A provitamin is a substance that may be converted within the body to a
vitamin
A vitamin is an organic molecule (or a set of molecules closely related chemically, i.e. vitamers) that is an essential micronutrient that an organism needs in small quantities for the proper functioning of its metabolism. Essential nut ...
.
The term previtamin is a synonym.
The term "provitamin" is used when it is desirable to label a substance with little or no vitamin activity, but which can be converted to an active form by normal
metabolic
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cel ...
processes. Some provitamins are:
* "Provitamin A" is a name for
β-carotene,
[ which has only about 1/6 the biological activity of retinol (]vitamin A
Vitamin A is a fat-soluble vitamin and an essential nutrient for humans. It is a group of organic compounds that includes retinol, retinal (also known as retinaldehyde), retinoic acid, and several provitamin A carotenoids (most notably ...
); the body uses an enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...
to convert β-carotene to retinol. In other contexts, both β-carotene and retinol are simply considered to be different forms ( vitamers) of vitamin A.
* "Provitamin B5" is a name for panthenol, which may be converted in the body to vitamin B5 ( pantothenic acid).
* Menadione is a synthetic provitamin of vitamin K
Vitamin K refers to structurally similar, fat-soluble vitamers found in foods and marketed as dietary supplements. The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulat ...
.
* Provitamin D2 is ergosterol, and provitamin D3 is 7-dehydrocholesterol. They are converted by UV light into vitamin D.[ The human body produces provitamin D3 naturally; deficiency is usually caused by a lack of sun exposure, not a lack of the provitamin.]
References
Vitamins
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