Bioequivalence of β‐carotene and retinol

Abstract

For many years it was accepted that 6 mg of β-carotene were required to produce 1 mg of vitamin A in the form of retinol. The equivalence was based on the assumptions that two-thirds of dietary β-carotene are not absorbed, while in the metabolism of the remaining third 1 mol of β-carotene is converted to 1 mol retinol. Recently, the bioequivalence was raised to 12 mg β-carotene and 1 mg retinol. The objective of this review was to re-examine the data that were used to support the new equivalence ratio, especially since some of these data were obtained in developing countries where infestation with gut parasites and exposure to other infections is common, yet the influence of inflammation on plasma carotenoid and retinol concentrations is frequently ignored. Bioequivalence studies examined in this review include those done in developing and developed countries, depletion and repletion studies, feeding with vegetable sources of β-carotene or pure supplements, influence of helminths, carotenoid interactions and matrix effects and studies using stable isotopes (SI). SI studies show the bioefficacy of β-carotene conversion to retinol is generally poor even for pure β-carotene unless the dose is small and fed regularly until equilibration is reached. Retinol formation appears to be inversely influenced by previous vitamin A intake, the amount of material given and current vitamin A status. In spite of technical complexities, more SI studies where liver reserves of vitamin A are determined pre and post intervention are needed to evaluate β-carotene bioefficacy of different vegetable sources.

Carotenoids bioavailability from foods: From plant pigments to efficient biological activities

“…This last unit has emerged to replace the RE and correct the overestimation of bioefficacy. All these aspects have recently been reviewed by Thurnham (2007).…”

Degradation of β-carotene during fruit and vegetable processing or storage: reaction mechanisms and kinetic aspects: a review

“…These compounds may lower the sensory and nutritional properties of the resulting food products. For instance, it was demonstrated that the cis-isomers of β-carotene have lower antioxidant properties than trans-β-carotene [3] and generate about two-fold less vitamin A [20]. In addition, some studies reported the increase in oxidative stress caused by end products of carotene β-oxidation [21].…”

THE EFFECT OF Sauropus androgynus LEAF EXTRACT ON PERFORMANCE, EGG QUALITY AND CHEMICAL COMPOSITION OF EGGS

“…β-carotene is converted to retinal in the intestinal mucosa, then to retinol (vitamin A). The key step for vitamin A formation is the oxidative cleavage of provitamin A carotenoids by β-carotene15,15-dioxygenase (Thurnham, 2007).…”