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INTRODUCTION
It is necessary to properly supply nutrients according to the developmental stage of children [1]. Parents should pay attention to supply enough nutrients for children especially during the supplemental feeding and early childhood period. Adequate supply of essential minerals should also be paralleled for proper growth and development of children [2].
Several minerals such as calcium, iron, zinc, copper, and selenium are particularly important for the normal growth of young children. Calcium is necessary for the formation of the skeleton, muscle contraction, blood coagulation and membrane integrity [34]. Iron deficiency is common in children and can have negative consequences in terms of mental, motor and behavioral development as well as anemia [5678]. Zinc deficiency is related with growth faltering, increased risk of infection and delayed motor development [910]. Copper plays a role in iron metabolism through ceruloplasmin, a copper-dependent enzyme that oxidizes iron to be transported to the body tissues [11]. Selenium is an intrinsic component of antioxidant enzyme glutathione peroxidase that works as a cell membrane protector against lipid peroxidation [12].
In order to evaluate the body mineral status of children, collection and analysis of blood or hair of the children are needed. Hair mineral analysis has the advantage of being easy to store and collect samples, but has not been used much in children [13141516]. In this study, a dietary intake and hair mineral analysis of Korean young children were conducted to evaluate mineral nutrition status of the children.
MATERIALS AND METHODS
Subjects
A total of 55 children (31 male and 24 female) who newly visited the Pediatric Nutrition Clinic at the Seoul National University Hospital between January 2012 and December 2013 for nutritional counselling, regardless of the growth status, were included. The subjects were divided into three age groups; infants (6 months to 1 year), toddlers (1 to 2 years), and preschoolers (3 to 5 years). Weight for age z-scores and weight for height z-scores were calculated using the least mean square method adjusted for age and sex according to the 2007 Korean National Growth Charts [17]. Underweight was defined as weights for age z-scores below -2 standard deviations.
Children with underlying organic diseases or those who had taken multivitamin or iron or zinc supplements in the past 3 months were excluded from the study.
The study was conducted with the approval of the Institutional Review Board of Seoul National University Bundang Hospital (B-1503-292-110).
Physical measurements and dietary intake survey
Height was determined using a fixed scale measuring device and was measured to the nearest 0.1 cm. Weight was measured to the nearest 0.1 kg using a digital scale calibrated prior to each measurement. Children's dietary intake data were estimated using one-day 24-hour recall method by an interview with their mothers. The dietary data were assessed using a computerized nutrient-intake assessment software program (CAN-Pro 4.0; Korean Nutrition Society, Seoul, Korea). Calcium, iron, zinc, copper and selenium intake data were compared with the Estimated Average Requirements (EAR) of the 2010 Korean Dietary Reference Intake (KDRI) [18].
Laboratory analysis
The hair mineral analysis was performed by Trace Elements Inc. (Dallas, TX, USA) with hair samples sent through the Korean branch. After washing the samples with acetone, water, and extran (1% v/v), aliquots of the samples were wet-ashed with HNO3. The hair solution was analyzed by a Perkin-Elmer Mass Spectrometer (Sciex Elan 6100; Perkin-Elmer Corp., Foster City, CA, USA) [19]. All hair mineral levels were reported in percent of milligrams (mg%, milligrams per 100 grams of hair). Serum samples were analyzed for ferritin by the immunoradiometric assay (Diagnostic Products Inc., Los Angeles, CA, USA) and for calcium and iron by atomic absorption spectrophotometry (Perkin Elmer 300 Instrument).
Statistical analysis
The data were analyzed using PASW Statistics version 18.0 (IBM Co., Armonk, NY, USA). They were checked for normality using Kolmogorov-Smirnov test and residual data plots were examined for determination of the homogeneity of variance. The data were expressed as mean and standard deviation for normally distributed variable and median (percentile 25, percentile 75) for non-normally distributed variable. Comparisons among groups were done by ANOVA or Kruskal-Wallis nonparametric test. Scheffe's test with means or ranks was used as a post-hoc test. The value of p<0.05 was chosen as the level of statistical significance.
RESULTS
General characteristics and macro-nutrient intakes of the subjects
The general characteristics of the 55 subjects are listed in Table 1. The median ages of the children were 0.82 (infants), 1.46 (toddlers) and 4.66 (preschoolers) years old for each age group. The median heights and weights were 67.6 cm and 7.0 kg in infants, 77.5 cm and 9.1 kg in toddlers, and 98.0 cm and 13.9 kg in preschoolers, respectively. Underweight was noted in 42.9% of infants, 35.1% of toddlers, and 36.4% of preschoolers in this study. The median z-scores of the children's height and weight were –1.4 and –1.8, which were not significantly different among the age groups.
Macro-nutrient intakes of the subjects are listed in Table 2. The mean energy intakes of the subjects were 730.3 kcal (infants), 994.3 kcal (toddlers), and 1,482.9 kcal (preschoolers) for each age group. Energy intake was significantly higher in preschoolers than in infants and toddlers. Carbohydrate, protein and fat intake also increased with the energy intake increment. The mean energy intake percentage was 104.3%, 99.4%, and 105.6%, respectively, and was not different by the age group. The ratio of carbohydrate-eneray:fat-energy:protein-energy was 57.9%:28.3%:14.1% among infants, 59.2%:24.4%:15.8% among toddlers, and 62.2%: 28.6%:15.3% among preschoolers, respectively.
Mineral intakes of the subjects
Mineral intakes of the subjects are listed in Table 3. Calcium intakes of the children were not different by age group. Meanwhile, iron, zinc, copper, and selenium intakes increased with age.
