Some Important Facts about Vitamin A

Vitamin A is actually retinol. However, for practical purpose it also include a pro vitamin, pre formed vitamin, beta-carotene, retinoic acids, retinaldehyde, and oxidized metabolites etc. other than retinol. Some of the above are converted to retinol in the intestinal mucosa. The term retinoid include all the molecules that are chemically related to retinol. Retinaldehyde is the essential form of vitamin A that is required for normal vision and retinoic acid is necessary for normal morphogenesis, growth, and cell differentiation in our body.

The unit of vitamin A at present is “retinol activity equivalent” (RAE) and this is very convenient to use than the older form of IU (international unit). IU was in use before 1954 and after 1960 the unit “retinol” is used for vitamin-A alcohol that is available in crystalline form. 1 IU of vitamin A is equal to 0.03 microgram (mcg) of retinol. The following is the conversion:

1 microgram of retinol = to 1 mcg of RAE

1 mcg of carotinoid (beta carotene) = 0.084mcg of RAE

Vitamin A is commercially available in esterified forms (e.g., acetate, palmitate), because they are more stable forms of vitamin A.

There are more than 600 carotinoids available in the nature and out of that about 50 of them can be converted to or metabolized to vitamin A. Beta carotene is the commonest form of carotinoid that is available in our food with pro vitamin activity. In humans large percentage of carotinoids are absorbed and stored in liver and fat deposits.


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