Objective: To determine the vitamin A equivalence of spinach beta-carotene (beta-C) in human body.
Methods: Spinach grown in 25 atom% 2H2O cultural solution was intrinsically labeled by deuterium. The highest enrichment of spinach trans-beta-C isotopomers was at the molecular mass of 547 (2H10 trans-beta-C). Ten healthy Chinese male adults (43-56y) were given a dose of 5.8 micromol 13C10 retinyl acetate as vitamin A reference dose. One week later, each subject was given 100g of steamed spinach (containing 7.0 micromol beta-C). Forty blood samples were collected over 56 days from each subject. A HPLC method was used to detect the concentrations of retinol and beta-C in serum, and a GC-MS method was used to detect the enrichment of the labeled retinol. Kinetic curves of the labeled retinol from the reference dose and the spinach beta-C were compared to determine the vitamin A equivalence of spinach beta-C.
Results: The results showed that 1 nmol spinach beta-C provided (0.25 +/- 0.10) nmol retinol. The mean conversion factor of spinach beta-C to vitamin A was (9.0 +/- 4.5) : 1 by weight.
Conclusion: The bioconversion of spinach beta-C to vitamin A was determined in 10 Chinese male adults by stable isotope tracer and reference techniques, and the mean conversion factor was 9.0 to 1 on a weight basis.