Folic acid acts as a coenzyme (with vitamin B-12 and vitamin C) in the breakdown (metabolism) of proteins and in the synthesis of new proteins. It is necessary for the production of red blood cells and the synthesis of DNA (which controls heredity), as well as tissue growth and cell function. It also increases the appetite and stimulates the formation of digestive acids.

Synthetic folic acid supplements may be used in the treatment of disorders associated with folic acid deficiency, and may also be part of the recommended treatment for certain menstrual problems and leg ulcers.

• beans and legumes
• citrus fruits and juices
• wheat bran and other whole grains
• dark green leafy vegetables
• poultry, pork, shellfish
• liver

Folic acid deficiency may cause poor growth, graying hair, inflammation of the tongue (glossitis), mouth ulcers, peptic ulcer, and diarrhea. It may also result in hemolytic and megaloblastic anemias.

Toxicity from excessive folic acid intake does not normally occur, as folic acid is water soluble and regularly excreted by the body.

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.

Pregnant women often require additional supplementation as prescribed by the health care provider. Adequate folic acid is important to women in their childbearing years because it has been shown to prevent some kinds of birth defects, including neural tube defects. Women in this age group should make an effort to consume foods that are good sources of folic acid. Recent studies published by the Centers for Disease Control (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.

Specific recommendations for each vitamin depend on age, gender, and other factors (such as pregnancy).  The U.S. Department of Agriculture has a PDF file that lists these http://www.nal.usda.gov/fnic/dga/rda.pdfrecommendations.