**4. Food containing folic acid**

Folic acid is not found in natural food sources; however, folate is the natural form of vitamin B9, which is water soluble and naturally found in many foods commonly in dark green and leafy vegetables such as spinach, asparagus, romaine lettuces, broccoli, bok choy, turnip green, beet, dried or fresh beans, and peas (**Table 2**). The main dietary sources of folate are spinach, white beans, asparagus, dark-green leafy vegetables, Brussels sprouts, soybean, orange, and melons [19]. In addition to the aforesaid, beef liver, black-eyed peas, asparagus, lettuce, avocado, broccoli, mustard greens, green peas, kidney beans, canned tomato juice, orange juice, dry-roasted peanuts, fresh orange and grapefruit, papaya, banana, hard-boiled egg, and cantaloupe are also good sources of folate. Other sources of this vitamin include sunflower seeds, avocados, peanuts, orange juice, pineapple juice, cantaloupe, honeydew melon, grapefruit juice, banana, raspberry, papaya, grapefruit, strawberry, corn, and wheat germ. Among animal products, liver (the folate storage organ in mammals) and liver products, whole eggs, and baker's yeast are rich in folates. The major staple crops of the globe *viz*., rice and maize are low in folates (**Table 3**) [20]. However, pulses and other legumes and green


#### **Table 2.** *Folate content in raw vegetables.*

#### *B-Complex Vitamins - Sources, Intakes and Novel Applications*


#### **Table 3.**

*Folate content in raw cereal grains and legume seeds.*


*Vitamin B9 in Dark Green Vegetables: Deficiency Disorders, Bio-Availability, and Fortification… DOI: http://dx.doi.org/10.5772/intechopen.100318*


#### **Table 4.**

*Folate content in cooked food.*

leafy vegetables such as spinach, asparagus, lettuce, and Brussels sprouts are rich in folates (**Tables 2** and **3**). It has been reported that folate concentration in rice cultivars ranged from 11.0 to 51 μg/100 g with a mean of 26.0 μg/100 g [20, 21]. Singh [22] have also reported that legumes are a rich source of folates, followed by green vegetables, spices, and cereals. According to USDA [23], the amount of folates varies from 0.1 to 0.5 μg/g in brown rice, which is reduced by 60–67% during milling of rice. The folate content deteriorates on long storage (23%) and also during boiling (48.3%). Folate intake is strongly influenced by various methods of cooking that can degrade the natural forms of the vitamin in foods (**Table 4**). Steaming of spinach or broccoli, in contrast, resulted in no significant decrease in folate content, even for the maximum steaming periods of 4.5 min (spinach) and 15.0 min (broccoli).

#### **5. Folate bioavailability**

Folates from natural food sources can enhance the folate status only to a limited extent because of their poor stability while being cooked and also less bioavailability when compared with the synthetic vitamin and folic acid [24]. In addition to the less bioavailability of food folates, the poor stability of folates in foods (particularly green vegetables) while cooking can substantially reduce the amount of vitamin, which is ingested, and this may be an additional factor that limits the ability of food folates from naturally available cooked foods to enhance the folate status. Folate bioavailability from different foods is considered to be dependent on several factors, including the food matrix, the intestinal deconjugation of polyglutamyl folates, the instability of certain labile folates during digestion, and the presence of certain dietary constituents that may enhance folate stability during digestion. However, limited folate bioavailability data are available for vegetables, fruits, cereal products, and fortified foods; hence, it is difficult to evaluate the bioavailability of food folate or whether intervention with food folate improves folate status. The amount of folate that is absorbed and utilized physiologically varies among different food sources and different chemical forms of the vitamin. At least 85% of folic acid is

estimated to be bioavailable when taken with food [12, 25], whereas the bioavailability of food folate is commonly estimated at about 50% of folic acid bioavailability [26], but this should be considered as a rough estimate, as data on bioavailability of food folate vary between 30 [24] and 98% [27]. The chemically most stable folate form is synthetic folic acid [28], which is cheap to produce and therefore used for dietary supplements and food fortification. The folic acid consumed as a supplement is highly bioavailable.

It has been reported that the polyglutamyl form of food folates is absorbed in the jejunum as monoglutamyl folate after removal of the polyglutamyl chain by intestinal γ-glutamyl hydrolase [29], which is thereafter reduced and methylated in the enterocyte. The extent of passive diffusion of the reduced and methylated folate across the cell membrane is very limited [30], as it takes place only at high doses. To some extent folate is also absorbed in the colon, and it is suggested that colonic absorption may contribute significantly to total folate absorption [31], but it is still unknown that how relevant this absorption is for maintaining folate status. However, it has been shown for humans [32] that folates synthesized by colon bacteria are bioavailable. Absorbed folate is transported to the liver, which contains about half the body pool of folate [33] and retains 10–20% of absorbed folate due to the first-pass effect [34], while the rest is transported *via* the systemic circulation to body tissues. Some liver folate participates in the enterohepatic circulation and is secreted into bile [35]. However, most biliary folate is reabsorbed, supposedly to moderate between-meal fluctuations in folate supply to cells [36].

National Health and Nutrition Examination Survey data (NHANES 2013–2014) show that the majority population in the United States consume adequate amounts of folate. The average daily intakes of folate from foods range between 417 and 547 μg DFE per day for children between 2 and 19 years of age [37]. However, the mean dietary intakes for males who are 20 years and older are 602 μg DFE and for females, it is 455 μg DFE. It has been reported that although most of the people in the United States consume adequate amounts of folate, there are certain groups such as women of childbearing age and non-Hispanic black women who are still at risk of insufficient folate intakes. It has been further reported that about 35% of adults and 28% of children aged 1–13 years in the United States use supplements containing folic acid [38, 39] to meet their folate requirement. According to estimates of USDA-ARS [37], people aged 2 years and older who consume supplements containing folic acid get a mean of 712 μg DFE from those supplements. Several studies suggest that measurements of folate levels in the erythrocytes further confirm that most people in the United States have adequate folate status. Further there are also some analyses (NHANES 2003–2006), which shows that less than 0.5% of children (aged 1 to 18 years) have deficient folate concentrations in the erythrocytes [40]. Mean concentrations in this age group range from 211 to 294 ng/mL depending on age, dietary habits, and the amount of supplement use. In adults, mean erythrocyte folate concentrations range from 216 to 398 ng/mL, which also indicates the adequate folate status [39].

In contrast to this, there are also reports that some of the population groups are at risk of obtaining excess folic acid, primarily because of the folic acid they obtain from dietary supplements. About 5% of men and women aged between 51 and 70 years and men aged 71 years and older have folic acid intakes exceeding the prescribed upper limit of 1000 μg per day [38]. Furthermore, 30–66% of children aged 1–13 years who take folic acid-containing supplements have intakes of folic acid from both fortified food and dietary supplements exceeding the upper limit of 300–600 μg per day [39]. Almost all children aged 1 to 8 years who consume at least 200 μg/day folic acids from dietary supplements have total intakes that exceed the upper limit [40]. Despite so many reports of excess intakes of folic acid, there is *Vitamin B9 in Dark Green Vegetables: Deficiency Disorders, Bio-Availability, and Fortification… DOI: http://dx.doi.org/10.5772/intechopen.100318*

very little information available about the long-term effects of consumption of high folic acid doses in children [14].
