Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them can also be used to assess the nutrient intakes of individuals.
Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy established when evidence is insufficient to develop an RDA.Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals often used to plan nutritionally adequate diets for individuals.These values, which vary by age and sex, include: DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. Intake recommendations for folate and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by an expert committee of the Food and Nutrition Board (FNB) at the National Academies of Sciences, Engineering, and Medicine. A homocysteine cutoff of 10 micromol/L has been proposed for assessing folate status in populations. The most commonly used cutoff value for elevated homocysteine levels is 16 micromol/L, although slightly lower values of 12 to 14 micromol/L have also been used. Homocysteine levels, however, are not a highly specific indicator of folate status because they can be influenced by other factors, including kidney dysfunction and deficiencies of vitamin B12 and other micronutrients. Plasma homocysteine concentration is a commonly used functional indicator of folate status because homocysteine levels rise when the body cannot convert homocysteine to methionine due to a 5-MTHF deficiency.
Ī combination of serum or erythrocyte folate concentration and indicators of metabolic function can also be used to assess folate status. Erythrocyte folate concentrations provide a longer-term measure of folate intakes a concentration above 140 ng/mL indicates adequate folate status. This indicator, however, is sensitive to recent dietary intake, so it might not reflect long-term status. Serum folate concentrations are commonly used to assess folate status a value above 3 ng/mL indicates adequacy. The total body content of folate is estimated to be 15 to 30 mg about half of this amount is stored in the liver and the remainder in blood and body tissues. Folate is also synthesized by colonic microbiota and can be absorbed across the colon, although the extent to which colonic folate contributes to folate status is unclear. Whether unmetabolized folic acid has any biological activity or can be used as a biomarker of folate status is not known. When the capacity of dihydrofolate reductase is exceeded, unmetabolized folic acid can be present in the blood. The activity of dihydrofolate reductase varies greatly among individuals. The main form of folate in plasma is 5-MTHF. Before entering the bloodstream, the enzyme dihydrofolate reductase reduces the monoglutamate form to THF and converts it to either methyl or formyl forms. Passive diffusion also occurs when pharmacological doses of folic acid are consumed. When consumed, food folates are hydrolyzed to the monoglutamate form in the gut prior to absorption by active transport across the intestinal mucosa. An impairment of this reaction initiates a process that can lead to megaloblastic anemia, one of the hallmarks of folate deficiency. Another folate-dependent reaction, the methylation of deoxyuridylate to thymidylate in the formation of DNA, is required for proper cell division. One of the most important folate-dependent reactions is the conversion of homocysteine to methionine in the synthesis of S-adenosyl-methionine, an important methyl donor. Some dietary supplements also contain folate in the monoglutamyl form, 5-MTHF (also known as L-5-MTHF, 5-methyl-folate, L-methylfolate, and methylfolate).įolate functions as a coenzyme or cosubstrate in single-carbon transfers in the synthesis of nucleic acids (DNA and RNA) and metabolism of amino acids. Folic acid is the fully oxidized monoglutamate form of the vitamin that is used in fortified foods and most dietary supplements. Food folates are in the tetrahydrofolate (THF) form and usually have additional glutamate residues, making them polyglutamates. “Folate,” formerly known as “folacin” and sometimes “vitamin B9,” is the generic term for naturally occurring food folates, and folates in dietary supplements and fortified foods, including folic acid.
Introductionįolate is a water-soluble B vitamin that is naturally present in some foods, added to others, and available as a dietary supplement. For a reader-friendly overview of Folate, see our consumer fact sheet on Folate. This is a fact sheet intended for health professionals.
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