Folate functions as a coenzyme in single-carbon transfers in the synthesis of the building blocks of DNA, thymidylate and purines, certain neurotransmitters, phospholipids, and hormones (Bailey & Gregory, 2006). Folate deficiency can cause abnormalities in single-carbon metabolism. These abnormalities (e.g. hyperhomocysteinemia or DNA hypomethylation) may result in deleterious consequences, including increased risk for certain types of chronic diseases and developmental disorders (Bailey & Gregory, 1999). Folate deficiency in childhood may affect the neural development of children. An inadequate folate intake leads to a decrease in serum and erythrocyte folate concentrations and an increase in plasma concentrations of homocysteine, and ultimately to macrocytic anemia (Institute of Medicine, 2000).

Several Korean studies have indicated that dietary intakes of folate of reproductive-aged women were insufficient and that a large portion of the women were marginally folate deficient (Hyun et al., 1999; Lim et al., 2000). Most of folate status studies conducted in Korea focused on childbearing women. Although a few studies (Lim, 1999; Shin et al., 2005) have been conducted on the folate intakes of young Korean children, no study to date has reported biochemical measurements of plasma folate concentrations. Research is needed on the folate status of Korean young children. Therefore, the objectives of the present research were to estimate folate intakes and plasma concentrations of 2-6 y old children living in Kwangju, Korea.

Boys (n=24) and girls (n=30), 2-6 y old, living in Kwangju participated in this study, with the mean age being 4.1 y. The characteristics of the subjects are presented in Table 1. No differences in any of these characteristics of the subjects were observed by gender (p≥0.05). The mean (± SD) heights of 2 y, 3-5 y, and 6 y old children as categorized using the age groupings of the Korean Dietary Reference Intakes (DRIs) (The Korean Nutrition Society, 2005) were 88.2 ± 6.2, 107.7 ± 6.6, and 117.7 ± 5.2 cm, respectively, and their mean (± SD) weights were 12.2 ± 2.0, 17.9 ± 2.3, and 21.1 ± 3.1 kg, respectively. The mean energy intakes of 2 and 3 y old children were significantly lower (p<0.05) than those of 4, 5, and 6 y old children (Table 1). The mean (± SD) energy intakes of 2 y, 3-5 y, and 6 y old children were 957 ± 200, 1286 ± 305, and 1577 ± 297 kcal/d, respectively. The mean (± SD) intakes of proteins, carbohydrates, and total fats of the subjects were 48.6 ± 16.8, 192.9 ± 51.3, and 38.1 ± 14.5 g/d, respectively. Approximately 74% of the subjects met the Korean Acceptable Macronutrient Distribution Range (The Korean Nutrition Society, 2005) for carbohydrates, 93% for proteins, and 69% for total fats. The majority of the subjects reported that their intakes were typical. In this study, 9.3% of children had hemoglobin values of <cutoffs used to define anemia. The mean (± SD) values of hemoglobin of 2 y, 3-5 y, and 6 y olds were 123.7 ± 8.6, 124.7 ± 14.5, and 126.2 ± 7.6 g/L, respectively. In that they had hematocrit values <cutoffs, 7.4% of subjects were anemic. The mean (± SD) hematocrit values by Korean DRIs age groupings were as follows: 37.2 ± 2.6, 2 y olds; 37.3 ± 2.9, 3-5 y olds; and 37.7 ± 2.1%, 6 y olds.

Mean dietary intakes and plasma concentrations of folate in the children are also given in Table 1. No significant differences in folate intakes and plasma concentrations were observed by gender (p≥0.05). The mean (± SD) folate intake of the subjects was 146.7 ± 73.6 µg dietary folate equivalents (DFE)/d. One 4 y old boy and a 5 y old boy in the current study consumed supplements containing 0.2 µg folic acid daily. Mean (± SD) folate intakes of 2 y, 3-5 y, and 6 y old children were 97.4 ± 32.8, 149.5 ± 77.0, and 181.0 ± 68.7 µg DFE/d, respectively. The folate intakes of these 2 boys were >Korean Estimated Average Requirement (EAR) and plasma concentrations of the boys were >13.4 nmol/L, which is indicative of adequate folate status. The mean folate intakes of 2 and 3 y old children were significantly lower (p<0.05) than those of 5 and 6 y old children. The mean plasma folate concentration of all subjects combined was 19.2 ± 8.7 nmol/L, and there was no significant difference by age (p≥0.05). Mean (± SD) plasma concentrations of folate of 2 y, 3-5 y, and 6 y old children were 22.7 ± 12.5, 18.9 ± 8.3, and 16.8 ± 5.6 nmol/L, respectively. There was no significant correlation between folate intakes and plasma folate concentrations (p≥0.05). Also, no significant correlation was observed between plasma folate concentrations and hemoglobin and hematocrit values of the subjects in this study. Currently a few milk manufacturers in Korea add folate to some of the milk products they produce. The parents of all but 9 subjects reported the brand and type of milk consumed by their children, and these products did not contain added folate. Of these 9 subjects, one subject had a plasma folate concentration indicative of deficiency and two subjects (5 y old girl and 6 y old boy) had concentrations indicative of marginal folate status.

