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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 31  |  Issue : 2  |  Page : 467-473

Serum vitamin D level in obese school-aged children


1 Department of Pediatrics, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Clinical Pathology, Faculty of Medicine, Menoufia University, Menoufia, Egypt
3 Department of Pediatrics, Tala Central Hospital, Menoufia, Egypt

Date of Submission28-Dec-2016
Date of Acceptance01-Mar-2017
Date of Web Publication27-Aug-2018

Correspondence Address:
Sara M Zayed
Department of Pediatrics, Tala Central Hospital, Tala, Menoufia
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mmj.mmj_667_16

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  Abstract 


Objective
The aim of this study was to assess vitamin D status in obese school-aged children and to correlate vitamin D levels with other clinical and laboratory investigations.
Background
Obesity and vitamin D deficiency have been classified as epidemics throughout the world; many studies have shown that vitamin D status and fat mass are inversely correlated.
Patient and methods
This study was carried out on 80 children ranging in age from 6 to 18 years divided according to BMI into two groups: an obese group [40 children (12 boys and 28 girls)] and a control group [40 apparently healthy children (17 boys and 23 girls)]. All children were subjected to a full assessment of history, clinical examination, and laboratory investigations including complete blood picture, qualitative C-reactive protein (CRP), fasting lipid profile (serum cholesterol, triglycerides, high-density lipoprotein, low-density lipoprotein), serum calcium (total), phosphorus, alkaline phosphatase, and serum 25(OH)-vitamin D.
Results
Our results showed that obese children had significantly higher values than the controls on all anthropometric measurements except the upper/lower segment ratio; they had significantly higher blood pressure, lower levels of hemoglobin, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and higher levels of all parameters of the lipid profile except high-density lipoprotein, which was lower. Positive CRP was detected in 80% of the children in the obese group, with 100% negative CRP in the control group. They had significantly lower 25(OH)-vitamin D than the controls; vitamin D deficiency was detected in 52.5% of obese children, and 47.5% of these children had vitamin D insufficiency. However, 52.5% of the controls had 25(OH)-vitamin D insufficiency. A significantly positive correlation was detected between triceps skinfold thickness and fasting serum cholesterol in the obese group.
Conclusion
Obese children are prone to hypertension, dyslipidemia, microcytic hypochromic anemia, inflammatory process, and vitamin D deficiency; apparently healthy children may have undiagnosed vitamin D insufficiency.

Keywords: obesity, school children, vitamin D


How to cite this article:
Tawfik MA, Barseem NF, Khodeer SA, Zayed SM. Serum vitamin D level in obese school-aged children. Menoufia Med J 2018;31:467-73

How to cite this URL:
Tawfik MA, Barseem NF, Khodeer SA, Zayed SM. Serum vitamin D level in obese school-aged children. Menoufia Med J [serial online] 2018 [cited 2018 Sep 19];31:467-73. Available from: http://www.mmj.eg.net/text.asp?2018/31/2/467/239763




  Introduction Top


Childhood overweight and obesity is one of the most serious public health challenges of the 21st century. The problem is global and is becoming prevalent in many low-income and middle-income countries, particularly in urban settings. The prevalence of obesity has increased at an alarming rate [1].

Excess body fat in children and adolescents can lead to a variety of clinical conditions and psychosocial disorders such as nonalcoholic fatty liver disease, sleep apnea, type 2 diabetes mellitus, bronchial asthma, cardiovascular disease, hypercholesterolemia, glucose intolerance and insulin resistance, skin conditions, menstrual abnormalities, impaired balance, orthopedic problems, and poor learning skills, which can lead to social discrimination. All of these conditions contribute toward an increased morbidity and/or premature mortality [2].

Vitamin D deficiency is becoming a global public health problem, although it is largely unrecognized [3]. It is a problem highly prevalent worldwide, especially among adolescents [4], but it is also recognized in children of all ages [5].

Our study was carried out to assess vitamin D status in obese school-aged children and to correlate vitamin D levels with other clinical and laboratory investigations.


  Patients and Methods Top


This study was carried out on 80 children aged 6–18 years attending the Pediatric Outpatient Clinic in Tala Central Hospital and Menoufia University Hospital during the period from March 2016 to August 2016 who were divided according to their BMI plotted on the WHO reference 2007 into two groups:

Group 1 (obese group): Included 40 obese children (12 boys and 28 girls) with BMI more than 2 SD above the WHO growth reference median. Their mean age was 11.35 ± 3.21 years.

Group 2 (control group): Included 40 apparently healthy children (17 boys and 23 girls) with BMI falling between −2 and 1 SD or 3rd–85th percentile. Their mean age was 10.43 ± 1.81 years and were well matched in age, sex, and socioeconomic status.

