|Identification of Food Components for INFOODS Data Interchange (UNU, 1989, 165 pages)|
|4. Assigning the correct food component tagnames to the nutrient data|
Nutrient values labelled "vitamin A" in different food composition tables and nutrient data bases may represent different portions of the total vitamin A activity in a food. Therefore, it is essential to know what is included in a particular "vitamin A" value before a tagname is assigned to that value.
Total vitamin A includes both retinol (also called "preformed vitamin
A") and carotene (also called "vitamin A precursor"). Total
vitamin A is usually calculated as the total vitamin A activity contributed by
retinol, beta-carotene, and other active carotenoids. This calculated value is
expressed in retinol equivalents (RE) and is sometimes referred to simply as
"retinol equivalents". It is calculated according to the following
total vitamin A (RE) = mcg of retinol + 1/6 mcg of beta-carotene + 1/12 mcg of other active carotenoids
Total vitamin A may also be determined directly by bioassay and expressed in international units (IU). The tagnames for identifying total vitamin A values distinguish between those values that were calculated from retinol and the active carotenoids and those determined by bioassay. A tagname is also available for use when the method of vitamin A determination is not known. These three tagnames are listed below. All are subsidiary to the <comp> structural tag.
|<VITA>||vitamin A; calculated by summation of the |
vitamin A activities of retinol and the active
|<VITAA>||vitamin A; determined by bioassay|
|<VITA->||vitamin A; method of determination unknown|
<VITA> values are usually expressed in retinol equivalents, and <VITAA> values are usually expressed in international units. However, a value expressed in one unit may be converted to the other unit according to the following formulae:
1 mcg retinol = 3.3 IU of retinol
1 RE from beta-carotene = 10 IU of beta-carotene
Beta-carotene equivalents (also called "provitamin A carotenoids")
are a measure of the vitamin A activity contributed by the active carotenoids.
As indicated in the above formula for calculating vitamin A in retinal
equivalents, beta-carotene has twice the vitamin A activity of the other active
carotenoids. Therefore, beta-carotene equivalents are calculated according to
the following formula:
mcg of beta-carotene equivalents = mcg of betacarotene + 1/2 the mcg of other active carotenoids
The tagname for beta-carotene equivalents is listed below, as are the tagnames for identifying data on the retinol and active carotenoid components that can contribute to the calculated total vitamin A value. All are subsidiary to the <comp> structural tag.
|< CARTBEQ >||beta-carotene equivalents|
|< CARTA > |
< CARTB >
< CARTG >