Authors’ reply to Smith and colleaguesBMJ 2016; 352 doi: https://doi.org/10.1136/bmj.i746 (Published 16 February 2016) Cite this as: BMJ 2016;352:i746
- James L Mills, senior biomedical research service scientist1,
- Aggeliki Dimopoulos, IRTA postdoctoral fellow1
- 1Epidemiology Branch, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA
Some of Smith and colleagues’ statements about our editorial require clarification.1 2 They interpret our statement that: “No important adverse effects have been identified to date, probably because a modest level of fortification has proved very effective in preventing these devastating birth defects” as a claim that fortification is safe because it is effective for one condition. This interpretation is incorrect. Food fortification in the US has resulted in an average exposure to about 200 µg of folic acid per day.3 This is half the recommended dietary allowance (RDA). We were indicating that it is not surprising that no adverse effects have been seen from such a modest dose. As Smith and colleagues point out, WHO states that even high folic acid exposure, in contrast to the small amount fortification delivers, “has not reliably been shown to be associated with negative effects.”4 Thus, the postulated adverse effects, if any, have not been proved.
The reduction in neural tube defect rates produced by fortification is proportional to the underlying rate,5 and reported reductions vary depending on the completeness of ascertainment.6 Many …