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 Retinol | From Retinol Precursors | ||
|---|---|---|---|
| Beta-carotene | Carotenoids other than Beta | ||
| Animal origin: | |||
| Meat and meat organs | 90 | 10 | |
| Poultry | 70 | 30 | |
| Fish and Shellfish | 90 | 10 | |
| Eggs | 70 | 30 | |
| Milk and Milk Products | 70 | 30 | |
| Animal or fish oil | 90 | 10 | |
| Plant origin: | |||
| Cereals: | |||
| Maize, yellow | 40 | 60 | |
| Others | 50 | 50 | |
| Legumes and seeds | 50 | 50 | |
| Vegetables: | |||
| Green vegetables | 75 | 25 | |
| Deep yellow (carrots, sweet-potatoes-deep orange type, etc.) | 85 | 15 | |
| Sweetpotato--pale type | 50 | 50 | |
| Other vegetables | 50 | 50 | |
| Fruits: | |||
| Deep yellow (a pricot, sapote, etc.) | 85 | 15 | |
| Other fruits | 75 | 25 | |
| Vegetable oils: | |||
| Red palm oil | 65 | 35 | |
| Other vegetable or seed oils | 50 | 50 | |
C. Comparison of Intakes as Calculated from the Present Table with Vitamin A Requirements can be made by the following methods:
Add the retinol values (mcg.) of the different foods consumed;
Do the same operation in a separate column for B-carotene (mcg.);
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;
Add mcg. of retinol (1) and mcg. of retinol equivalent (3);
Compare this intake with the requirements expressed in mcg. of retinol.
