title: beta-Carotene-vitamin A equivalence in Chinese adults assessed by an isotope dilution technique.
abstract: The present study was carried out to determine the conversion factor of synthetic (2)H-labelled beta-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 [(2)H8]beta-carotene (6 mg) in oil on the first day of the experiment, and a reference dose of [(2)H8]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. beta-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 beta-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 beta-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.
authors.affiliation: Institute of Medical Nutrition, Qingdao University Medical College, Qingdao, China 266021. zxwong@public.qd.sd.cn
authors.forename: Zhixu
authors.initials: Z
authors.lastname: Wang
authors.forename: Shian
authors.initials: S
authors.lastname: Yin
authors.forename: Xianfeng
authors.initials: X
authors.lastname: Zhao
authors.forename: Robert M
authors.initials: RM
authors.lastname: Russell
authors.forename: Guangwen
authors.initials: G
authors.lastname: Tang
mesh_terms: D000042:Absorption; D000975:Antioxidants / Q000378:metabolism*; D019540:Area Under Curve; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003903:Deuterium; D005260:Female; D006801:Humans; D007201:Indicator Dilution Techniques; D008099:Liver / Q000378:metabolism; D008297:Male; D013058:Mass Spectrometry / Q000379:methods; D008875:Middle Aged; D014801:Vitamin A / Q000097:blood / Q000378:metabolism*; D019207:beta Carotene / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics
chemical_list: D000975:Antioxidants; D019207:beta Carotene; D014801:Vitamin A; D003903:Deuterium