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Evaluation of selected mineral concentrations in overweight and obese adolescents

Sandhya H P^1*, Mohammed Jaffer², Amin Dhanush Jayananda³, Noorjehan Begum⁴

¹Assistant Professor, ³UG Student, Professor and HOD, Department of Physiology, VIMS, Ballari- 583104, Karnataka, INDIA.

Email: sandyviju83@gmail.com, mdjafferkp@gmail.com

Research Article

 

Abstract               Background: Obesity is increasing all over the world in adolescents due to a decrease in physical activity and change in lifestyle. Studies showing an association between serum concentrations of minerals and insulin resistance in overweight and obese adolescents are lacking. Aims and objectives: To assess serum concentrations of calcium, magnesium and fasting blood glucose levels in over weight (and obese) adolescents and to determine the association between serum mineral concentrations with fasting blood glucose in them. Materials and Methods: A case control study was done involving 30 apparently normal overweight (> 95^th percentile) aged between 12 – 19 years (cases), 30 age and gender matched normal weight (5^th – 84^th percentile) adolescents(controls) were randomly selected. Serum concentrations of calcium (Arsenazo III method), magnesium(colorimetric xylidyl blue method) and fasting blood glucose (trinder’s method) were assessed for both the groups along with anthropometric measurements height (cm), weight (kg), waist circumference (cm), BMI (kg/Sq.m) and the recording of pulse rate (manual) and blood pressure (mercury sphygmomanometer). Data was tabulated and statistically analyzed using SPSS software. Results and conclusions: Serum concentrations of calcium, magnesium and fasting blood glucose were statistically similar and within normal limits in both groups. However a significantly negative correlation was found between serum calcium and BMI, PR, SBP, FBS in cases. In contrast a significantly positive correlation was observed between serum magnesium and PR, SBP, and FBS in them; the cause of which is not known. Hence further studies are needed in this regard to confirm the observations obtained in this study.

Key words: FBS, overweight adolescents, serum calcium, serum magnesium.

 

INTRODUCTION

Prevalence of obesity in children and adolescents is increasing all over the world. Obesity is strongly associated with development of insulin resistance(IR) and CVS diseases even in normoglycemic adults. Hence overweight and obese adolescents are predisposed to a premature progression to high BP and high blood glucose levels.¹ Studies indicate an excessive body fat associated with micronutrient deficiencies.² Intracellular calcium plays an important role in modulating the regulatory factors involved in hypertension, IR and obesity.³ Hence calcium deficiency may increase risk of obesity. A strong relationship between magnesium and insulin action is already well documented. Low serum and intracellular magnesium concentrations are known to be associated with the development of IR, impaired glucose tolerance and decreased insulin secretion. In addition to this, lower dietary magnesium and lower serum magnesium are associated with the increased risk for type 2 diabetes.⁴ But, there is a lack of data concerning the status of micronutrients and their relationship with IR and body composition in adolescents. Hence the present study was undertaken to evaluate the concentrations of serum calcium and magnesium in obese adolescents and investigate their association with FBS and BP.

 

MATERIALS AND METHODS

Thirty apparently normal overweight (≥ 95^th percentile) and obese adolescents in the age group of 12-19 years (Cases) along with thirty normal weight (5th – 84^th percentile) ⁵ adolescents (controls) in the same age group were randomly selected for the study as per the inclusion and exclusion criteria.

Inclusion criteria

1. Apparently normal overweight and obese adolescents in the age group of 12-19 years served as cases.
2. Age and gender matched normal weight adolescents aged between 12- 19 years served as controls.
3. Subjects willing to participate and give consent for the same were included for the study.

Exclusion criteria

1. Overweight and obese adolescents suffering from diabetes mellitus, hypertension or any endocrine disorders or suffering from any syndromic cause of obesity.
2. Any history of taking medications by the subjects which is known to decrease the serum mineral concentrations like diuretics, amphotericin B etc was excluded.
3. Adolescents suffering from medical condition predisposing to mineral deficiencies such as gastroenteritis, chronic kidney disease, chronic liver disease or vitamin deficiencies were excluded.

Statistical analysis

Results on continuous measurements are presented as mean + SD (min-max) and results on categorical measurements are presented as %. Student’s t-test(two –tailed, independent) has been used to find the significance of study parameters on a continuous scale between two groups (intergroup analysis) on metric parameters. Levene’s test for homogeneity of variance has been performed to assess the homogeneity of variance. Chi –square/ Fisher exact test has been used to find the significance of study parameters on the categorical scale between two or more groups. Pearson correlation of serum calcium and magnesium with FBS were performed. The statistical software namely SAS 9.2, SPSS 15.0, Stata 10.1, Medcalc 9.0.1, Systat 12.0 and R environment ver.2.11.1(IBM, USA) were used for the analysis of the data. ^9-12

 

OBSERVATIONS AND RESULTS

Table 1 shows the comparison of anthropometric parameters in the two groups studied. From the table it is evident that the mean age of cases was 14.97+ 1.52 and that of controls was 15.70 + 1.49. The body weight (kg), waist circumference (in cm), and the BMI (kg/Sq.m) were significantly high in cases compared to controls.

Table 2 shows the comparison of PR, SBP (mm Hg) and DBP(mmHg) in the two groups. It can be observed from the table that PR, SBP, and DBP (mmHg) were significantly high in cases as compared to the controls; though all the parameters were within physiological limits in both groups.

