Food Data Chart - Vitamin A



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- Fat-Soluble Vitamins -

11: VITAMIN A

Some foods contain both vitamin A itself, and other substances that can be converted to vitamin A, known as provitamin A, vitamin A precursors or carotenoids . Although it is possible to have a toxic amount of preformed vitamin A, this appears not to be the case with provitamin A, so that it is clearly safer to have more of the latter.

Vitamin A is a fat-soluble vitamin, as also are vitamins D, E and K. It is therefore necessary to have some fat in the diet for these vitamins to be adequately absorbed.

One of the most important consequences of vitamin A deficiency is dryness of the eyes eventually leading to blindness. It remains one of the main causes of blindness in the world. Night blindness is also an eye complication of early vitamin A deficiency.

UNITS OF VITAMIN A CONTENT

The units for expressing the amount of vitamin A have changed from time to time because of the need to consider both preformed vitamin A (called retinol) and provitamin A (a group of components called carotenoids, of which beta-carotene is the most active and the most important). The present custom is to express the total amount of vitamin A activity as equivalent to so many micrograms of retinol. But some vitamin preparations may express the amount of vitamin A in different ways, so to help you compare these a list of conversion factors are given below:

1 retinol equivalent = 1 microgram retinol
= 6 micrograms beta-carotene

= 12 micrograms of other provitamin A carotenoids.

The original system using international units (IU) was different, so:

1 retinol equivalent = 3.33 I-U vitamin A activity from retinol
= 10 IU vitamin A activity from beta-carotene.

VITAMIN A INTAKE


Recommended dietary intake of vitamin A for adults (Australia):

750 micrograms of retinol equivalents per day. For children and lactating women, see the table of recommended intakes shown in Figure 7.

Toxic levels of intake:

Children - greater than 3000 micrograms retinol equivalents per day Adults - greater than 15 000 micrograms retinol equivalents per day