The name of the B-vitamin folate comes from the Latin word folium, meaning “leaf”. It was given this name because leafy green vegetables are excellent sources. Folate is the generic name, referring to the various forms of the vitamin found naturally in foods. The term folic acid refers to the synthetic form of the vitamin found in supplements and fortified foods.
FOLATE IN FOODS
The biological availability of folate in food from a mixed diet is generally thought to be about 50% if folic acid, but it may be loser to 80%.
Foods that have the largest amount and most bioavailable folate are liver, legumes, and leafy green vegetables. Other rich sources of folate include avocados and oranges. Bread and cereal products from milled grains are fortified with folic acid, making them good sources as well.
Ready-to-eat cereals, bread, legumes, oranges and grapefruit juice, lettuce, milk, and potatoes are leading sources of this vitamin. Although milk and potatoes are not particularly rich sources of folate, they are so commonly consumed that their contribution to folate intake is relatively high.
FUNCTIONS OF FOLATE
Folate coenzymes are required for the symthesis and maintanance of new cells. Folate coenzymes function in metabolic pathways in which single carbon groups are exchanged.
The folate coenzymes are formed from a central coenzyme form called tetrahydrofolic acid (THFA). Folate coenzymes are critical for DNA synthesis, and amino acid metabolism.
FOLATE NEEDS AND DIETARY FOLATE EQUIVALENTS
The folate RDA for adults is 400 μg/day, as is the Daily Value on food and supplement labels. The RDA is expressed as dietary folate equivalents (DFEs). DFEs reflect the differences in the absorption on food folate and synthetic folic acid. The relationship between DFEs, food folate, and folic acid is as follows:
1 DFE = 1 μg food folate = 0.6 μg folic acid taken with food = 0.5 μg folic acid taken on an empty stomach
DFEs are calculated using this equation:
DFE = μg food folate + (μg folic acid x 1.7)
For example, the Daily Value for a serving of ready-to-eat breakfast cereal is listed on the label as 50%, so the amount of folic acid is 200 μg per serving (Daily Value of 400 μg x 0.50). Because this folate is mainly synthetic folic acid, the 200 μg is multiplied by 1.7, yielding 340 μg DFE. If the diet also contains 300 μg of food folate, the total DFE intake is 640 μg DFE, which exceeds the adult RDA.
UPPER LEVEL FOR FOLATE
The Upper Level for synthetic folic acid is set at 1000 μg (1 mg); intakes above this level may mask a vitamin B-12 deficiency. The Upper Level does not apply to folate foods because absorption is limited. In response to the concern that high doses of folic acid might mask vitamin B-12 deficiency, the FDA limits the amount of folic acid in non-prescription vitamin supplements.
These levels are set at 400 μg for non-pregnant individuals when no statement of age is listed on the supplement label. When age-related doses are listed, there can be no more than 100 μg for infants, 300 μg for children, and 400 μg for adults. Over-the-counter prenatal supplements can contain 800 μg.
FOLATE DEFICIENCY
Folate deficiency can result from low intake, inadequate absorption (often associatted with long term alcohol intake), increased needs (most commonly occuring during pregnancy), compromised utilization (typically associated with vitamin B-12 deficiency), the use of certain chemotherapy, medications and excessive excretion.
Persons at risk for developing a folate deficiency include chronic alcoholics, those with very poor diets, and those who take certain medications, including anti-convulsants. In addition, folate deficiencies (other than neural tube defects), sometimes occur in pregnant women because pregnancy greatly increases the need for folate (600 μg DFE/day).
Pregnant women require extra folate because of the increased rate of cell division, and thus of DNA synthesis, in their own bodies and in the developing fetus. Prenatal care often includes prenatal multivitamin and mineral supplements fortifies with folate to compensate for the extra needs associated with pregnancy.
