The vitamin A activity of beta-carotene.

In rats (parameters: growth, epithelial protection and liver storage), and in chicks (liver storage), it has been demonstrated that the conversion of beta-carotene to vitamin A diminishes inversely to the intake of beta-carotene, as long as the dosages are higher than 1-2 times the daily requirements. The decrease in the biopotency of beta-carotene follows a Michaelis Menten kinetic. In the dosage range of the daily requirements molecular ratio applies. Based on these findings, the following guidelines for the conversion of retinol in man are proposed: (Table: see text). For beta-carotene in oily solutions, a conversion factor of 1:3.33 should be accepted for the dosage range of 1,500 to 4,000 micrograms. For higher doses, this factor should be decreased according to the results with laboratory animals: For beta-carotene in vegetables, the conversion factor of 1:6.0 should be accepted for intakes between 1,500 and 4,000 micrograms. A higher factor should be chosen for smaller intakes, and a smaller factor for higher intakes.