(According to the WHO reference 2007, obesity in children older than 5 years is defined as BMI for age greater than 2 SD above the WHO growth reference median and overweight as BMI for age greater than 1 SD above the WHO growth reference median) [6].

Inclusion criteria

Inclusion criteria were as follows:

  • Children aged between 6 and 18 years of age
  • Primary obesity
  • Both sexes.


Exclusion criteria

Exclusion criteria were as follows:

  • Secondary causes of obesity – for example, endocrinal and genetic obesity
  • Children with chronic debilitating diseases – for example, hepatic or renal diseases, diabetes mellitus, chronic lung diseases, hypertension, rheumatic, and congenital heart diseases
  • Children with metabolic rickets, calcium metabolism disorders, malabsorptive disorders (Crohn's disease, cystic fibrosis, and celiac disease), and cancer
  • Long-term therapy of vitamin D or multivitamin supplements, anticonvulsants, or systemic glucocorticoids.


Ethical criteria

The study was approved by the Ethical Committee of Menoufia Faculty of Medicine. Written informed consent was obtained from the guardians of each participant after explaining the aim of the study.

All children were subjected to the following:

  • Full assessment of history
  • Complete clinical examination with a special focus on:


    1. Blood pressure measurements:


    2. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) measurements were obtained and the results were plotted on sex-specific SBP and DBP percentiles

    3. Anthropometric measurements:


      1. Standing height (cm)
      2. Sitting height (cm)
      3. Weight (kg)
      4. BMI [weight (kg)/height (m 2)]
      5. Waist/hip ratio (WHR)
      6. Upper/lower segment ratio
      7. Triceps skinfold (TSF) thickness (mm).


      BMI and height were plotted on WHO reference charts for anthropometric measurements for children 5–19 years old [6] and weight was plotted on Egyptian weight-for-age percentile for boys and girls 2–21 years [7] because weight-for-age percentiles are not available beyond 10 years of age in WHO reference charts as this indicator does not distinguish between height and body mass in an age period where many children are experiencing pubertal growth spurt and may appear to have excess weight (by weight-for-age) when in fact they are just tall.

      TSF thickness was measured using Baseline skinfold (Fabrication Enterprises, Inc, White Plains, New York, USA) caliper between the tip of the olecranon process of the ulna (elbow) and the acromion of the scapula (shoulder), and the results were plotted on reference percentiles for triceps and subscapular skinfold thickness in US children and adolescents [8].

    4. Cardiac examination
    5. Chest examination
    6. Other systemic review


  • Laboratory investigations including the following:


    1. Complete blood picture
    2. Qualitative measurement of C-reactive protein (CRP)
    3. Fasting lipid profile assessment:


      1. Cholesterol
      2. Triglycerides
      3. High-density lipoprotein (HDL)
      4. Low-density lipoprotein (LDL) [9]


    4. Work-up for calcium metabolism (serum calcium, phosphorus, alkaline phosphatase) [10]
    5. Serum 25(OH)-vitamin D level by enzyme-linked immunosorbent assay using DRG 25(OH)-vitamin D (total) enzyme-linked immunosorbent assay kits (catalog number EIA-5396; DRG international, Inc., USA) [11]


Three categories of vitamin D were recognized [12]:

  • Category 1: Deficient [serum level of 25(OH)-vitamin D <30 nmol/l]
  • Category 2: Insufficient [serum level of 25(OH)-vitamin D between 30 and <50 nmol/l]
  • Category 3: Adequate [serum level of 25(OH)-vitamin D >50 nmol/l].


Statistical analysis

The results were statistically analyzed using an IBM personal computer and statistical package SPSS, version 20, for Windows (SPSS Inc., Chicago, Illinois, USA). Statistics were calculated in terms of mean, range, standard deviation, percentage, and Student's t-test, which is a test of significance used for comparison between two groups of quantitative variables; the c2-test was used to study the association between two qualitative variables. A P value less than 0.05 was considered significant, P value less than 0.01 was considered highly significant, and P value greater than 0.05 was considered insignificant [13].


