Folic acid is widely distributed in nature; only limited amounts of free folic acid occur in natural products, and most feed sources contain predominantly polyglutamyl folic acid. Soybeans, other beans, nuts, some animals, products, and citrus fruits are good sources. Folic acid is abundant in green leafy materials and organ meats. The abundance of folic acid in green forages is shown by the higher concentrations of folic acid in milk from grazing herds than from herds fed dry hay.

Folic Acid in Immune Response

Folacin is the generic descriptor not only for the original vitamin, folic acid, but also for related compounds that qualitatively show folic acid activity, the pure substance being designated pteroylmonoglutamic acid. Its chemical structure contains three distinct parts, consisting of
glutamic acid, a para-aminobenzoic acid residue, and a pteridine nucleus.

Folic acid, in the form 5,6,7,8-tetrahydrofolic acid, is indispensable in the transfer of singlecarbon units in various reactions, a role analogous to that of pantothenic acid in the transfer of twocarbon units. Folic acid requirements are related to the type and the level of production. Growth rate, age, and pregnancy influence folic acid requirements.

The requirement decreases with age because diminished growth rate reduces the need for DNA synthesis. Increased catabolism of folic acid is a feature of pregnancy. Studies with humans (McPartlin et al. 1993) demonstrated enhanced folic acid catabolism; this was a feature of pregnancy per se and not simply due to increased weight.

The role of folic acid in biochemical reactions, such as metabolism of amino acids and synthesis of DNA, renders it a critical nutrient in embryogenesis (Almeida and Cardoso 2011). Folic acid supplementation was primarily indicated for the prevention and treatment of megaloblastic and maternal anemia (Almeida and Cardoso 2011).

Supplementation is also indicated in individuals with a genetic defect requiring greater amounts of folate than that can be derived from the diet (AshfieldWatt et al. 2002). Recent findings on folic acid supply and effects during pregnancy, lactation, and infancy were presented (Hermoso et al. 2011).

Liu et al. (2011) studied and reported that supplementation of micronutrients might increase immune function and reduce the incidence of common infections in type 2 diabetic outpatients. Folic acid fortification of wheat has become widespread in the Americans, a strategy adopted by Canada and the United States and about 20 Latin American countries.

Susumu studied folate deficiency among aged patients and its amelioration through the consumption of folic acid–fortified rice and concluded the nutritional benefits of folic acid in geriatric patients