Blood Pressure Distribution in Indian Children

Received: February 25, 2009;
Initial review: April 15, 2009;
Accepted: May 21, 2009.
Published online: 2009 September.

PII:S097475590900123-1
 

Objective: To determine blood pressure distribution in schoolchildren and to derive population specific reference values appropriate for age, gender and height status.

Design: Cross sectional observational study.

Setting: Schools in Ernakulam district, Kerala, India, during 2005-06.

Methods: Stratified random cluster sampling method was used to select the children. Blood pressure and anthropometric data were collected from 20,263 students of 5-16 years age. Three readings of blood pressures of each child were taken by mercury sphygmomanometer and mean was taken for analysis. Blood pressure percentiles in relation to gender, age and height were estimated from a non-overweight population of 18,931 children using polynomial regression models.

Results: Children from study population have higher diastolic pressures for both sexes than international standard across all age groups. For systolic blood pressure, girls showed higher values than the international standard while for boys, the difference appears to be minimal.

Conclusions: Blood pressure distribution in children from our study population demonstrates a different pattern in comparison to existing international reference. Higher blood pressure values in the study population are of considerable public health significance.

Key words: Adolescents, Blood pressure, India, Obesity, Overweight.

Hypertension in children is an emerging public health issue attracting the attention of medical professionals worldwide. Hypertension in children exhibits strong correlations with various factors, among which bodyweight assumes considerable significance(1-4). Excess weight resulting in hypertension in children deserves immediate attention even in large developing economies like India, China and Brazil(2,5,6). Data from diverse populations shows that the tracking of blood pressure from childhood into adulthood is very strong(7). In addition to aggravating cardiovascular morbidity and mortality burden, hypertension contributes significantly to other chronic diseases such as stroke and end-stage organ damage(8,9). Throughout adulthood, blood pressure is strongly and directly related to vascular as well as overall mortality(10).

A contiguous area with a population of approximately 1.37 million was selected from Ernakulam district, in central Kerala, India. Sampling was done by stratified random cluster sampling method. Schools in the area were stratified into 5 groups according to the strength of children and a representative sample of 46 schools with a cumulative population of 25,228 children was randomly chosen. Blood pressure (BP) and anthropometric data (height and weight) were collected from 20,263 students of 5-16 years age during the period 2005-06. Children with body mass index (BMI) more than or equal to 85th percentile of reference data were considered overweight(12). The reference data used to identify the cut offs were taken from CDC 2000 data set for BMI(13). A total of 18,931 non-overweight children were selected from the total sample and used for deriving blood pressure nomograms. Blood pressure was measured using mercury sphygmomanometer. Standard methodology, as recommended by the Fourth Report on the diagnosis, evaluation and treatment of high blood pressure in children and adolescents, was used to measure blood pressure(11). Three readings of blood pressures of each child were taken maintaining an interval of 2 minutes between the readings. Mean of the three readings was reported. Weight and height of each child were recorded using standard methods. The detailed design and methodology is available in our previous publication(2).

Table I 



Characteristics of the Study Sample

Figures in parentheses are standard deviations. 

BMI: Body mass index; SBP: Systolic blood pressure; 

DBP: Diastolic blood pressure.

The regression coefficients from polynomial regression model were derived for both genders separately. The intercept (a) for systolic BP was 100.63 in boys and 102.87 in girls. The corresponding values for diastolic BP was 66.25 and 67.35 respectively. The regression, co-efficients for various powers of age (b₁, b₂, b₃ and b₄) in case of systolic blood pressure for boys were 1.36, 0.17, 0.02 and –0.0036, respectively. The corresponding figures for girls were 2.66, 0.07, -0.03 and -0.0009. The values (b₁, b₂, b₃ and b₄) of diastolic blood pressure for boys were 1.21, –0.08, –0.00013 and 0.0019, respectively. The corresponding values for girls were 1.89, –0.06, –0.02 and 0.001, respectively. The regression co-efficients for various powers of height z score (g₁, g₂, g₃ and g₄) in case of systolic blood pressure for boys were 2.30, 0.02, –0.028 and –0.0098, respectively. The corresponding figures for girls were 1.36, -0.16, 0.015 and 0.016, respectively. The values (g₁, g₂, g₃ and g₄) of diastolic blood pressure for boys were 1.18, –0.13, 0.017 and 0.012, respectively. The corresponding values for girls were 0.89, –0.11, 0.007 and 0.012, respectively. The standard deviation (s) for systolic BP was 11.08 in boys and 11.6 in girls, and for diastolic BP was 9.07 in boys and 9.0 in girls.

TABLE II



Height Percentile Values in Centimeters for Boys and Girls

TABLE III



Blood Pressure (BP) Percentile Values for Non-overweight Boys in Relation to Age and Height Percentiles

Data constructed from the sample of non-overweight boys (N=9039).

TABLE IV



Blood Pressure (BP) Percentile Values for Non-overweight Girls in Relation to Age and Height Percentiles

Studies in the past have demonstrated that age appropriate blood pressure values tend to be more among boys than girls through out childhood and adolescence(11,15). The results of our study appear to be at variance to this finding. In our study, there is a relative increase in mean systolic and diastolic blood pressures in girls by the age of 9 years (Table I). By the age of 16 years, both genders have similar systolic blood pressure values. By the age of 16 years there appears to be minimal differences in diastolic blood pressure between both genders. Similar data was reported in a study from Jordan(16).

Early signs of a change in gender based blood pressure distribution among adolescents are emerging. Comparison of data sets from US adolescents demonstrated an increasing trend for high blood pressure among adolescent girls in contrast to a decreasing trend for the same in adolescent boys(17). The onset of sexual maturation is associated with increases in systolic and diastolic blood pressures(18,19). The timing of sexual maturity is different for boys and girls with the latter attaining it relatively earlier. This difference could contribute to differences in blood pressure progression during adolescence. The same reason could explain the lack of difference in systolic blood pressure and the comparable values in diastolic blood pressure between the genders by age 16, a time at which majority of the boys too have attained significant sexual maturity.

The blood pressure distribution pattern constructed using data from the present study was compared with an existing international refe-rence(14). There appears to be minimal difference in systolic blood pressure among boys from the two populations. There exists difference among girls in terms of systolic blood pressure with girls from the present study showing higher values consistently for all age groups (Fig.1). The difference in diastolic blood pressure appears to be more than the difference in systolic blood pressure. The same is consistently demonstrated in a higher magnitude in both gender and in all age groups, with children from the present study exhibiting higher values. In addition, the difference in diastolic blood pressure between the populations appears to be more in girls than boys. Higher values for mean systolic as well as diastolic blood pressures in comparison to US data were demonstrated previously for children from Indian, Jordan and Pakistan(16,20-22). All these studies have shown consistently higher diastolic blood pressures in comparison to US children. The differences in systolic blood pressures were less in magnitude compared to that of diastolic pressures. There appears to be a consistent difference in diastolic blood pressures between the present study and the US data(14), pointing towards a population-based difference. This difference appears to start even before the age of 5 years and persists into late adolescence. Similar trends in Pakistani and Jordanian children support this observation(16,22).

Fig. 1 Comparison of blood pressure between the present sample and US children. Comparison made for 50th percentile of blood pressure of non-overweight children at 50th percentile of height. Values derived from polynomial regression model. *Data with permission from ref 14.

22. Jafar TH, Islam M, Poulter N, Hatcher J, Schmid CH, Levey AS, et al. Children in South Asia have higher body mass-adjusted blood pressure levels than white children in the United States: a comparative study. Circulation 2005; 111: 1291-1297.