Objective: As an extended study of beta-Carotene-vitamin A equivalence in Chinese adults, we carried out an experiment on 10 (5 males and 5 females) rural volunteers aged 38 - 49 years, which would be complementary to the early reported study on subjects aged 50 - 60 years.
Methods: Ten healthy Chinese adult volunteers aged 38-49 years were recruited in a 56 days experiment, which included residency in the Metabolic Research Unit (first 10 days and in home (last 46 days). A physiological dose of 2H8 beta-C (11,011 (nmole or 6 mg) in oil was given with a liquid diet (25% energy from fat) to the volunteers in the first day of the experiment. Three days after the 2H8 beta-C, each volunteer took a reference dose of 2H8 retinyl acetate (8,915 nmole or 3 mg) in oil with the same liquid diet. Serum samples were collected at 0, 3, 5, 7, 9, 11 and 13 hours of the first and the fourth days of study, and fasting serum samples were also collected daily in first 10 days and then weekly at morning of 14th, 21st, 28th, 35th, 42nd, 49th and 56th day after a 12-hours overnight fast. Serum retinol and carotenoids concentrations were measured by high performance liquid chromatography (HPLC). Also retinol fraction was extracted from serum and isolated by HPLC. The serum retinal enrichments were determined by using gas chromatograph/mass spectrometry with electron capture negative chemical ionization (GC-MS).
Results: The average 52-day area under the serum 2H4 retinol response curve (from the 2H8 beta-C dose) was (1289 +/- 547) nmol/d and the 52-day area under the serum 2H8 retinol response curve (from the 2H8 retinyl acetate dose) was (3560 +/- 1058) nmol/d. By using 2H8 retinyl acetate as the vitamin A reference, the 2H4 retinol formed from 2H8 beta-C (11,011 nmol) was calculated to be equivalent to (3434 +/- 1449) nmol of retinol. The calculated conversion factor of beta-C to retinol ranged from 2.00 - 9.61 to 1 with an average of (3.89 +/- 2.76) to 1 on a molar basis, or 3.76 - 18.05 to 1 with an average of (7.30 +/- 5.18) to 1 on a weight basis.
Conclusion: The conversion of beta-C to vitamin A in 10 middle-aged Chinese adults had been quantitatively determined by using a stable isotope reference method, and an average conversion ratio of 7.30 : 1 to 1 on a weight basis was found in this study.