Vitamin A potency of carrot and spinach carotenes in human metabolic studies.

Changes in plasma retinol and carotenoids was measured in 17 young males after daily ingestion of grated carrots, carrot juice or spinach leaves for 2 weeks. Regression equations showed that the supply of 3350 and 4750 micrograms carotenes from 78 ml carrot juice (prepared from 185 g carrots) or 91 g grated carrots, respectively were adequate in maintaining plasma retinol at a constant level in subjects with initial plasma retinol of 1.2 mumol/l. Under similar experimental conditions, 280 g boiled spinach leaves providing 12,700 micrograms carotenes were required to maintain plasma retinol at a constant level. Apparent carotene digestibilities of 47 and 81% were obtained with carrot and spinach, respectively.