Not too little, not too much

Two vitamins have been making headlines in recent years because of their relation to congenital malformations: folic acid because it can prevent some, and vitamin A because it can cause them. In both cases the crucial issues are how much should be consumed in early pregnancy, and whether the vitamins should come from food, pills, or both.

There is now unimpeachable evidence that an adequate consumption of folic acid before conception and during the first two to three months of pregnancy significantly reduces the risk of neural tube defects.1 2 There is increasing evidence that folic acid may also reduce the risk of some other birth defects.3 The health departments of many countries have advised women who may become pregnant to increase their folic acid intake by 0.4 mg (400 μg) daily. This amount seems to be both safe and effective.

Unfortunately, although surveys show that the implementation of these policies is gradually increasing, only a minority of …