Recommended daily allowances (RDAs) are defined as the levels of intake of essential nutrients that, on the basis of scientific knowledge, the Food and Nutrition Board judges to be adequate to meet the known nutrient needs of practically all healthy persons.

The best way to get the daily requirement of essential vitamins is to eat a balanced diet that contains a variety of foods from the food guide pyramid.

Most people in the United States have an adequate dietary intake of folic acid because it is plentiful in the food supply.

However, pregnant women often require additional supplementation as prescribed by a health care provider. Adequate folic acid is important for pregnant women because it has been shown to prevent some kinds of birth defects, including neural tube defects such as spina bifida. Many foods are now fortified with folic acid to help prevent these kinds of birth defects.

Women in their childbearing years should make an effort to consume foods that are good sources of folic acid. Studies published by the Centers for Disease Control and Prevention (CDC) suggest that women who receive supplements of folic acid BEFORE CONCEPTION may reduce the risk for neural tube defects by 50%. Women who plan to become pregnant may want to discuss taking a multivitamin with their health care provider if they are not already doing so.

Specific recommendations for each vitamin depend on age, gender, and other factors (such as pregnancy). The U.S. Department of Agriculture offers a PDF file that lists these recommendations.