Spinach or carrots can supply significant amounts of vitamin A as assessed by feeding with intrinsically deuterated vegetables

Background: The vitamin A value of spinach and carrots needs to be measured directly. Objective: The objective was to determine the vitamin A value of intrinsically labeled dietary spinach and carrots in humans. Design: Spinach and carrots were intrinsically labeled by growing these plants in 25 atom% (H2O)-H-2 nutrient solution. Growth in this medium yielded a range of trans beta-carotene (t beta-carotene) isotoporners with a peak enrichment at molecular mass plus 10 mass units. Seven men with a mean (+/- SD) age of 59.0 +/- 6.3 y and a body mass index (in kg/m(2)) of 25.7 +/- 1.5 consumed pureed spinach (300 g, 20.8 mu mol t beta-carotene equivalents) or carrots (100 g, 19.2 mu mol t beta-carotene equivalents) with a standardized liquid diet (no extra fiber) in random order 4 mo apart. Seven women with a mean ( SD) age of 55.5 +/- 6.3 y and a body mass index of 26.4 +/- 4.2 consumed pureed spinach only (300 g, 20.0 mu mol to-carotene equivalents). A reference dose of[(13)C8]retinyl acetate (8.9 mu mol) in oil was given to each subject 1 wk after each vegetable dose. Blood samples were collected over 35 d. Results: Areas under the curve for total labeled serum beta-carotene responses were 42.4 +/- 8.5 nmol (.) d per mu mol spinach beta-carotene and 119.8 +/- 23.0 nmol (.) d per mu mol carrot beta-carotene (P < 0.01). Compared with the [C-13(8)]retinyl acetate reference dose, spinach to-carotene conversion to retinol was 20.9 +/- 9.0 to 1 (range: 10.0-46.5 to 1) and carrot to-carotene conversion to retinol was 14.8 +/- 6.5 to 1 (range: 7.7-24.5 to 1) by weight. Conclusions: Spinach and carrots can provide a significant amount of vitamin A even though the amount is not as great as previously proposed. Food matrices greatly affect the bioavailability of plant carotenoids, their efficiency of conversion to vitamin A, or both.