  Results Top


A total of 80 children were studied; 40 of these children were of normal weight and 40 were obese according to their BMI. There was no significant difference in age, sex, or place of residence between the children in the obese group and the control group. The age of the studied children ranged from 6 to 18 years, with a mean age of 11.35 ± 3.21 years in the obese group and 10.43 ± 1.81 years in the control group [Table 1].
Table 1: Demographic data of the studied groups

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Obese children had significantly higher parameters than controls in weight, standing and sitting height, WHR, and TSF thickness, with no significant difference in the upper/lower segment ratio. SBP and DBP were significantly higher in obese children than the controls [Table 2].
Table 2: Anthropometric and blood pressure measurements of the studied groups

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Obese children had significantly lower levels of hemoglobin, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration than the controls, whereas no significant difference was observed between obese and control groups in the white cell or platelet cell counts [Table 3].
Table 3: Complete blood counts of the studied groups

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Obese children had significantly higher levels of cholesterol, triglycerides, and LDL, whereas HDL was significantly lower in obese children than the controls [Table 4].
Table 4: Lipid profile in the studied groups

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There were no significant differences between obese children and the controls in serum calcium, phosphorus, or alkaline phosphatase. However, there was a significantly higher prevalence of positive CRP in obese children than the controls; positive CRP was detected in 80% of children in the obese group, with 100% negative CRP in the control group [Table 5].
Table 5: Serum calcium, phosphorus, alkaline phosphatase, and C-reactive protein levels of the studied groups

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Obese children had significantly lower levels of 25(OH)-vitamin D than the controls; the majority of the obese children (52.5%) had 25(OH)-vitamin D deficiency whereas 47.5% of them had 25(OH)-vitamin D insufficiency. However, 52.5% of the controls had 25(OH)-vitamin D insufficiency and 47.5% had adequate levels of 25(OH)-vitamin D [Table 6].
Table 6: Serum 25(OH)-vitamin D levels of the studied groups

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There was a significant positive correlation between TSF thickness and cholesterol level, whereas no significant correlation was found with other parameters of the lipid profile [Table 7].
Table 7: Correlation between triceps skinfold thickness (mm) and lipid profile in obese children

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  Discussion Top


One growing, active area of research is the association between vitamin D deficiency and childhood obesity. Individually, each has been classified as an epidemic throughout the world, and both share some common risk factors including poor diet and inactivity [14].

In our study, in terms of anthropometric measurements, the mean weight of the children in the obese group was significantly higher than that of the control group; we also observed that obese children were significantly taller than the controls, in agreement with Ajala et al. [15], who found that obese children were taller than normal-weight children. This can be explained by earlier maturation of heavier children.

Zhu et al. [16] agreed that BMI, waist circumference, and WHR were significantly higher in obese children than the controls in a study that included 2243 school children aged 7–17 years. Yilmaz et al. [17] reported that all skinfold thicknesses were two times higher in obese children in a study that included 178 school children aged 6–16 years in Turkey. The mean SBP and DBP were significantly higher in the obese group, in agreement with Babinska et al. [18], who analyzed the association between obesity and severity of hypertension in a total of 109 patients with primary obesity aged 7–18 years and found a significant association between obesity and hypertension.

Similar findings were obtained by Kapil and Sareen [19], who reported a higher prevalence of anemia among overweight and obese children in the age group of 5–18 years in NCT, Delhi. Foschini et al. [20] agreed that there was no difference between obese children and the controls in the leukocytic count, but reported a higher platelet count in obese children than the controls, and attributed this to higher platelet activation and aggregation, which are central processes in the pathophysiology of cardiovascular disease associated with obesity.

Obese children had significantly higher levels of all parameters of the lipid profile, except HDL, which was lower in obese children than the controls, in agreement with Reinhr et al. [21], who studied cardiovascular risk in 1004 overweight children and adolescents (aged 4–8 years) and reported that 27% of the studied children showed increased total cholesterol, 26% increased LDL-cholesterol, 20% increased triglycerides, and 18% decreased HDL-cholesterol. The reduced level of HDL in the obese group could be explained by increased numbers of remnants of chylomicrons and very LDL together with impaired lipolysis. The increased number of triglyceride-rich lipoproteins results in increased cholesterylester-transfer protein activity, which exchanges cholesterolesters from HDL for triglycerides from very LDL and LDL [22]. Moreover, lipolysis of these triglycerides-rich HDL occurs by hepatic lipase resulting in small HDL with a reduced affinity for apo A-I, which leads to dissociation of apo A-I from HDL. This will ultimately lead to lower levels of HDL and a reduction in circulating HDL particles with impairment of reversed cholesterol transport [23]. This prevalence of dyslipidemia and hypertension in obese children in our study is considered a risk factor for cardiovascular disease later in life [24].

