A provitamin is a substance that may be converted within the body to a vitamin.^[1] The term previtamin is a synonym.^[2]

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 processes.^{[citation needed]}

Some provitamins are:

• "Provitamin A" is a name for β-carotene,^[1] which has only about 1/6 the biological activity of retinol (vitamin A); the body uses an enzyme 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.
• Provitamin D₂ is ergosterol, and provitamin D₃ is 7-dehydrocholesterol. They are converted by UV light into vitamin D.^[1] The human body produces provitamin D₃ naturally; deficiency is usually caused by a lack of sun exposure, not a lack of the provitamin.^[3]