Provitamin

Provitamins are precursors of vitamins and must first be converted into these in order to be of benefit to the body. Since the body only ever converts as many provitamins into vitamins as needed, provitamins cannot cause poisoning.

Examples of provitamins include beta-carotene, a precursor of vitamin A, and 7-dehydrocholesterol, which is converted into vitamin D3 (cholecalciferol) in the skin by sunlight.