Fruits and vegetables provided 42% of the daily folate intake followed by grain products including flours at 36%. Meats, fish, eggs, and beans provided 14%; milk and milk products, 5%; and fats, seeds, and sweets, 3%. The predominant folate food sources, consumed by the children in the summer of 2005, were kimchi, toasted laver, cooked rice, eggs, watermelons, tomatoes, and muskmelons. Subjects reportedly consuming <Korean DRIs for folate got 42% of their folate from grain products including flours, 34% from fruits and vegetables, 14% from meats, fish, eggs, and beans, 7% from milk and milk products, and 3% from fats, seeds, and sweets. Subjects reportedly consuming ≥Korean folate DRIs got 31% of their folate from grain products including flours, 48% from fruits and vegetables, 14% from meats fish, eggs, and beans, 4% from milk and milk products, and 3% from fats, seeds, and sweets.

The percentages of subjects with less than adequate folate status using various criteria are given in Fig. 1. Fifty-seven percent of subjects consumed EARs for folate; this was 78% of 2 y, 51% of 3-5 y, and 66% of 6 y old subjects. Almost 60% of the children in this study consumed <folate EARs for USA/Canadians. One boy in the 4 y old group was folate deficient based on his having a plasma folate concentration <6.8 nmol/L (Sauberlich, 1975). Plasma folate concentrations of 24.1% of the subjects were between 6.8 and 13.4 nmol/L, which is representative of marginal folate status (Sauberlich, 1975). The percentages of subjects having marginal folate status subjects by Korean DRIs age groupings were as follows: 11%, 2 y; 26%, 3-5 y; and 33%, 6 y olds.

Dietary intakes and plasma concentrations of folate were determined in 54 healthy children living in Kwangju, Korea. The mean weight and height values of the children in the present study were similar to the means of USA children (Ogden et al., 2004) and Japanese children (Natsuchita et al., 2004). In the current study, 9.3% and 7.4% of the subjects had hemoglobin values and hematocrit values, respectively, <cutoffs used to define anemia, which were in line with the prevalence of anemia among preschool children in Korea (5.4%) (Park et al., 2005) and USA 2-5 y old children (12%) (Polhamus et al., 2004). Anemia is an indicator of poor nutrition and poor health (World Health Organization/United Nations Children's Fund, 2004). Thus, most of the Korean children in the present study were in apparent good health.

In the present study, the mean folate intake (146.7 µg DFE/d) was similar to the mean intakes of Spanish children aged 2-5 y old in the enKid Study, 1998-2000 (131.5 µg/d) (Serra-Majem et al., 2006), and German children aged 2-3 y and 4-6 y old in the Dortmund Nutritional and Anthropometric Longitudinally Designed Study (135.5 µg/d and 180.5 µg/d, respectively) (Sichert-Hellert & Kersting, 2004). However, the mean folate intake in the current study was lower than median folate intakes of USA children aged 1-5 y in the Third National Health and Nutrition Examination Survey (NHANES III), 1988-1994 (400 µg/d) (Lewis et al., 1999); this survey was conducted prior to mandatory fortification of enriched grain products by the Food and Drug Administration (FDA) in the USA. Fifty-seven percent of the subjects as categorized using the Korean DRIs age groupings consumed <EARs for folate for Koreans (The Korean Nutrition Society, 2005), and 59% of subjects consumed <USA/Canadian EARs (Institute of Medicine, 2000). The majority of USA children included in NHANES III consumed >USA/Canadian EARs for folate (Lewis et al., 1999). In Germany, 4.2% of 1-3 y old children (n=124) and 18% of 4-6 y old children (n=47) consumed <folate EARs for USA/Canadians (Kersting et al., 2000). Thus, the prevalence of inadequate folate intakes (<EARs) of Korean children in the present study was higher than those of other countries prior to fortification of grain products.

The accuracy of food composition data is important in estimating the intakes and adequacies of nutrients for population groups (Scrimshaw, 1997). Due to the limitations of traditional analytical methods, including the use of folate conjugase as the only enzyme, used in generating the food composition data for folate, the current database values underestimate actual folate contents. Several years ago, researchers started using trienzyme extraction (amylase and protease treatments in addition to folate conjugase) as the recommended method for measuring food folate content (Puwastien et al., 2005). It has been reported that current food folate composition data in Korea provides underestimations of folate intake of the Korean population (Han et al., 2005; Hyun & Han, 2001). According to the research of Han et al. (2005), folate intakes of college students (n=106) calculated using analyzed folate values were 1.8 times higher than the intakes calculated using the current Korean food composition database. Also, an average folate loss of 29% was indicated by cooking (Han et al., 2005). For the reasons indicated above, it is likely that estimates of folate intakes in this study could be underestimates of actual intakes.

