Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
Br J Nutr. 2010 Mar;103(5):724-9. doi: 10.1017/S0007114509992339. Epub 2009 Oct 26.
Folic acid (pteroylmonoglutamic acid) has historically been used as the reference folate in human intervention studies assessing the relative bioavailability of dietary folate. Recent studies using labelled folates indicated different plasma response kinetics to folic acid than to natural (food) folates, thus obviously precluding its use in single-dose experiments. Since differences in tissue distribution and site of biotransformation were hypothesised, the question is whether folic acid remains suitable as a reference folate for longer-term intervention studies, where the relative bioavailability of natural (food) folate is assessed based on changes in folate status. Healthy adults aged 18-65 years (n 163) completed a 16-week placebo-controlled intervention study in which the relative bioavailability of increased folate intake (453 nmol/d) from folate-rich foods was assessed by comparing changes in plasma and erythrocyte folate concentration with changes induced by an equal reference dose of supplemental (6S)-5-methyltetrahydrofolic acid or folic acid. The relative increase in plasma folate concentration in the food group was 31 % when compared with that induced by folic acid, but 39 % when compared with (6S)-5-methyltetrahydrofolic acid. The relative increase in erythrocyte folate concentration in the food group when compared with that induced by folic acid was 43 %, and 40 % when compared with (6S)-5-methyltetrahydrofolic acid. When recent published observations were additionally taken into account it was concluded that, in principle, folic acid should not be used as the reference folate when attempting to estimate relative natural (food) folate bioavailability in longer-term human intervention studies. Using (6S)-5-methyltetrahydrofolic acid as the reference folate would avoid future results' validity being questioned.
叶酸（蝶酰单谷氨酸）在历史上一直被用作评估膳食叶酸相对生物利用度的人体干预研究中的参考叶酸。最近使用标记叶酸的研究表明，叶酸与天然（食物）叶酸相比，其血浆反应动力学不同，因此显然不能在单剂量实验中使用。由于假设存在组织分布和生物转化部位的差异，问题是叶酸是否仍然适合作为长期干预研究的参考叶酸，在这些研究中，基于叶酸状态的变化来评估天然（食物）叶酸的相对生物利用度。18-65 岁的健康成年人（n 163）完成了一项为期 16 周的安慰剂对照干预研究，其中通过比较血浆和红细胞叶酸浓度的变化与补充（6S）-5-甲基四氢叶酸或叶酸引起的变化，评估增加叶酸摄入（453 nmol/d）来自富含叶酸的食物的相对生物利用度。与叶酸相比，食物组中血浆叶酸浓度的相对增加为 31%，但与（6S）-5-甲基四氢叶酸相比，增加了 39%。与叶酸相比，食物组中红细胞叶酸浓度的相对增加为 43%，与（6S）-5-甲基四氢叶酸相比，增加了 40%。当额外考虑到最近发表的观察结果时，得出的结论是，原则上，在尝试估计长期人体干预研究中天然（食物）叶酸相对生物利用度时，不应将叶酸用作参考叶酸。使用（6S）-5-甲基四氢叶酸作为参考叶酸将避免未来结果的有效性受到质疑。
