Introduction

India is undergoing an epidemiological transition where non-communicable diseases (NCDs) are on rise. According to World Health Report 2002, cardiovascular diseases (CVDs) will be the largest cause of death and disability by 2020 in India. ¹ The growing burden of CVDs is being contributed largely due to multitude of risk factors with hypertension being one of them.

Hypertension is one of the diseases which is diagnosed and treated in 25% of the cases only making it largely an under-diagnosed problem. ² There is plenty of evidence to suggest that hypertension begins in childhood and adolescence. ³ , ⁴ , ⁵ The asymptomatic nature of hypertension in early phases of its onset during adolescence increases the chances of developing complications during adulthood. ⁶ Therefore, detection of hypertension during childhood is of potential value in identifying those, who are at increased risk of primary hypertension as adults, and who might benefit from earlier intervention and follow-up. ⁷

Several studies in India have reported the prevalence of hypertension to be ranging between 0.46% and 11.7% amongst children and adolescents. ⁸ , ⁹ Further, a number of environmental factors have been found to be associated with hypertension in children and adolescents. ¹⁰ Thus, early detection of hypertension and its aggravating factors becomes imperative. The data on blood pressure (BP) profile of school adolescents is scanty in India. ¹⁰ , ¹¹ Considering the detection of hypertension in adolescence as the best possible preventive intervention to avoid complication later in life, the present study was undertaken to determine the prevalence of hypertension amongst urban school adolescents and its correlation with anthropometric measurements.

Methods

Study settings and participants

It was a cross-sectional study conducted in a public school in Central Delhi. The school authority and study subjects were explained the purpose of the study and assured privacy and confidentiality of the information provided by them. The assent from each student and informed consent from their respective parents were obtained, before taking detailed information and anthropometric measurements. The study was approved by institutional ethical committee. Based on the prevalence of hypertension as 10% amongst adolescents based on previous study ⁶ with 95% confidence interval and precision taken as 5%, sample size was calculated to be 142. ¹² However, all the 315 students of 9 ^thand 10 ^thstandard consented to participate and hence were included.

Study tools

Before the start of physical examination, students were briefed about the whole procedure. Any significant past history in last 1 year along with family history of NCDs like hypertension, diabetes and coronary heart disease, was asked from the participants and appropriately recorded.

Height and weight were measured for each student using validated techniques, ¹³ body mass index (BMI) was calculated and all the students were classified according to BMI for age scores as per Centers for Disease Control and Prevention (CDC) 2000. ¹⁴

BP measurements were also taken according to recommended guidelines. ¹⁵ For each subject, two recordings were taken at an interval of 30 min and the average of two readings was taken and it was considered to be the final reading. ⁶ Adolescents with BP levels at 120/80 mm Hg or above or average systolic blood pressure (SBP) or diastolic blood pressure (DBP) levels greater than equal to 90 ^thpercentile, but less than the 95 ^thpercentile, were classified as pre-hypertensive. The children were considered to be hypertensive if their SBP or DBP or both were equal to or more than the 95 ^thpercentile for age, sex and height. ¹⁵

Statistical analysis

The collected data was analyzed using Epi-info 2005 software and SPSS 16.0. Statistical analysis was performed using Chi-square test for categorical data and the Student t test for means where appropriate. P < 0.05 was considered to be significant. Possible interactions between the risk factors were also examined by calculating the correlation coefficients and their association with presence or absence of systolic and diastolic hypertension was quantified using univariate analysis. Variables with P ≥ 0.15 were included in multivariate binary logistic regression analysis to determine their independent contribution to development of hypertension.

Results

Out of the total 315 students, there were 208 (66%) boys and 107 (34%) girls. The mean age of the participants was 14.31 ± 0.96 years (range = 12-17 years). There were 37 adolescents (11.7%) (Boys = 26 (11.5%); Girls = 11 (10.3%); P = 0.45) who were classified as underweight while 25 (7.9%) (Boys = 17 (8.2%); Girls = 8 (7.5%); P = 0.69) were found to be at risk of overweight (Weight >85 ^thpercentile but <95 ^thpercentile) and 14 students (4.4%) (Boys = 12 (5.8%); Girls = 2 (1.9%); P = 0.09) were found to be overweight.

