provitamin

A provitamin is a substance that is not itself a vitamin but can be converted by the body's metabolism into an active vitamin. The concept helps explain why some foods provide vitamin activity beyond their direct vitamin content, since their compounds must be transformed for use by the body.

The best-known provitamins are provitamin A carotenoids, such as beta-carotene, alpha-carotene, and beta-cryptoxanthin, found in colorful fruits and vegetables. These compounds can be converted to vitamin A (retinol) in the intestinal lining and liver, although conversion efficiency varies among individuals, influenced by genetics, health, and intake. For this reason foods containing provitamin A carotenoids are often described in terms of retinol activity equivalents (RAE).

In relation to vitamin D, certain sterols act as provitamins. 7-dehydrocholesterol in the skin is transformed into vitamin D3 after exposure to ultraviolet B radiation. Ergosterol and related compounds in fungi and yeasts can be converted to vitamin D2 under UV light. These examples illustrate how provitamins differ across vitamins and organisms.

In nutrition literature, provitamin terminology is most commonly applied to fat-soluble vitamins, particularly vitamin A and vitamin D precursors. Not all nutrients have recognized provitamins, and the degree of conversion to the active vitamin can vary widely between individuals and conditions.