一個國際單位相當于0.025微克的維生素D3，一微克的維生素D3有40國際單位.所以7.5微克的維生素d相當于300單位的維生素d。
1ug等于40單位的維生素d，7.5ug應該相當于300單位。我們每天維生素d的生理需要量，至少應該在400到600單位。
Vitamin A Technical Details:
Vitamin A is a fat-soluble vitamin. It is important for vision, bone growth and cell division.
Vitamin A consists ofRetinolfrom animal sources, andProvitamin A Carotenoidsfrom plant sources.
Retinol is referred to aspre-formedvitamin A. This means that it can be used directly by the body.
Provitamin A Carotenoids are Vitamin Aprecursors. This means that they are converted to Vitamin A by the body. However, conversion of the carotenoids is less efficient than that of retinol.
The Provitamin A Carotenoids are beta-carotene, alpha-carotene, beta-cryptoxanthin, lycopein, lutein and zeaxanthin (lutein and zeaxanthin are combined in the current database). The carotenoids are responsible for the red and yellow pigments of plants.
A unit called Retinol Activity Equivalents (RAE) is used to compare the Vitamin A activity of the different forms of Vitamin A. 1 μg (microgram) of retinol is equivalent to 1 μg RAE. However it takes 12 μg beta-carotene to equal 1 μg RAE, and 24 μg of the other carotenoids to equal 1 μg RAE. The following table summarizes the conversion of vitamin A values to RAE:
Historical Measures of Vitamin A
Previously, a unit called International Units (IU) was used to describe Vitamin A activity. However, at the time International Units for Vitamin A were defined (1989), it was thought that beta-carotene was half as concentrated as retinol (beta-carotene is now considered to be only 1/12 as concentrated as retinol).
Because of this, Vitamin A measurements expressed as IU tend to over-state the contribution of the provitamin A carotenoids. The following table summarizes the conversion of Vitamin A values to IU:
When it was determined that IU tended to overstate the contribution of the provitamin A carotenoids, a new unit called Retinol Equivalents (RE) was defined to describe the new values. At the time beta-carotene was thought to be 1/6 as concentrated as retinol. The following table describes the conversion of vitamin A values to RE:
In 2001, the National Academy of Sciences Institute of Medicine (NAS IOM) determined that Vitamin A activity from carotenoids is only half of what was previously believed. To account for this difference, and to avoid confusion, the new unit Retinol Activity Equivalents (RAE) was defined. Retinol Equivalents (RE) are no longer used.
The following table summarizes the relationship between the different measures:
At the time of this writing (2004), the RDI (Reference Daily Intake) of Vitamin A is 5000 IU. However, IU is an inaccurate measure of vitamin A activity because it overstates the contributions of the provitamin A carotenoids (by a factor of 6). The FDA (US Food and Drug Administration) is considering changing the RDI to express it in terms of RAE.
Because the conversion of IU to RAE is different for retinol and the carotenoids, you cannot convert IU to RAE (or RAE to IU) for Total Vitamin A unless you know the proportion of retinol to carotenoids in the sample.
For example, knowing that you have 40 IU of Total Vitamin A is not enough information to determine how much retinol and carotenoids you have. 40 IU of Total Vitamin A can come from 12 μg RAE of retinol, or from 2 μg RAE of carotenoids, or from 6 μg RAE retinol plus 1 μg RAE carotenoids, or from many other combinations of retinol and carotenoids. The following table summarizes:
nutraCosterDetails
Entering Retinol or Carotenoids Values
When you enter RAE for retinol or any of the carotenoids,nutraCosterautomatically calculates the IU and %RDI values for the nutrient.
Finally,nutraCosterwillrecalculate the IU and %RDI values of Total Vitamin A based on the new values for retinol and carotenoids.
Example: Suppose you have 80 μg RAE Total Vitamin A, which is composed of 60 μg RAE retinol and 20 μg RAE total carotenoids. The following table lists the values for the example:
Now change the Total Vitamin A RAE to 120 μg RAE.nutraCosterperforms the following steps:
Total Vitamin A RAE was the sum of the retinol and carotenoids values, sonutraCosterincreases retinol and carotenoids proportionally to 90μg RAE and 30 μg RAE.
The new value of 90 μg RAE for retinol converts to 300 IU and 6 %RDI.
The new value of 30 μg RAE for carotenoids converts to 600 IU and 12 %RDI.
Using the new IU and %RDI values, Total Vitamin A is now 900 IU and 18 %RDI.
The following table shows the results after the change:
nutraCosterperforms a similar series of steps when you enter IU or %RDI values for Total Vitamin A.
CarotenoidDetails
When you enter or change a value for Total Carotenoids,nutraCosterchecks to see if the Total Carotenoids value was equal to the sum of the individual Provitamin A Carotenoids before the change. If it was,nutraCosterrecalculates the individual carotenoid values so the sum of the values equals the new Total Carotenoids value, while keeping the proportions the same.
When you enter or change a value for any of the individual carotenoids,nutraCosterchecks to see if the Total Carotenoids value was equal to the sum of the individual Provitamin A Carotenoids before the change. If so,nutraCosteradjusts the Total Carotenoids value to equal the sum of the individual carotenoid values after the change.
為了統一計量膳食中的維生素A，而提出的一個概念。其含義是包括視黃醇和β-胡蘿卜素在內的具有維生素A活性物質所相當的視黃醇量。
由于人體維生素A來源于動物性食物的維生素A和植物性食物中的胡蘿卜素（維生素A原），而維生素A的常用計量單位為國際單位（IU），胡蘿卜素的常用計量單位為μg（微克）或者mg（毫克），為了統一計量膳食中的維生素A，FAO/WHO（1967）提出了視黃醇當量（Retinol Equivalent, RE)概念。其含義是包括視黃醇和β-胡蘿卜素在內的具有維生素A活性物質所相當的視黃醇量。
1μg β-胡蘿卜素=0.167μg視黃醇當量（理論上1分子β-胡蘿卜素能形成2分子維生素A，但因為胡蘿卜素的吸收率為1/3，而吸收后轉化為維生素A的轉化率又只有1/2，所以，1μg的胡蘿卜素只能折算為0.556IU維生素A，即0.167μg視黃醇當量。1IU維生素A=0.3μg視黃醇當量）
