Vitamin A equivalence of spirulina β-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 β-carotene in humans. DESIGN: Spirulina was grown in a 23 atom% ²H₂O cultural solution. Spirulina β-carotene showed the greatest enrichment as [²H₁₀]trans β-carotene. Ten healthy Chinese men with a mean (±SD) serum retinol concentration of 1.7 ± 0.3 μmol/L and a body mass index (in kg/m²) of 23 ± 3 consumed 5.8 μmol [¹³C₁₀]retinyl acetate in oil as a reference dose with a breakfast containing 13 g fat. One week later, each subject consumed 7.9 μmol trans β-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 β-carotene in serum samples were determined by using HPLC and a mass spectrometer. RESULTS: Compared with the serum response to [¹³C₁₀]retinyl acetate dose, the mean conversion factor of spirulina β-carotene to retinol was 4.5 ± 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 β-carotene consumed with 22 g fat has the same vitamin A activity as does 1 mg retinyl acetate.