Overall the mean SBP was 108.38 ± 9.56 mm Hg and DBP was 72.38 ± 7.12 mm Hg Table 1.{Table 1}

The 5 ^thpercentile and 95 ^thpercentile of SBP for 13 years of age 90.4 mm Hg and 126.4 mm Hg respectively, and for DBP 60 mm Hg and 80 mm Hg respectively. At 16 years of age, the 5 ^thand 95 ^thpercentiles for SBP were 92.4 and 128.4 mm Hg and for DBP, it was 53.2 and 81.2 mm Hg respectively. Percentiles were not computed for age 12 and 17 as there were very few participants in these age groups Table 2.{Table 2}

There were only five students (1.6%) who were found to have systolic hypertension while 17 (5.4%) were having diastolic hypertension. While 4.1% ( n = 13) of the participants were found to be systolic pre-hypertensive, 26% ( n = 82) were in stage of diastolic pre-hypertension Table 3.{Table 3}

Variables such as younger age and BMI ≥23 were found to be significantly associated with diastolic hypertension while female gender and BMI ΃23 were found to be significantly associated with systolic hypertension Table 4. Putting the variables into logistic regression showed both gender (Odds ratio (OR) =8.01 (1.24-51.8); P = 0.028) and BMI (OR = 265.19 (20.73-3392.31); P < 0.001) to be an important predictor of SBP while only BMI (OR = 3.87 (1.30-11.2); P = 0.015) was found to be significantly associated with diastolic hypertension.{Table 4}

SBP showed positive correlation with BMI, age, height and weight (Pearson′s correlation coefficients: 0.29, 0.12, 0.40, 0.33, respectively) ( P < 0.05). DBP was also found to positively correlated with BMI, age, height and weight (Pearson′s correlation coefficients: 0.23, 0.04, 0.29, 0.185 respectively) ( P < 0.05 except for age).

Discussion

BP has been found to track from childhood with stronger tracking seen in older ages of childhood and in adolescence, to predict hypertension in adulthood. ¹⁶ In the current study, the prevalence of hypertension among the study group was found to be 7% ( n = 22). The finding is consistent with other studies reported from India. ¹⁷ , ¹⁸ The prevalence of pre-hypertension was 30.1% which is higher than reported by Sharma et al. ¹¹ in Simla in 2010 and surveys conducted in US. ¹⁹ The finding signifies an alarming situation as almost two in five children require some form of intervention as recommended by Fourth Task Force. ²⁰

Though, overwhelming evidence from observational studies suggests that SBP is more important prognostic determinant of CVDs end points than diastolic pressure, ²¹ this cannot be generalized for adolescents. In younger people, the predominant BP abnormality is a high DBP. ²² In the current study too DBP (5.4%) was found to be more common as compared to isolated systolic hypertension (1.6%).

The tendency of the BP to rise with age is supported by the findings from a Turkish study ²³ among the age group of 13-18 years and a study on Zambian school children (7-16 years). ²⁴ Both SBP and DBP also showed positive correlation with height and weight thereby re-affirming the relationship between body size and BP as shown in other studies. ²⁵

The association between elevated BP and BMI as noted in the present study, has also been reported by other authors from this part of the world. ⁶ , ¹⁰ , ¹¹ , ¹⁷ , ²⁵ , ²⁶ In the current study, both SBP and DBP were found to be significantly correlated with BMI. Present study results, obtained after multivariate analysis, strengthen the independent association of BMI with BP. Another interesting finding of the current study was the higher risk of girls developing systolic hypertension. This finding assumes particular importance as women are at greater risk of cardiovascular death than men for a particular age. ²⁷ Therefore, detecting and intervening at an earlier age hold the key to this public health problem.

The familial tendency to develop hypertension is well known. However, no significant association was found between the family history of NCDs and hypertension in adolescents. The possible reason could be the fact that we analyzed history of NCDs with hypertension in adolescents and not specifically the children with family history of hypertension.

Strengths and limitations of the study

The sample included in the study was from a single school of urban Delhi and therefore, may not reflect the true nature of the problem. Secondly, other factors such as salt intake, smoking, stress, physical activity and dietary habits also influence BP, but they have not been systematically studied in this study. However, application of validated methods for anthropometry and BP adds to strength of the study.

Conclusions

Limitations notwithstanding, the study does not defeat its purpose and gives a useful insight into the problem of hypertension particularly diastolic amongst the school adolescents. The study further deciphered some interesting findings such as association of gender with development of systolic hypertension not reported elsewhere from India. Thus, to conclude, it is evident that levels of hypertension and pre-hypertension were high among the school going children reflecting the changing scenario of CVDs in the current times. Further, pathogenesis of hypertension is being influenced by lifestyle factors such as BMI. Therefore, there is a need to institute regular screening of children and adolescents for BP so as to prevent them from developing cardiovascular complications later in life.