Folic acid.(Drugs, Pregnancy And Lactation)

It has now been more than a decade since the publication of two critical studies that resulted in the firm conclusion that folic acid supplementation in early pregnancy prevents neural tube defects.

These findings led to the recommendation that women of childbearing age should take a daily folic acid supplement, as well as Canadian and U.S. laws stipulating that flour must be fortified with folic acid. But there is still plenty of room for improvement: Even today, many women do not take supplements, and food fortification is not an insurance policy for preventing neural tube defects in all cases.

Current recommendations suggest that women who are capable of bearing children should consume at least 400 [micro]g of folic acid daily, and those planning a pregnancy should take a prenatal vitamin with at least that amount, continuing through the first trimester. Women who have had a child with a neural tube defect, and women on certain drugs that can cause neural tube defects, like valproate or carbamazepine, should take 4 mg of folic acid daily

Most prenatal vitamins today have 800-900 [micro]g of folic acid, but many women don't know they're pregnant until well into the first trimester. This is too late to start supplementation, because the neural tube is closed by 4 weeks' gestation.

The United States and Canada therefore passed regulations to fortify flour with folic acid. Studies have indicated that this fortification has resulted in the doubling of folic acid levels in the Canadian and U.S. population at large; in Canada, it has resulted in drops in neural tube defect rates. There are now studies from Nova Scotia, Ontario, and the United States showing a very clear decrease in neural tube defects that is directly related to fortification.

Still, many women do not consume sufficient amounts of bread or other products containing flour. In a Motherisk study, we measured folic acid levels in a large Canadian population and found that a significant proportion still have serum folic acid levels below 900 nanomoles per liter, which was the level associated with prevention of neural tube defects, according to an Irish study

Over the past decade, the 400-[micro]g daily dose has been the gospel, but a recent reanalysis of published studies led by Dr. Nicholas Wald of London concluded that this dose is not enough to reach the serum level of 900 nanomoles, and that 1 mg daily--possible even more--is necessary to reach this level (Lancet ...