To the Editor The editorial by Mitchell1 welcomed the US Preventive Services Task Force recommendation that women of child-bearing age in the United States should take a daily supplement containing 400 to 800 μg of folic acid to prevent neural tube defects. But the rationale for the recommendation is puzzling. The recommendation makes sense for countries without mandatory folic acid fortification. However, as Mitchell says, 2 case-control studies in the United States after fortification have failed to show an additional benefit of folic acid supplementation in the prevention of neural tube defects. Mitchell suggests that folic acid fortification may be preventing nearly all cases of folic acid–related neural tube defects. Her suggestion is consistent with a “floor-effect” for folate-sensitive neural tube defects.2
Refsum H, Smith AD. Folic Acid for the Prevention of Neural Tube Defects. JAMA Pediatr. 2017;171(7):710–711. doi:10.1001/jamapediatrics.2017.0866
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