MRC Vitamin Study

About the Trial

The Medical Research Council Vitamin Study randomized women in several countries who had previously had a pregnancy affected by a neural tube defect, such as spina bifida or anencephaly, to folic acid, other vitamins, both, or neither around conception. Folic acid reduced recurrence by 72 percent, while the other vitamins had no significant effect, and the trial was stopped early. Published in the Lancet in 1991, the result led public health bodies to recommend folic acid supplementation for women who could become pregnant, and to mandatory folic acid fortification of grain products in the United States in 1998 and in many other countries, preventing thousands of birth defects every year.