Carotenoids retinol equivalent activity

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. 

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). 

Adults— The FNB-NRC recommended daily allowance of vitamin A for adult men is set at 1,000 meg RE (3,333 lU). The allowance is based on the assumption that the average American diet provides half the total vitamin A activity as retinol and half as provitamin A carotenoids. In terms of Retinol Equivalents (RE), this is 750 meg retinol (1 RE = 3.33 lU retinol) and 250 Retinol Equivalents as beta-carotene (1 RE = 10 lU beta-carotene) for a total of 1,000 RE. 

Prior to 2001, the retinol equivalent (RE) was used and this unit is still found in most food composition tables. While similar in theory to the RAE, the RE is based on older conversion factors for carotenoids in foods. Using RAE, the vitamin A activity of the provitamin A carotenoids in foods is half that using RE. An older unit, the international unit (lU or USP), which should eventually be replaced by these newer units, is still used in food tables and on some supplement labels. One lU is equal to 0.3 pg of all-fra/M-retinol. Finally, another indicator of nutritional value, % daily value (%DV), is a less quantitative but more convenient means for consumers to compare foods and select those with a substantial portion of a given nutrient. The %DV does not require extensive knowledge of nutritional units this value appears on food package labels in the US. Besides its application in food labeling, the %DV is a useful value for quickly comparing the vitamin A contents of various common foods. 

The U.S./Canadian Dietary Reference Values report (Institute of Medicine, 2001) introduced the term retinol activity equivalent to take account of the incomplete absorption and metabolism of carotenoids 1 RAE = 1 /xg of all-fra s-retinol, 12 /xg of /3-carotene, and 24 /xg of a-carotene or /3-crypto-xanthin. On this basis, 1 iu of vitamin A activity = 3.6 /xg of /3-carotene or... 

Institute of Medicine to recommend the retinol activity equivalent (RAE) as the basis of calculation of retinol intake. In this system, a ratio equivalence of 1 12 24 is recommended (i.e., 12jLlg p-carotene or 24 Ug mixed carotenoids has the same biological activity as IjLig retinol). Using this system, current RDAs for vitamin A are 900 pg RAE for men 19 years and older 700 ug RAE for women 19 years and older, with up to 770 xg RAE/day in pregnancy and up to 1300 fig RAE/day in lactation 300 to 900 fig RAE for children 1 to 18 years, dependent upon age and sex and for infants an adequate intake (AI) of 400 fig RAE at 0 to 6 months and 500 fig RAE from 7 to 12 months. ... 

Some 50 or more dietary carotenoids are potential sources of vitamin A a-, P- and y-carotenes and cryptoxanthin are quantitatively the most important. Although it would appear from its structure that one molecule of P-carotene will yield two of retinol, this is not so in practice (section 11.2.2.1) 6 ig of P-carotene is equivalent to 1 Ig of preformed retinol. For other carotenes with vitamin A activity, 12 J,g is equivalent to 1 Ig of preformed retinol. 

Owing to the multiple forms of vitamin A in most diets and the lower efficiency of utilization of carotenoids compared to preformed vitamin A, the total amount of vitamin A (bioactivity) in foods or in the total diet must be expressed in equivalents. Over the years, several equivalency units and conversion factors have been adopted. Most recently, the retinol activity equivalent was adopted by the Institute of Medicine (lOM) in 2001 to replace older units of bioactivity because new information indicated that the conversion of carotenoids is less... 

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