Percentages of children who consume minerals less than the EAR of the age are listed in Table 4. For infants, only the EAR of iron and zinc are established by the KDRI committee. In this study, 28.6% of infants showed the intake of iron less than the EAR, but the intake of zinc were all above the EAR. For toddlers and preschoolers, 37.8% of toddlers and 54.5% of preschoolers had the intake of calcium less than the EAR, and 10.8% of toddlers and 9.1% of preschoolers had the intake of iron less than the EAR. In the cases of zinc, copper, and selenium, only 0-5% of toddlers and none of the preschoolers consumed less than the EAR.
Hair mineral content of the subjects
Hair mineral content are listed in Table 5. Median hair calcium was significantly lower in toddlers than in infants. Median hair iron and copper contents of toddlers and preschoolers were significantly lower than those of infants. Median zinc and selenium contents were not different by age.
Serum parameters of the subjects
Serum parameters of the subjects are listed in Table 6. Serum calcium levels of the preschoolers were significantly lower than those of infants. Ferritin, the storage form of iron, and serum iron levels were not different among the age groups, but serum ferritin levels were relatively lower in toddlers and preschoolers than in infants.
DISCUSSION
Energy requirements of young children are difficult to analyze due to the large variation in individual growth rate and body composition. Mean energy intakes of children in this study were within the normal intake range of the estimated energy requirement for each age (99.4-105.6%). Mean carbohydrate-, protein-, and fat-energy percentages were 58-62%, 14-16%, and 24-29%, respectively. It was within the proper proportion (55-70% carbohydrate, 7-20% protein, and 15-35% fat) recommended by the KDRI [18].
The mean daily calcium intake of Korean children from Korean National Health and Nutrition Examination Survey (KNHANES) 2007 to 2010 was 446.2 mg at 1-2 years of age, and 428.3 mg at 3-5 years of age [20]. The mean daily calcium intake in the present study was 548.1 mg at 6 months-1 year of age, 464.9 mg at 1-2 years of age, and 472.2 mg at 3-5 years of age. Therefore, children from this study had a little bit higher calcium intake than the national sample. The proportion of children who eat less calcium than the EAR was 37.8% for toddlers and the proportion increased to 54.5% for preschoolers in this study. The report of the KNHANES 2007 to 2010 also showed similar results with this study in that the proportion of children who ate less calcium than the EAR were 53.9%, 55.2%, and 65.6% at 1-, 2-, and 3-years of age, respectively [20].
It is essential to consume a sufficient amount of calcium in childhood for maximum accumulation of bone mass, as well as for height growth [4]. In this study, median hair calcium level was significantly lower in toddlers than in infants. Therefore, it may be necessary to promote consumption of more dairy products from the supplemental period to improve calcium status of children.
The daily iron intake in the present study was 6.5 mg at 6 months-1 year of age, 7.3 mg at 1-2 years of age, and 10.7 mg at 3-5 years of age. The daily iron intake of children from KNHANES 2007 to 2010 was 5.5 mg, 5.9 mg, and 6.1 mg at 1-, 2- and 3- years of age, respectively [21]. Therefore, children from this study had higher iron intake than the Korean national sample. The proportion of infants who consume less than the EAR of iron in this study was 28.6% for 6 months-1 year old infants, 10.8% for toddlers and 9.1% for preschoolers. Meanwhile, the 2007 to 2010 KNHANES report showed that 52.0%, 48.7%, and 48.4% of the 1-, 2-, and 3-year old children did not meet the Korean EAR of iron [21].
Iron-deficiency anemia is one of the most common nutritional disorders worldwide [56]. Young children are especially vulnerable to iron deficiency because their diet is low in iron and the required amount of iron is high due to rapid growth [22]. Iron is also important for a normal brain development, the immune system, body temperature regulation, the prevention of stroke and thrombosis and social and emotional development [6782324].
In this study, hair iron content of toddlers and preschoolers were significantly lower than that of infants. In addition, serum ferritin concentrations of toddlers and preschoolers also showed a decreasing tendency compared to infants. It is assumed that the lack of iron intake during supplemental feeding period (6 months-1 year of age) might have decreased iron storage, hence resulted in a lower accumulation of iron in hair. Gürgöze et al. [13] also showed that hair and serum iron content were lower in children with iron deficiency. Therefore, it is important to emphasize the supply of iron-rich foods to children from early supplemental period to improve their iron status.
Copper is involved in the metabolism of iron because ceruloplasmin is involved in the oxidation of iron [11]. A previous study in children showed that the concentration of hair copper was lower in person with iron deficiency [13]. In this study, copper intake of the children was normal, but the hair copper content of toddlers and preschoolers were significantly lower than that of the infants. It is possible that the decreased hair copper level in older children is related with copper deficiency secondary to iron deficiency, but further studies are necessary to clarify the reasons of decreased hair copper level in these children.
The hair mineral content of the children in this study was within the normal range of reference values for the Korean children suggested by Park et al. [25]. Song et al. [14] also measured the hair iron, zinc, copper and selenium from Korean autistic children and the values were similar to our results.
There were some limitations in our study because we recruited small numbers of the subjects and collected only one-day dietary recalls instead of two or more inconsecutive days of dietary intake to estimate usual individual intake [26]. Despite these limitations, we propose that the current study provides meaningful data regarding dietary intake and hair mineral status of young Korean children.
In summary, hair calcium, iron, and copper concentrations were lower in toddlers and preschoolers than in infants. Insufficient dietary intake of calcium and iron seems to be related with decreased hair mineral contents in young children. Further studies are necessary to clarify the mineral nutrition status of the children.
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