Carotene retinol equivalents

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). 

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... 

The biological activities of vitamin A and previtamin A are not equivalent on a per-weight basis. In humans, 6.0 mg of p-carotene is equivalent to 1.0 mg of retinol. Twelve milligrams of the other carotenoids is equivalent to 1-0 mg of retinol. The relatively low biological activity of the carotenoids is due to the inefficiency in their conversion to retinol and their ioivet availability u/beti present in foods. When -carotene is provided in pure form (dissolved in some oil and swallowed) its value is still less than that of vitamin A, Here, 2.0 mg of p-carotenc is equivalent to l.O mg of retinol. 

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."... 

The best documented and established function of some carotenoids is their provitamin A activity, especially of P-carotene. One mole of P-carotene can theoretically be converted, by cleavage of C 15 = C 15 double bond, to yield two moles of retinal (Reaction 9.1). However, the physiological efficiency of this process appears to be only 50%. The observed average efficiency of intestinal P-carotene absorption is only two thirds of the total content. Thus, a factor of 1/6 is used to calculate the retinol equivalent (RE) from P-carotene, but only 1/12 from the other provitamin A carotenoids in food (Combs, 1992). In fruits and vegetables P-carotene content is used as a measure of the provitamin A content. 

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. 

Retinol equivalents. 1 retinol equivalent = Ipg retinol or 6 pg -carotene. 

RE = retinol equivalent, where 1 retinol equivalent = 1 j,g retinol or 6 j,g p-carotene. See Section 8.7. 

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. 

The stoichiometry of conversion of /3-carotene to retinol is still an unsettled issue. Central cleavage of /3-carotene theoretically yields 2 mol retinol per mole /3-carotene (Goodman and Huang, 1%5 Olson and Hayaishi, 1965 Olson, 1989) and eccentric cleavage of /3-carotene yields 1 mol retinol per mole /3-carotene (Olson, 1989, Krinsky et al., 1994). Brubacher and Weiser (1985) determined the retinol equivalent of /3-carotene in vivo using rats and chicks and found that 1 mol of absorbed /3-carotene yielded 1 mol retinol. Because the body reserves of retinol in these animals were low, the yield of retinol from /3-carotene was probably maximal. Based on these in vivo results, a ratio of 1 mol retinol per mole /3-carotene (after absorption) was used in constructing the present compartmental model of the dynamics of /3-carotene metabolism. 

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... 

Lemke SL, Dueker SR, Follett JR, Lin YM, Carkeet C, Buchholz BA, Vogel JS, Clifford AJ. Absorption and retinol equivalence of beta-carotene in humans is influjenced by dietary vitaman A intake. J Lipid Res 2003 44(8) 1591 —1600. 

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). 

Retinol equivalents = xg retinol + xg p-carotene x 0.167 + xg other provitamin carotenoids X 0.083. For comparison with values in the older literature, the equivalent lU values of retinol can be calculated by multiplying the RE values by 3.33. For examples of the application of these formulas to the evaluation of diets, the reader is referred to the 9th edition of the Recommended Dietary Allowances (Food and Nutrition Board, 1980). 

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