Folates dietary sources

Vitamins and minerals, whose main dietary sources are other than fruits and vegetables, are also likely to play a significant role in the prevention and repair of DNA damage, and thus are important to the maintenance of long-term health. Vitamin B12 is found in animal products, and deficiencies of B12 cause a functional folate deficiency, accumulation of the amino acid homocysteine (a risk factor for heart disease),46 and chromosome breaks. B12 supplementation above the RDA was necessary to minimize chromosome breakage.47 Strict vegetarians are at increased risk for developing vitamin B12 deficiency. 

Cyanocobalamine is a component of several coenzymes and has an effect on nucleic acid formation through its action in cycling 5-methyl-tetrahydrofolate back into the folate pool. The most important dietary sources of the vitamin are animal products. Vitamin Bl2 is also produced by many microorganisms. It is not surprising that vitamin B12 deficiency of dietary origin only occurs in vegetarians. 

Epidemiological studies suggest that suboptimal folate status is associated with an increased risk of colorectal and other cancers. It is difficult to determine the importance of folate per se, because the dietary sources of folate (mainly greenleafy vegetables) are also sources of avariety of other compounds... 

Folate deficiency may be epiphenomenal, because the major dietary sources of folate are the same as those of ascorbate. However, some patients with clear megaloblastic anemia respond to the administration of vitamin C alone, suggesting that there may be a role of ascorbate in the maintenance of... 

Folate is absorbed from dietary sources, such as those fisted above, mainly as reduced methyl- and formyl-tetrahy-dropteroylpolyglutamates. The bioavailabifity of folate from food sources is variable and dependent upon factors such as incomplete release firom plant cellular structure, entrapment in food matrix during digestion, inhibition of deglutamation by other dietary constituents, and possibly the degree of... 

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. 

Tree nuts can be good dietary sources (>10% of recommended dietary allowances [RDA] or adequate intake [Al]) of most vitamins except vitamins A and cobalamin (B,2). At suggested consumption level (1.5 ounces or 42.5g/day), acorn and pine nuts are excellent sources of folate and vitamin K (Table 2.7). In case of thiamin (Bj), niacin (B3), and pyridoxine (Bg), tree nuts offer alternative sources of these vitamins when more abundant animal sources are not available or are not consumed. 

In vitamin B12 deficiency, methionine synthase is inhibited causing increased levels of homocysteine and SAH. SAH in turn inhibits SAM mediated methylation, thereby leading to toxic levels of homocysteine causing direct damage to the vascular endothelium and inhibition of iV-methyl-o-aspartate receptors (NMDA) (Moretti et al. 2008). Homocysteine is produced entirely from the methylation cycle, as it is totally absent from any dietary source (Pietrzik and Bronstrup 1997). Hence, an elevated plasma homocysteine concentration is a sensitive marker for vitamin B12 and folate deficiency (Pametti et al. 1997). In addition, it can be due to increased frequency of impaired genetic capacity to metabolize homocysteine (Nilsson et al. 1996). 

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. 

The amount of foHc acid required for daily iatake is estimated based oa the minimum amouat required to maintain a certaia level of semm folate. The recommeaded dietary allowance (RDA) for foHc acid accounts for daily losses and makes allowances for variation ia iadividual aeeds and bioavailabiUty from food sources (85). The U.S. recommended daily allowance for adults is 400 p.g and for pregnant women is 800 ]1 (Table 4). 

The many diverse components of milk have demonstrable effects on human health. Perhaps, the most commonly associated component of dairy food is that of dietary calcium. Dairy products provide the most significant contribution to dietary calcium intake in the modem Western diet. It has been estimated that dairy products contribute to >72% of dietary calcium in the United States (Huth et al., 2006). Calcium is an important mineral for maintenance of optimal bone health (Bonjour et al., 2009) and is an integral component of key metabolic pathways relating to, for example, muscle contraction both in skeletal and smooth muscle (Cheng and Lederer, 2008). Further, dairy products contribute other essential nutrients in the diet, such as proteins, phosphorus, potassium, zinc, magnesium, selenium, folate, riboflavin, vitamin B12, and vitamin A (Haug et al., 2007 Huth et al., 2006). Low-fat milk alternatives are fortified with vitamin A and vitamin D which is added to milk and fermented milk in many countries making it an important source for vitamin D (Huth et al., 2006). 

Folale deficiency occurs in pregnancy on a wide scale. The increased utilization of the vitamin by die fetus and related tissues, as well as the secretion in milk during lactation, can place an increased demand on the dietary folates consumed by the mother. Sea ere folate deficiency leads to megaloblastic anemia. This disease, in which the synthesis of red blood cells is impaired, tends to occur with pregnancy in underdeveloped countries, but usually not in North America or Europe, Goat s milk is a poor source of folate and vitamin Bjj. Ovcrrchancc on goal s milk as a source of food for infants can result in a deficiency in these vitamins and in anemia. 

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