中文摘要：

目的 在前期对部分中老年农村居民进行了β-胡萝卜素（β-C）转化维生素A（VA）效率评价的基础上，再对10名农村中青年志愿者β-C转化效率进行研究。方法使用稳定同位素稀释法对10名38，49岁健康志愿者（男5，女5）进行β-C人体代谢实验。2周适应期和56天实验期内，志愿者接受常规膳食，避免大量VA和β-C摄入以及烟、酒和营养制剂。实验第1天，给受试者含6mg氘标记β-C（^2H8β-C）玉米油胶丸，随半流质早餐（脂肪热能比25％）一起摄入。实验第4天，受试者以同样方法摄入合3mg氘标记醋酸视黄醇（。HRRAc）油剂胶丸。实验第1天和第4天摄入标记物后0、3、5、7、9、11、13h时，第2、3、5、6、7、8、9、10、14、21、28、35、42、49和56天晨空腹时，采静脉血。用高效液相色谱仪（HPLC）测定血清类胡萝卜素成分浓度，使用气相质谱仪（GC／MS）测定血清中不同来源视黄醇的同位素丰度。根据VA浓度和同位素丰度，描述标记VA在体内应答的血液动力学曲线。结果 10名受试者口服^2H8β-C和^2H8RAc后，血清中^2H4视黄醇和^2H8视黄醇的应答反应均非常明显；52天时血清中^2H4视黄醇（来自^2H8β-C）的曲线下面积（AUC）平均为（1289±547）nmol／d；52天的^2H8视黄醇（来自^2H8RAc）的AUC平均为（3560±1058）nmol／d；以摄入的^2H^8RAc作为VA参照，计算来自口服^2H8β-C的^2H4视黄醇平均为（3434±1449）nmol／d。β-C转化为VA的转化系数平均为（3．89±2．76）：1（摩尔单位）[范围是（2．00～9．61）：1]或者（7．30±5．18）：1（质量单位）[范围是（3．76～18．05）：1]。结论 采用稳定同位素稀释技术，定量测定了10名中国农村中青年志愿者体内β-C转化为VA的效率。按质量单位计其转化比值平均为7．30：1。

英文摘要：

Objective As an extended study of β-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 β-C （11,011 （nmole or 6mg） 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 β-C dose, each volunteer took a reference dose of ^2H8 retinyl acetate （8,915 nmole or 3mg） 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 carutenoids 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 chemicalionization （GC-MS）. Results The average 52-day area under the serum 2H4 retinol response curve （from the ^2H8 β-C dose） was （1289 4-547） nmol/d and the 52-day area under the serum 2Hs 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 ^2H8β-C （11,011 nmol） was calculated to be equivalent to （3434 ± 1449） nmol of retinol. The calculated conversion factor of β-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