Hiraoka Mami
Department of Medical Chemistry, Kagawa Nutrition University, Sakado-shi, Saitama, Japan.
J Nutr Sci Vitaminol (Tokyo). 2004 Aug;50(4):238-45. doi: 10.3177/jnsv.50.238.
Various factors influence folate status and requirements. To investigate the folate status in young Japanese women (n=340, 20-22 y), I determined the serum folate and total homocysteine (tHcy), and examined the influence of methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism on folate status in a subgroup of 252 of the women. I calculated folate consumption based on records of food intake weighed over 3 d using the standard Tables of Food Composition in Japan (5th revised edition) and the US Food Composition Table based on the USDA nutrient database excluding fortification. Serum folate and total homocysteine (tHcy) levels were determined by chemiluminescent-competitive protein binding assay and HPLC, respectively. The mean intake of folate was 323+/-133 and 196+/-71 microg/d, and 86.5% and 42.1% of the participants consumed more than the RDA of 200 microg of folate, according to the Japanese and US tables, respectively. The main sources of dietary folate were vegetables, green tea and bread. Serum folate levels were significantly correlated with folate intake (r=0.249, p<0.001). Serum tHcy levels were above 15 micromol/L in four participants. I found significant negative correlations between serum tHcy and folate intake (r=-0.175, p<0.05), and between serum tHcy and serum folate (r=-0.297, p<0.0001). The frequencies of the CC, CT and TT genotypes of the MTHFR gene were 32.9, 51.6 and 15.5%, respectively. Among individuals with the TT genotype, serum folate and tHcy levels were lower and higher, respectively, than in those with the other genotypes, regardless of folate intake above RDA. These data suggest that the current RDA of folate estimated based on foreign data might not be sufficient for Japanese and that this value might require reassessment.
多种因素会影响叶酸状态和需求量。为调查日本年轻女性（n = 340，年龄20 - 22岁）的叶酸状态，我测定了她们的血清叶酸和总同型半胱氨酸（tHcy），并在252名女性组成的亚组中研究了亚甲基四氢叶酸还原酶（MTHFR）C677T基因多态性对叶酸状态的影响。我根据使用日本《食品成分标准表》（第5版修订版）和基于美国农业部营养数据库（不包括强化成分）的美国食品成分表对3天食物摄入量记录计算叶酸摄入量。血清叶酸和总同型半胱氨酸（tHcy）水平分别通过化学发光竞争蛋白结合法和高效液相色谱法测定。根据日本和美国的表格，叶酸的平均摄入量分别为323±133和196±71微克/天，分别有86.5%和42.1%的参与者摄入超过200微克叶酸的推荐膳食摄入量（RDA）。膳食叶酸的主要来源是蔬菜、绿茶和面包。血清叶酸水平与叶酸摄入量显著相关（r = 0.249，p < 0.001）。4名参与者的血清tHcy水平高于15微摩尔/升。我发现血清tHcy与叶酸摄入量之间存在显著负相关（r = -0.175，p < 0.05），血清tHcy与血清叶酸之间也存在显著负相关（r = -0.297，p < 0.0001）。MTHFR基因的CC、CT和TT基因型频率分别为32.9%、51.6%和15.5%。在TT基因型个体中，无论叶酸摄入量是否高于RDA，其血清叶酸水平较低，而血清tHcy水平较高。这些数据表明，基于国外数据估算的当前叶酸RDA可能对日本人来说并不足够，并可能需要重新评估该数值。
