of treatment varied from a few days to several weeks. 

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