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

Abstract

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%2H2O nutrient solution. Growth in this medium yielded a range of trans β-carotene (tβ-carotene) isotopomers 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/m2) of 25.7 ± 1.5 consumed puréed spinach (300 g, 20.8 μmoltβ-carotene equivalents) or carrots (100 g, 19.2 μmol tβ-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 puréed spinach only (300 g, 20.0 μmol tβ-carotene equivalents). A reference dose of [13C8]retinyl acetate (8.9 μmol) 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 β-carotene responses were 42.4 ± 8.5 nmol · d per μmol spinach β-carotene and 119.8 ± 23.0 nmol · d per μmol carrot β-carotene (P < 0.01). Compared with the [13C8]retinyl acetate reference dose, spinachtβ-carotene conversion to retinol was 20.9 ± 9.0 to 1 (range: 10.0–46.5 to 1) and carrottβ-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.