Kalmbach Renee D, Choumenkovitch Silvina F, Troen Aron M, D'Agostino Ralph, Jacques Paul F, Selhub Jacob
Vitamin Metabolism and Aging Laboratory, Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111, USA.
Am J Clin Nutr. 2008 Sep;88(3):763-8. doi: 10.1093/ajcn/88.3.763.
The implementation of folic acid fortification in the United States has resulted in unprecedented amounts of this synthetic form of folate in the American diet. Folic acid in circulation may be a useful measure of physiologic exposure to synthetic folic acid, and there is a potential for elevated concentrations after fortification and the possibility of adverse effects.
We assessed the effect of folic acid fortification on circulating concentrations of folic acid and 5-methyltetrahydrofolate in the Framingham Offspring Cohort.
This is a cross-sectional study that used plasma samples from fasting subjects before and after fortification. Samples were measured for folate distribution with the use of an affinity-HPLC method with electrochemical detection.
Among nonsupplement users, the median concentration of folic acid in plasma increased from 0.25 to 0.50 nmol/L (P < 0.001) after fortification, and among supplement users the median increased from 0.54 to 0.68 nmol/L (P = 0.001). Among nonsupplement users, the prevalence of high circulating folic acid (>/=85th percentile) increased from 9.4% to 19.1% (P = 0.002) after fortification. Among supplement users, the prevalence of high circulating folic acid increased from 15.9% to 24.3% (P = 0.02). Folic acid intake and total plasma folate were positively and significantly related to high circulating folic acid after adjustment for potential confounding factors (P for trend < 0.001).
Folic acid fortification has resulted in increased exposure to circulating folic acid. The biochemical and physiologic consequences of this are unknown, but these findings highlight the need to understand the effects of chronic exposure to circulating folic acid.
美国实施叶酸强化措施后，美国人饮食中这种合成形式的叶酸含量达到了前所未有的水平。循环中的叶酸可能是衡量生理上接触合成叶酸的一个有用指标，强化后叶酸浓度有可能升高，且存在产生不良反应的可能性。
我们评估了叶酸强化对弗雷明汉后代队列中叶酸和5-甲基四氢叶酸循环浓度的影响。
这是一项横断面研究，使用了强化前后空腹受试者的血浆样本。采用亲和高效液相色谱法结合电化学检测对样本进行叶酸分布测定。
在未服用补充剂的人群中，强化后血浆中叶酸的中位数浓度从0.25纳摩尔/升增加到0.50纳摩尔/升（P<0.001）；在服用补充剂的人群中，中位数从0.54纳摩尔/升增加到0.68纳摩尔/升（P = 0.001）。在未服用补充剂的人群中，强化后循环叶酸水平高（≥第85百分位数）的患病率从9.4%增加到19.1%（P = 0.002）。在服用补充剂的人群中，循环叶酸水平高的患病率从15.9%增加到24.3%（P = 0.02）。在对潜在混杂因素进行调整后，叶酸摄入量和血浆总叶酸与循环叶酸水平高呈正相关且具有显著相关性（趋势P<0.001）。
叶酸强化导致循环叶酸的暴露增加。其生化和生理后果尚不清楚，但这些发现凸显了了解长期暴露于循环叶酸的影响的必要性。
