Rayburn W F, Stanley J R, Garrett M E
Department of Obsterics and Gynecology, University of Oklahoma College of Medicine, Oklahoma City, USA.
J Am Coll Nutr. 1996 Apr;15(2):121-5. doi: 10.1080/07315724.1996.10718576.
Approximately 50% of neural tube defects may be folate-preventable and perhaps even more in other countries where prevalence is high. The Public Health Service has issued the recommendation that all women of childbearing age in the United States who are capable of becoming pregnant should consume 400 micrograms of folic acid/day for the purpose of reducing this risk. Ways in which a reproductive age woman could achieve this goal include: 1) fortifying a food sample with folic acid, 2) consuming supplements containing at least 400 mcg of folic acid, or 3) increasing nutrient intake by eating foods rich in folate. Advantages of consuming foods high in folate content are that it is a natural behavior and consistent with other dietary recommendations. However, this method is dependent upon a proper diet, and equivalencies of conjugated (dietary form) vs. unconjugated (in supplements) folate are unknown. The benefit of a supplementation policy is that the appropriate group can be targeted as pregnancies are planned, whereas primary limitations to taking a supplement would be compliance and most cases in need would not be reached. The advantage of fortification is that it is likely to reach everyone before conception, while the major disadvantage is that nontargeted populations will also receive more folic acid. Adequate consumption of folic acid should begin before and continue during at least the first 4 weeks after conception when the fetal neural tube is being formed. Standard methods of screening for neural tube defects should continue during pregnancy. The risk of a recurrent neural tube defect is 2-3%, and a higher periconception daily intake of folic acid (4 mg per day) is recommended.
大约50%的神经管缺陷可以通过叶酸预防，在患病率较高的其他国家，这一比例可能更高。美国公共卫生服务部门已发布建议，美国所有有怀孕能力的育龄妇女应每天摄入400微克叶酸，以降低这种风险。育龄妇女实现这一目标的方法包括：1）用叶酸强化食物样本；2）服用含有至少400微克叶酸的补充剂；或3）通过食用富含叶酸的食物增加营养素摄入量。食用富含叶酸的食物的优点是这是一种自然行为，并且符合其他饮食建议。然而，这种方法取决于合理饮食，且共轭（饮食形式）与非共轭（补充剂形式）叶酸的等效性尚不清楚。补充剂政策的好处是可以在计划怀孕时针对合适的人群，而服用补充剂的主要限制是依从性问题，并且无法覆盖大多数有需求的情况。强化的优点是在受孕前可能惠及所有人，而主要缺点是未针对的人群也会摄入更多叶酸。叶酸的充分摄入应在受孕前开始，并在受孕后至少前4周持续进行，此时胎儿神经管正在形成。孕期应继续采用神经管缺陷的标准筛查方法。神经管缺陷复发的风险为2%-3%，建议在受孕前后每天摄入更高剂量的叶酸（每天4毫克）。