In agreement with Reinehr et al. [25], there were no significant differences between obese children and the controls in serum calcium, phosphorus, or alkaline phosphatase; low serum 25(OH)-vitamin D levels were not associated with a concomitant reduction in serum calcium because secondary hyperparathyroidism not only increases mobilization of calcium from the skeleton but also increases calcium reabsorption in the kidney. Thus, it is not expected that calcium levels will decline in patients with vitamin D deficiency until most of the calcium has been depleted from the skeleton. However, there was a significantly higher prevalence of positive CRP in obese children than the controls; positive CRP was detected in 80% of obese children versus 100% negative CRP in the controls in agreement with Michael et al. [26]. This state of inflammation in obese children could be explained by the evidence that adipose tissue acts as an active endocrine organ that stimulates inflammatory cascades [27]. Previous research used ultrasound techniques to show that increased CRP seems to be related to vascular intima media thickness in children and early atherosclerotic changes related to inflammation [28]. This raises concerns about the risk for long-term cardiovascular disease in the entire population of overweight children.

In the current study, the majority of the obese children, 52.5% of them, had 25(OH)-vitamin D deficiency, whereas 47.5% had 25(OH)-vitamin D insufficiency. In USA, Alemzadeh et al. [29] reported hypovitaminosis D in 74% of a group of 127 obese children aged 13.0 ± 3.0 years and identified vitamin D deficiency in 32.3% and vitamin D insufficiency in 41.7% of these children. Roth et al. [30] assessed serum 25(OH)-vitamin D serum concentrations in 125 obese German children aged 11.9 ± 2.7 years and reported that 76% were found to be 25(OH)-vitamin D deficient. It was also found that 25(OH)-vitamin D levels were inversely related to BMI, waist circumference, total fat mass, and percentage of fat mass in a group of adolescents in Augusta, Georgia; this inverse relationship was also reported by Rajakumar et al. [31]. However, it is not clear whether hypovitaminosis D contributes toward or is a consequence of obesity or whether there are regulatory interactions between excess adiposity and vitamin D activity; in 2013, a bidirectional genetic study, which limits confounding, suggested that higher BMI leads to lower 25(OH)-vitamin D, with the effects of lower 25(OH)-vitamin D on BMI likely to be small [32]. This study concluded that obesity is a cause not a consequence of vitamin D deficiency. Although the mechanisms for the lower 25(OH)-vitamin D concentrations in obese children are not fully described, there may be several explanations including sequestration of vitamin D in the subcutaneous body fat and its consequent reduced bioavailability [33], decreased sun exposure because of limited physical activity [34], and reduced activation [35]. Another explanation was provided by Drincic et al. [36], who reported that a volumetric dilutional model accounted for essentially all the variability in serum 25(OH)-vitamin D concentrations attributable to obesity and concluded that once serum 25(OH)-vitamin D concentrations in obese individuals are adjusted for body size, there is no longer a difference between obese and nonobese individuals.

However, a considerable percent (52.5%) of the controls had 25(OH)-vitamin D insufficiency; previous studies agreed that there is a state of hypovitaminosis D among healthy children and adolescents. This percent of controls with 25(OH)-vitamin D insufficiency is approximately the same as that reported in Lebanon by El-Hajj Fuleihan et al. [37], Çizmecioğlu et al. [38], and similar results were also found in other countries as follows: 78% in France [39], 42% in Boston [40], 42.5% in Beijing [41], 47% in Greece [42], 46.2% in Iran [43], 29% in Switzerland [44], 65% in Finland [45], and in Turkey, where the hypovitaminosis D rate was 59.4% among adolescents in Izmir, which is a sunny seaside city [46]. These studies done in different countries detected vitamin D deficiency among apparently healthy non obese children despite living at different latitudes and even in those living in sunny areas, so other possible risk factors for this deficiency should be searched [47].

A significantly positive correlation was found between TSF thickness and serum cholesterol level; this is in agreement with Sanlier and Yabanci [48], who examined the relationship between body composition and blood lipid concentrations and reported a positive correlation between TSF thickness and serum cholesterol level, LDL, and triglycerides. A significant correlation was also detected between TSF thickness, SBP, and DBP; this positive correlation was reported previously by Souza et al. [49]. These results confirmed the role of the use of anthropometric measurements including TSF thickness to follow up obese children for cardiovascular risk factors, for example hypertension and dyslipidemia together with other clinical and laboratory investigations used routinely to reduce cardiovascular risks in the future.


  Conclusion Top


Obese children are prone to several risks including hypertension, dyslipidemia, microcytic hypochromic anemia, inflammatory process, and vitamin D deficiency, raising concerns of the additive effect of these risks on the cardiovascular system with a subsequent reduction of quality of life in obese children. However, a considerable percentage of apparently healthy children were found to have vitamin D insufficiency; thus, we recommend fortification of food with vitamin D to overcome this problem.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Tables

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