In the current study, major contributors of folate intake were fruits and vegetables providing 42% of the daily folate intake and grain products including flours supplied 36%. In a study of folate intake conducted by Han et al. (2005), vegetables were the major folate source contributing 38-44% of intake of Korean college students. Among vegetables, kimchi was predominant folate source in the study of Han et al. (2005). In the current study, the predominant folate food sources, consumed by the children during summer, 2005, were kimchi, toasted laver, cooked rice, eggs, watermelons, tomatoes, and muskmelons, which are similar with the major folate food sources of Korean college students (Han et al., 2005). Rice is a staple food in Korea. Although the folate content of rice (12 µg/100g; The Korean Nutrition Society, 2002) is not as a high as those of vegetables, a group of grain products and flours including rice provided a considerable portion of the folate intake of the Korean children of the current study.

The mean plasma folate concentration of Korean children aged 2-6 y was 19.2 nmol/L, which is higher than the mean of 2-5 y old Austrian children (10 nmol/L) (Huemer et al., 2006), but in line with the mean of 2-5 y old Dutch children (24 nmol/L) (van Beynum et al., 2005) and the median (21 nmol/L) of 4-8 y old USA children in NHANES III, 1988-1994 (Institute of Medicine, 2000). One subject (1.9%) in this study had a plasma folate concentration <6.8 nmol/L, which is indicative of folate deficiency (Sauberlich, 1975). In the Mexican National Survey of 1999, approximately 5% of the children were folate deficient (Villalpando et al., 2003), and 2% of Costa Rican children <6 y old were folate deficient (Allen, 2004). Sixteen percent of USA children aged ≤5 y old in NHANES III had serum folate concentrations indicative of deficiency (Pfeiffer et al., 2005). Approximately 24% of subjects in the current study had plasma concentrations of 6.8-13.4 nmol/L, which is interpreted as marginal status of folate (Sauberlich, 1975). The prevalence of marginal folate status of children in this study was higher than that of Guatemalan children (1%) aged 8-12 y (Rogers et al., 2003), and that of Costa Rican children (9%) <6 y old (Allen, 2004).

Folate fortification may be of benefit to women of childbearing age in increasing their intake of folate and thereby reduce their risk of a pregnancy affected by a neural tube birth defect. Also, the fortification may improve folate nutrition for the general population (Institute of Medicine, 2000). In the USA, FDA has required since 1998 that enriched grain products be fortified with folic acid at a concentration of 140 µg/100 g cereal grain (Food and Drug Administration, 1996), and the folate status of the USA population has improved as indicated by increased plasma folate and red blood cell concentrations (Ganji & Kafai, 2006; Pfeiffer et al., 2005). The median folate intake of 1-5 y old USA children in NHANES III 1988-1994, prior to folate fortification was 400 µg DEF/d (Lewis et al., 1999), while in NHANES 2001-2002, after folate fortification, the median intakes of 1-3 and 4-8 y old USA children were 369 µg DFE/d and 501 µg DFE/d, respectively (Moshfegh et al., 2005). The prevalence of deficient serum folate concentrations (<6.8 nmol/L) decreased from 16% in NHANES III 1988-1994 to 0.5% in NHANES 1999-2000 for the USA population (Pfeiffer et al., 2005). Also, the prevalence of neural tube birth defects decreased by 19% in USA, when pre-folic acid fortification data were compared with the post-folic acid fortification data (Honein et al., 2001). Australia, Chile, Hungary, and New Zealand are fortifying >200 µg folate in 100 g flour (Oakely et al., 2004). However, in Korea, folate fortification is not currently required in food products. Whole grains are imported for use in manufacturing 98% of the flours consumed in Korea (Woo, 2006), and the manufacturers typically do not add folate during processing. Some food companies in Korea have fortified folate voluntarily along with other nutrients in their breakfast cereal products, milk, and soymilk. The parents of most milk and soymilk drinkers in this study indicated that their children drank non-fortified milk or soymilk. In this study, none of the subjects consumed any breakfast cereal products. Subjects consuming <Korean EARs for folate got more of their folate from grain products including flours than subjects reporting consuming ≥Korean EARs for folate. According to Han et al. (2005), 19-36% folate losses were indicated during the cooking of grain products which are one of major folate sources. Therefore, folate fortification of grain products including flours may improve folate intakes and plasma concentrations of Korean children, women of childbearing age, and the population in general.

In conclusion, approximately 60% of subjects had inadequate folate intakes, that is <Korean folate EARs. Although the prevalence of folate deficiency was low based on plasma concentrations <6.8 nmol/L, one-quarter of Korean children in the current study had marginal status of folate, which is higher than the prevalence of many other countries. Some young children in Korea may be at risk of inadequate folate status. Thus, increased consumption of folate-rich foods such as liver, yeast, legumes, dark green leafy vegetables, and fortified food products such as breakfast cereals, milk, and soymilk can improve the folate status of young children in Korea. The grain product intakes of young children in the current study were considerable. Folate fortification of grain products would most likely improve the folate status of Korean children, as well as other population groups.