Folate is essential for women who want to prevent major pregnancy complications, health experts have said for years.

However, a new federal report shows that the nutrient's level has decreased dramatically among non-pregnant American women of childbearing age, causing some doctors to worry that the numbers of birth defects may start climbing.

Researchers for the U.S. Centers for Disease Control and Prevention said average levels of folate in the blood fell from 8 percent to 16 percent between 1999 and 2004, based on their exams of 4,500 women 15 to 44.

During the same period, dramatic declines in neural tube defects from the late 1990s may have leveled off by 2004, according to the agency's weekly Morbidity and Mortality Weekly Report.

To prevent such defects like spina bifida, the federal government began mandating in 1998 that cereal-grain products get fortified with folate, which is also known as folic acid. Federal health experts recommend that women of childbearing age consume at least 400 micrograms of folic acid daily through dietary supplements, fortified foods and folate-rich foods.

Possible causes 

Researchers blame the drop on:

•  Fewer women taking folate supplements. Vitamins and supplements are the best ways to get the recommended daily dose of 400 micrograms of folic acid, but only a third of women of child-bearing age take them, according to the CDC.

•  Fewer folate-fortified foods. Some fortified foods are avoided by women on low-carb diets. In addition, whole-grain breads, which have grown in popularity, were not in the government's mandate because they already contain some folate, but not as much as in fortified bread.

•  Fewer foods naturally rich in folate.

•  Variations in the amount of folate added to food.

•  Increase in complication risk factors, such as obesity, that are linked to lower folate levels.

An earlier CDC study showed that women who might become pregnant successfully raised their folate levels after the mandate took effect. But recent information culled from two national surveys established the decline.

One of the B vitamins, folate is needed for the production of red and white blood cells and platelets, DNA in cells, and growth.

Since your body only contains a small amount of folic acid, you must get the nutrient regularly from supplements and liver, yeast, bananas, oranges, spinach and other leafy vegetables, eggs, lima beans, milk and other foods.