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A. Where values for vitamin A were expressed in terms of International Units (I.U.), to convert to micrograms the following factors were applied:

One International Unit (I.U.) = 0.3 mcg. of retinol
 = 0.6 mcg. of beta-carotene
 = 1.2 mcg. of other total mixed carotenoids with vitamin A activity

Where values were expressed in micrograms of vitamin A activity, for conversion of micrograms of retinol, beta-carotene and other carotenoids to a common denominator of micrograms of retinol, the following factors were employed:

One mcg. of vitamin A value = 1 mcg. of retinol
One mcg. of beta-carotene = 0.5 mcg. of retinol
One mcg. of other total mixed carotenoids = 0.25 mcg. of retinol

The following illustrations for conversion of International Units into retinol and B-carotene equivalent are taken directly from the FAO/WHO Expert Group Report on “Requirements of Vitamin A, Thiamine, Riboflavine and Niacin,” page 78:

Conversion of International Units of Vitamin A in Foods to Retinol and B-Carotene Equivalent

1. Papaya has 425 I.U. vitamin A value, with 85 percent of B-carotene and 15 percent the other carotenoids

then, it has 425 × 85 percent = 361 I.U. of B-carotene
or,425 × 15 percent = 64 I.U. of other carotenoids
  361 × .6 = 217 mcg. B-carotene
 64 × 1.2 = 76.8 mcg. other carotenoids
but, 1 mcg. B-carotene = 2 mcg. other carotenoids
therefore= 255 mcg. B-carotene in papaya

The same result can be obtained by multiplying 425 by 0.6.

2. A sample of milk has 130 I.U. of vitamin A value: 70 percent is retinol and 30 percent is B-carotene

then, it has 130 × 70 percent = 91 I.U. of retinol
 130 × 30 percent = 39 I.U. of B-carotene
and therefore, 91 × .3 = 27.3 mcg. retinol, and
 39 × .6 = 23.4 mcg. B-carotene

3. Lean meat has 50 I.U. of vitamin A per 100 grams: 90 percent is retinol and 10 percent is B-carotene

then, it has 50 × 90 percent = 45 I.U. of retinol
 50 × 10 percent = 5 I.U. of B-carotene
and therefore, 45 × .3 = 13.5 mcg. retinol, and
 5 × .6 = 3 mcg. B-carotene

B. Estimated Distribution of Sources of vitamin A Activity in Various Foods

 From RetinolFrom Retinol Precursors
Beta-caroteneCarotenoids other than Beta
Animal origin:   
Meat and meat organs9010 
Fish and Shellfish9010 
Milk and Milk Products7030 
Animal or fish oil9010 
Plant origin:   
Maize, yellow 4060
Others 5050
Legumes and seeds 5050
Green vegetables 7525
Deep yellow (carrots, sweet-potatoes-deep orange type, etc.) 8515
Sweetpotato--pale type 5050
Other vegetables 5050
Deep yellow (a pricot, sapote, etc.) 8515
Other fruits 7525
Vegetable oils:   
Red palm oil 6535
Other vegetable or seed oils 5050

C. Comparison of Intakes as Calculated from the Present Table with Vitamin A Requirements can be made by the following methods:

  1. Add the retinol values (mcg.) of the different foods consumed;

  2. Do the same operation in a separate column for B-carotene (mcg.);

  3. The utilization efficiency of B-carotene being only 0.167, 1 multiply the B-carotene intake by 0.167 (or divide by 6) in order to obtain the equivalence expressed in mcg. of retinol;

  4. Add mcg. of retinol (1) and mcg. of retinol equivalent (3);

  5. Compare this intake with the requirements expressed in mcg. of retinol.

1 Sources: Requirements of vitamin A, thiamine, ribofiavine and niacin. A report of a Joint FAO/WHO Expert Group, September 1965. FAO Report Ser. No. 41, 1967.

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