Table 3 demonstrates the comparison of mean values of serum calcium, serum magnesium, and fasting blood glucose in the two groups. All the three parameters were statistically similar in both groups and were also within physiological range.

Table 4 illustrates the comparison of Pearson correlation between serum calcium, serum magnesium, and other parameters in the two groups studied. It appears from the table that a significantly negative correlation exists between serum calcium and BMI in both groups. Existence of this significantly negative correlation between serum calcium and BMI in overweight (and obese) adolescents is similar to the findings of Taheri. E et al..¹³

Significant negative correlation between serum calcium and PR seen in cases is similar to the observations of Lin LY et al.. ¹⁴

It appears from the table that a significantly negative correlation is present between serum calcium and SBP in cases. These observations are similar to those of Mu JJ et al.. ¹⁵

Apart from the above, a significantly negative correlation between serum calcium and fasting blood glucose can be observed in both groups. Observation of a significantly negative correlation between serum calcium and fasting blood glucose in overweight (and obese) adolescents is similar to the findings of Steinberger J et al.. ¹⁶

As can be observed from the table, in contrast to the above a significantly positive correlation has been found between serum magnesium and other parameters such as PR, SBP, and FBS in overweight (obese) adolescents. But no correlation was found between serum magnesium and BMI in both groups.

 

Table 1: Shows the comparison of anthropometric parameters in the two groups studied

 

 

Table 2: Shows the comparison of PR, SBP (mm Hg) and DBP(mmHg) in the two groups

 

Table 3: Demonstrates the comparison of mean values of serum calcium, serum magnesium, and fasting blood glucose in the two groups

 

Table 4: Illustrates the comparison of Pearson correlation between serum calcium, serum magnesium, and other parameters in the two groups studied

*Moderately significant (P=0.01<P≤0.05)

**Strongly significant (P≤0.01)

+suggestive significance (P=0.05<P<0.10)

 

DISCUSSION

A case control study with sample size of 60, was carried out in the department of physiology , VIMS, Ballari; to evaluate the selected serum mineral concentrations( calcium, magnesium) in overweight (and obese) as well as normal weight adolescents. Numerous studies have already been done to determine the association between the vitamin D status and insulin resistance in overweight and obese type 2 diabetic patients. Apart from this there are several studies showing the association between magnesium deficiency and insulin resistance in type 2 diabetic patients. However there are very few studies concerning the association between status of serum mineral concentrations and insulin resistance in apparently normal overweight and obese adolescents. Hence the present study was undertaken to evaluate the same. Anthropometric parameters such as weight (in kg), waist circumference (in cm), and BMI (kg/Sq.m) were significantly high in cases compared to controls. This is because cases and controls were selected randomly from the general population according to the inclusion and exclusion criteria laid down for the study. The present study reveals a significantly higher PR, SBP and DBP(in mm Hg) in cases compared to controls. This is because in overweight and obese adolescents, resistance to insulin has been known to be associated with chronic sodium retention and sodium sensitivity; that is reversible with weight loss and exercise. In addition to this obese insulin resistant adolescents are known to have an increased forearm vascular resistance which is reversible with weight loss.¹⁶ The serum concentrations of calcium, magnesium and fasting blood glucose were statistically similar in both groups and were within physiological range. A statistically significant negative correlation between serum calcium and other parameters like BMI (kg/Sq.m), PR, SBP(mm Hg), FBS(mg/dl) has been observed in cases. Obesity and fat accumulation is known to decrease the bioavailability of vitamin D and trap 25(OH)D in fat tissue.¹³ The association between dysregulation of the autonomic nervous system and metabolic syndrome has already been widely established. Especially sympathetic nervous system is known to play a central role in the development of metabolic syndrome.¹⁴ In obese adolescents, insulin resistance is known to be significantly associated with abnormal lipid profile and this explains a significant negative correlation between serum calcium and fasting blood glucose in them.¹⁶ The exact cause of existence of a significant negative correlation between serum calcium & BMI(Kg/Sq.m), FBS (mg/dL) in controls is not known. No correlation was found between serum magnesium and BMI in cases or controls. Unlike other studies, a significantly positive correlation has been observed in the present study between serum magnesium and PR, SBP(mm Hg), FBG cases. It is the intracellular magnesium which acts as a cofactor in over 300 enzymatic reactions. The serum magnesium concentrations may not appropriately indicate their intracellular levels.¹⁷ Hence the exact of this correlation is not known.

 

CONCLUSIONS

Serum concentrations of calcium, magnesium and fasting blood glucose were similar in over weight (obese) and normal weight adolescents of the same age group. A significantly negative correlation was found between serum calcium and other parameters i.e., BMI, PR, SBP, FBS in overweight (obese) adolescents. On the contrary, a significantly positive correlation was observed between serum magnesium and other parameters i.e., PR, SBP, FBS in overweight (obese) adolescents the cause of which is not known. Further studies are needed in this regard with large sample and with evaluation of ionic concentrations of these minerals.

 

LIMITATIONS OF THE STUDY

1. The present study was done with a small sample of 30 in each group.
2. Estimation of zinc , fasting insulin levels were not done.
3. Dietary assessment of intake of calcium, magnesium, vitamin D were not done.
4. Intracellular concentrations of the calcium and magnesium were not assessed.

 

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