Folic acid dietary sources

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In the early 1940s. R. J. Williams et al. used the term folic add in referring to a vitamin occurring in leaves and foliage of spinach, from the Latin for leaf (folium). Prc i-ously. it was called vitamin M and vitomin Bt/. Since then, folic acid has been found in whey, mushrooms, liver, yciut. bone marrow, soybeans, and fish meal, oil of which are ex-ccllent dietary sources. The structure (.sec diagram) has been proved by synthesis in many laboratories (e.g.. see Waller et al. -"-... 

Choiine. Choline is a component of many biomem-hranes and plasma phospholipids. Dietary sources include eggs. fish, liver, milk, and vegetables. These sources provide choline primarily as the phospholipid lecithin. Lecithin is hydrolyzed to glycerophosphorylcholinc by the intestinal mucosa before absorption. The liver liberates choline. Choline can be biosynthesized by humans con.sequcntly. it cannot be con.sidcred a (rue vitamin. Biosynthesis involves methylation of cthanolamine. The methyl groups arc provided by methionine or by a reaction involving vitamin B12 and folic acid. Therefore, deficiencies can occur only if all methyl donors are excluded from the diet. 

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Routes of exposure are oral, intravenous, intramuscular, and subcutaneous. Dietary sources of folic acid are green leafy vegetables, some fruits, legumes, eggs, yeast, whole grain cereals, lean beef, veal, liver, and kidneys. Heat destroys folic acid in cooked foods. 

Tetrahydrofolate (THF) The active form of the vitamin folic acid. THF is one of the major carriers of one-carbon units at various oxidation states for biosynthetic reactions. It is required for the synthesis of the nucleotide thymidylate (dTMP). Although bacteria can synthesize folic acid, eukaryotes must obtain folate from the diet. Dietary sources of folate include leafy green vegetables (e.g., spinach and turnip greens), citrus fruits, and legumes. Many breakfast cereals, breads, and other grain products are fortified with folate. 

FIG. 5. Isotopic enrichment of urinary folate in an adult female subject during chronic ingestion of a low-folate diet supplemented with d2-folic acid. The value of 0.284 enrichment represents the labeling (i.e., isotopic enrichment) of ingested folate from dietary and supplemental sources. In this figure, the data were fit to the two-pool, one-output model depicted in Fig. 3, which yielded the solid regression line (Gregory el aL, 1994). 

Increased absorption is almost certainly the cause of the raising of the blood and tissue levels of vitamin B12 by sorbitol and some other substances. Intestinal synthesis is responsible for the far more dramatic sparing of other B vitamins by sorbitol, ascorbic acid, and several other substances, so that animals become completely independent of dietary sources of these vitamins. Finally, the ability of ascorbic acid to prolong the life of animals deficient in folic acid is very probably due to the promotion of the synthesis of this vitamin in the tissues. 

Chemicals that inhibit the growth of microbes are known as antimetabolites. It turns out that certain amine-containing molecules known as sulfanilamides (which we will discuss in more detail shortly) are antimetabolites for those bacteria that rely on p-aminobenzoic acid. The reason the homology of their overall shapes, key features of which are highlighted above. Indeed, the enzymes that these bacteria use to synthesize folic acid cannot distinguish between these two molecules. And, when a sulfanilamide is used as a substrate instead of p-aminobenzoic acid, folic acid does not result. This event ultimately leads to bacterial death since enough of that essential nutrient is not synthesized. Such treatments turn out to be especially useful for humans because we derive our folic acid from dietary sources (folic acid is a vitamin). Thus, we do not have any enzymes that synthesize it from p-aminobenzoic acid and are, as a result, unaffected in any negative ways by a sulfanilamide therapy. 

Dietary folate intake determines folate nutritional status. It is therefore important to accurately measure folate in food using the best analytical platform currently available. In particular, folate analysis is confounded by several factors, such as the presence of many vitamers, low concentrations, physicochemical instability, and complex sample preparation [12]. It has been reported that the levels of endogenous 5-methyltetrahydrofolate and 5-formyltetrahydrofolate in canned chickpeas, a rich folate source, were 52 and 8 pg/lOO g, respectively [13]. Folate-fortified foods contain higher total folate concentrations than those found in natural folate-rich foods. We recently determined folic acid in Australian fortified bread varieties that was approximately 100 [tg/100 g [14]. 

There are two major sources of folate for humans folate that is naturally available in the diet and synthesized folate, which is typically supplied by bacteria in the large intestine. Folic acid is not a natural physiological form and is not commonly available in nature. Dietary folate compounds in the form of... 

Folic acid (pteroylglutamic acid) and related compounds are present at high concentration in liver, but spinach, broccoli, peanuts, and fresh fruit are also good dietary sources. The RDA is 300 pg. Folates are important for the synthesis of tetrahydrofolate which is important with cobalamin for a series of 1-carbon transfer reactions leading to DNA synthesis, failure of which leads to megaloblastic anemia. 

Folic acid deficiency, when it occurs, results more commonly from a failure of utilization than from an inadequate dietary intake. It is manifested by macrocytic anaemia and leucopenia. As the name suggests, green leaves are good sources so is yeast. 

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