Association of BMI on Systolic and Diastolic Blood Pressure In Normal and Obese Children

Secondary data gathered from public health screening days at Child Health and Diseases Polyclinic of Kocaeli Metropolitan Municipality Maternity and Children Hospital on 1899 children. Each child was classified on the basis of ageand sex-specific Body Mass Index percentile (BMI%) as normal weight (BMI%< 85 th ), overweight (BMI%  85 th and < 95 th ), or obese (BMI%  95 th ). Systolic and diastolic blood pressures were compared among age-sex-BMI percentile groups.


Background
The worldwide increase of prevalence of obesity in childhood and adolescence poses an ever-increasing problem 1 as obesity is turning into a serious public health issue 2,3   .Many of the outcomes associated with obesity that was previously thought of as diseases of adults are now affecting children 4-6   .
The association between overweight and hypertension in children has been reported in a variety of ethnic and racial groups, with virtually all studies finding higher blood pressures and/or higher prevalences of hypertension in overweight children compared with normal children 7 .It is reported that obesity is one of the main effectors of BP in children 8, 9   .
There is a great deal of interest in defining and measuring adiposity and body composition among children and general consensus is that an age-related BMI should be used, since it is significantly associated with body fatness in children and adolescents 10, 11   .Definition of childhood overweight/obesity should aim to identify children with excess body fat in order to treat the associated adverse health outcomes.At the population level, this should help identify children at higher risk of developing the adverse consequences of obesity in order to implement early preventive strategies against disease.Whilst clear-cut definitions of overweight and obesity are available for the adult population, child growth adds a dynamic component that complicates the definition of these conditions 12 .
Overweight and obesity were defined according to the recommendations of the International Obesity Task Force, IOTF, using international reference values based on data from six countries.These age and sex specific BMI cut-off points for overweight and obesity in children (between 2 and 18 years) were constructed using dataset specific centiles corresponding to the widely accepted adult cutpoints of a BMI of 25 kg/m2 (overweight) and 30 kg/m2 (obesity) The purpose of this study is to investigate whether an association between normal, overweight and obesity BMI and blood pressure values could be detected in children in the paediatric primary care practice as childhood BP is together with the changes in the BMI is a predictor of adult blood pressure 4,16   .The emphasis is to determine whether a relationship could be formed for young children as well as in children within the normal BMI% group.

Materials and Methods
This study has been carried out on secondary data gathered from children between the ages of 6 and 14 years seen during weekly public screening days at Kocaeli Metropolitan Municipality Maternity and Children Hospital in Kocaeli, Turkey during the year 2002.
During the public screening, history of every child was taken by doctors.Children who already suffered major disorders (cardiac, respiratory, renal or haematological disorders) were not considered in this study.The medical examination of the children was carried out by a doctor in a quiet, comfortable and warm polyclinic room.
Heights and weights of children with shoes off and least possible clothes were measured.Measurements taken were the children's height in centimeters (cm) and weight in kilograms (kg).Height was measured with a stadiometer in centimetres (cm) attached to the wall.
Children were rested for fifteen minutes before their blood pressure measurements.Blood pressure was measured with the child in a seated position according to paediatric measurement guidelines 17 by auscultation with an appropriate-size cuff and an aneroid sphygmomanometer.The fifth Korotkoff sound was used to determine diastolic blood pressure.Three blood pressure measurements were taken with three minutes intervals and the average value of these three measurements was recorded.Blood pressure, height and weight were always measured by the same doctor to ensure uniformity of recording.Children were compared with respect to BMI and BMI%.
The systolic blood pressure (SBP) and diastolic blood pressure (DBP) values of the children in each BMI% groups were also compared with BMI values in the other groups.In addition, the correlation of SBP and DBP with BMI was evaluated in all BMI% groups including normal BMI% group, adjusted for age.
Statistical evaluation of the results was performed with the SPSS14 computer program using simple multiple linear regression.All significance tests were based at the 0.05 level of significance.

Results
One thousand and eighth hundred ninety nine (1899) children (male/female ratio=1033/866) with a mean age 9.522.62years were enrolled in the present study.Normal, overweight and obese BMI% were called group 1, 2 and 3 respectively and this notation will be adopted in the rest of this paper.The mean and standard deviation of systolic and diastolic blood pressure values in each BMI% group and BMI were also calculated and compared.SBP and DBP have shown a graded, statistically significant increase from normal weight to obese children.After adjustment for age, BMI, normal, overweight, obese BMI% SBP and DBP differences remained statistically significant at P < 0.05.
BP is increasing with increasing BMI in all age groups and this could be detected in young children.Fig. 1a and Fig. 1b show mean DBP and SBP values with respect to age.It can be seen that BP is increasing with increasing BMI values even in normal group but the increase is more in obese children.Burke et al. 18 recently described an independent association between high BP and IOTF-defined overweight and obesity, in a prospective study carried out in an Australian cohort of children followed-up from the age of 9 to 25 year old, as did Genovesi et al. 19 in a cross-sectional study carried out in a sample of school children living in northern Italy.It is reported in the study of Sorof et al. 5 that, among all demographic and clinical factors analyzed, BMI was most strongly associated with hypertension.Mirza et al 20 found that mean SBP was significantly higher in overweight children.
Our results show that the mean difference of both SBP and DBP between the matched BMI was found to be significant (P<0.05) in early life.Moreover, there is an impact of childhood BMI on BP in the normal BMI% group children.An increase in adjusted BMI and BMI% can then be associated with an increase in SBP and DBP in children.
In addition, our data has shown that there is a significant association between BMI and BP in all age groups (6-14 years old) even in young children.Compared with children with BMI % < 85 th , both SBP and DBP values are higher in children with BMI% 85th and <95th and were highest in children with BMI% 95th in 6-14 years.Falkner et al. 8 have reported the same trend in all age groups they considered.Reinerh et al 1 reported that children older than 12 years had a slightly increased risk of hypertension probably reflecting the influence of duration of obesity.
Furthermore, it can be seen that BMI is also increasing for normal children.This important finding was also reported in the study of He et al. and raises the question of how to define childhood obesity should it be based on a functional outcome such as BP or on a statistical cut-off point of a population-based BMI distribution as stated in the study of He et al.

Conclusion
Our results show that BMI is associated with elevated SBP and DBP in overweight and obese children.BP is increasing with increasing BMI values even in normal group but the increase is more in obese children.This is an important and interesting finding and was reported in the literature once before.These results also suggest that careful monitoring of age related normal growth increase in the BMI in childhood and tackling and keeping it within the normal limits is important in preventing higher BP values and related health problems later in life.

Table 1 : Mean age, weight, height, BMI, SBP, DBP and M/F of BMI% groups (normal, overweight and obese).
The number of children, male/female ratio, mean age, weight and height, BMI, SBP and DBP of each group are shown in Table1.It shows that BMI, SBP and DBP have increased from normal to obese group and mean age in each BMI% groups are similar.