Volume 91, Issue 1, January (2004), pp. 121-131 © The Author 2004
doi:10.1079/BJN20031030

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β-Carotene–vitamin A equivalence in Chinese adults assessed by an isotope dilution technique

Zhixu Wang^1,2, Shian Yin¹, Xianfeng Zhao¹, Robert M. Russell³, Guangwen Tang^3
1National Institute for Nutrition and Food Safety, Chinese Centre for Disease Control and Prevention, Room 202, 29 Nanwei Road, Xuanwu District, Beijing, China, 100050
²Institute of Medical Nutrition, Qingdao University Medical College, Qingdao, China, 266021
³Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, MA, USA, 02111

 (Received 28 January 2003–Revised 22 September 2003–Accepted 24 September 2003)

The present study was carried out to determine the conversion factor of synthetic ²H-labelled β-carotene to vitamin A in Chinese adults by using a stable-isotope dilution technique. Fifteen healthy volunteers aged 50–60 years were recruited for a 55 d experiment. The volunteers (nine males and six females) were each given a physiological dose of [²H₈]β-carotene (6 mg) in oil on the first day of the experiment, and a reference dose of [²H₈]retinyl acetate (3 mg) in oil was given on the fourth day. Serum samples were collected at 0, 3, 5, 7, 9, 11, and 13 h on the first and the fourth days of the study, daily for 10 d, and then weekly from days 14 to 56. β-Carotene and retinol were extracted from serum and isolated by HPLC, and their enrichments were respectively determined by using GC–electron capture negative chemical ionisation-MS and LC–atmospheric pressure chemical ionisation interface-MS. Four of the subjects exhibited β-carotene to vitamin A conversion factors of >29·0:1 on a molar basis and were termed ‘poor converters’. In the eleven normal converters (seven males and four females), the calculated conversion factors of β-carotene to retinol ranged from 2·0:1 to 12·2:1 with an average of 4·8 (sd 2·8):1 on a molar basis, and from 3·8:1 to 22·8:1 with an average of 9·1 (sd 5·3):1 on a weight basis. The 52 d post-intestinal absorption conversion was estimated to be about 30 % of the total converted retinol.

Keywords:
β-Carotene, Vitamin A, Biological conversion efficiency, Isotope dilution technique

Abbreviations:
APCI, atmospheric pressure chemical ionisation, AUC, area under the curve, ECNCI, electron capture negative chemical ionisation, HNRCA, Human Nutrition Research Center on Aging at Tufts University, RAc, retinyl acetate