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Spinach or carrots can supply significant amounts of vitamin A as assessed by feeding with intrinsically deuterated vegetables^1,2,3,4

¹ From the Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, MA (GT, JQ, GGD, and RMR), and the US Department of Agriculture/Agricultural Research Service, Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, TX (MAG)

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 ß-carotene (tß-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 µmol tß-carotene equivalents) or carrots (100 g, 19.2 µmol tß-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 tß-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 ß-carotene responses were 42.4 ± 8.5 nmol · d per µmol spinach ß-carotene and 119.8 ± 23.0 nmol · d per µmol carrot ß-carotene (P < 0.01). Compared with the [¹³C₈]retinyl acetate reference dose, spinach tß-carotene conversion to retinol was 20.9 ± 9.0 to 1 (range: 10.0–46.5 to 1) and carrot tß-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.

Key Words: Vegetables • stable isotope • hydroponics • spinach • carrots • mass spectrometry

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