Vitamin A equivalence of spirulina [beta]-carotene in Chinese adults as assessed by using a stable-isotope reference method

Background: Spirulina is a high-protein food supplement that contains carotenoids. Objective: The objective of the study was to determine the vitamin A equivalence of spirulina [beta]-carotene in humans. Design: Spirulina was grown in a 23 atom% [sup.2][H.sub.2]O cultural solution. Spirulina [beta]-carotene showed the greatest enrichment as [[sup.2][H.sub.10]]trans [beta]-carotene. Ten healthy Chinese men with a mean ([+ or -]SD) serum retinol concentration of 1.7 [+ or -] 0.3 [micro]mol/L and a body mass index (in kg/[m.sup.2]) of 23 [+ or -] 3 consumed 5.8 [micro]mol [[sup.13][C.sub.10]]retinyl acetate in oil as a reference dose with a breakfast containing 13 g fat. One week later, each subject consumed 7.9 [micro]mol trans [beta]-carotene in spirulina with a breakfast containing 22 g fat. All subjects followed diets low in carotenoid and vitamin A. Forty blood samples were collected from each subject over a span of 56 d. Concentrations and enrichments of retinol and [beta]-carotene in serum samples were determined by using HPLC and a mass spectrometer. Results: Compared with the serum response to [[sup.13][C.sub.10]]retinyl acetate dose, the mean conversion factor of spirulina [beta]-carotene to retinol was 4.5 [+ or -] 1.6 (range: 2.3-6.9) by weight. It was estimated that 80% of the conversion occurred within the first 24 h after spirulina administration. Conclusion: In a group of well-nourished, normal-weight Chinese men following low-vitamin A diets, 4.5 mg spirulina [beta]-carotene consumed with 22 g fat has the same vitamin A activity as does 1 mg retinyl acetate.