The relationship between body mass index and blood pressure: A study among school going children of Rajasthan, India

INTRODUCTION

Elevated blood pressure (BP) in children is considered as an important predecessor of adult hypertension.^[1] In a country like India, where double burden of malnutrition like under- and over-nutrition coexists, an emerging public health challenge is that of hypertension. The prevalence of hypertension among children ranges from around 5.4% to 19.4%.^[2] Existing literature suggests that hypertension could have its origin in childhood and a slight elevation in BP during childhood increases the risk of hypertension in adults several folds.^[3-5] During adolescence, there is an intense change in the life of every individual. This intense change can be of both psychological and physical nature. Psychological changes include intensification of emotional experiences, interest in and practice of adult social, economic, and sexual activities.

On the other hand, physical changes include growth spurt in height and weight, permanent tooth eruption, and development of secondary sexual characteristics.^[6] Moreover, it was found that BP varies with age and is closely related to height and weight of a child.^[7] Similarly, growth patterns and sex of an individual strongly influence BP levels among children and adolescents.^[8] There are some studies which have shown positive correlation between body mass index (BMI) and BP.^[9-11] In addition to this, various cross-sectional studies have reported that obese children have significantly high BP than those who are normal weight or underweight.^[12,13]

High BP either systolic or diastolic at any age is one of the risk factors for cardiovascular diseases.^[14] The previous studies have stated that systolic BP (SBP) elevation in childhood predicts arterial stiffness in young adults.^[15,16] On the other hand, diastolic BP (DBP) is important in monitoring BP in younger individuals.^[17] Earlier studies done among children and adolescents have shown high burden of hypertension in younger age groups as well.^[11,18] Moreover, significant increases in BP occur during adolescence period, and many temporary variations in BP level also occur before attaining more stable levels of adult life.^[7] However, such studies on adolescent obesity and hypertension in the rural Indian population are scarce. Thus, considering the importance of identifying the risk of elevated BP at an early stage of life, the present study aims to find out the prevalence of high BP among school going children belonging to the age group of 10–17 years. The study also examines the relationship between BMI and BP.

MATERIALS AND METHODS

A cross-sectional study was carried out among 240 boys belonging to Dangi community of Udaipur, Rajasthan. The sample size was calculated based on the prevalence of hypertension in children of Western India as 6.48%.^[19] The following formula given by Daniel, 1999, was used to calculate sample size.^[20]

Where, n = sample size, Z = Z statistic for a level of confidence (for the level of confidence of 95%, which is conventional, Z value is 1.96), P = expected prevalence or proportion (in proportion of one; if 6.48%, P = 0.06), and d = precision (in proportion of one; if 5%, d = 0.05).

n = (1.96)² × 0.06 (1–0.06)/(0.05)² = 87 (After substituting all the values).

To get more accurate and significant results, a sample size, that is, n = 240 was considered in the present study. An informed consent was obtained from the parents or the guardians of the participants. Children who were apparently healthy belonging to the age group of 10–17 years were included in the study. Children with any chronic or acute illness and those who were on long-term medications were excluded from the study.

General information such as educational level, occupation and income of the parents, family size, and dietary preference was collected using an interview schedule. Height was measured in centimeters (cm) using an anthropometric rod (Galaxy, India) and body weight was measured in kilograms (kg) using weighing scale (Krups, India). Both of these measurements were taken according to standardized protocols established by the International Society for the Advancement of Kinanthropometry.^[21] BMI was calculated as weight in kg divided by height in square meters (m²). The reference data used to identify the cutoff points were taken from the Centers for Disease Control and Prevention (CDC) 2000 dataset for BMI as per the guidelines of the Fourth Report on the Diagnosis, Evaluation, and Treatment of High BP in Children and Adolescents.^[3,22] Children who had BMI for age percentile <5^th were regarded as underweight, 5–<85^th percentile as of normal healthy weight, 85^th–<95^th as of overweight, and ≥95^th percentile as obese.^[22]

BP was measured in a sitting posture with the hands resting on the examining table with the cubital fossa supported at the level of the heart after providing a rest of 5–10 min.^[3] For each participant, it was measured thrice at an interval of 5 min each and mean of these three readings was used for statistical analysis. It was assured that each participant has not taken coffee, tea, water, or any kind of food item in last half an hour before measuring BP. Omron HEM-7080 digital BP monitor validated by Association for the Advancement of Medical Instrumentation and British Hypertension Society after calibration was used to measure BP using an appropriate size cuff.^[23] This study was approved by the Ethical Committee of the Department of Anthropology, University of Delhi, Delhi, India (Ref. No./2016/15).

RESULTS

The distribution of somatometric variables (weight, height, and BMI) showed a steady increase with age from 10 years onward to 17 years [Table 1]. The distribution of individuals into different categories of BMI revealed that 46% of the children had normal weight, 49% were underweight, 3% were overweight, and 2% were obese [Figure 1].

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Figure 1:

Distribution of body mass index categories among the studied population.

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The age-wise mean SBP, DBP, and percentile values were calculated from 50^th percentile to 95^th percentile [Table 2]. The mean values of SBP and DBP showed an overall increasing trend across age groups. Regression coefficients using polynomial regression models were obtained [Table 3].

The overall prevalence of hypertension (BP ≥95^th percentile) was found to be 16.2% among the studied population. It was found that 13 (5.4%) children had systolic hypertension, 14 (5.8%) diastolic hypertension, and 12 (5%) both systolic and diastolic hypertension [Table 4].

The distribution of individuals with different types of hypertension (systolic, diastolic, and both systolic and diastolic) was seen with respect to their BMI statuses [Table 5]. It was found that BMI was a significant determinant of hypertension. OR analysis revealed that children who were overweight/obese were more likely to have hypertension, whether systolic hypertension (OR - 2.39; CI - 0.43–13.0), diastolic hypertension (OR - 1.54; CI - 0.16–14.0), or both systolic and diastolic hypertension (OR - 1.34; CI - 0.14–12.1); however, the finding was not statistically significant (P > 0.05).

Moreover, it was found that among the children with normal weight, 8.2% had systolic hypertension, followed by both systolic and diastolic hypertension (7.2%), and diastolic hypertension (6.4%). Similarly, in case of overweight or obese children, 16.7% had systolic hypertension, followed by diastolic hypertension (8.3%), and both systolic and diastolic hypertension (8.3%) [Table 5].

DISCUSSION

The results of the study revealed that the majority of the population that is 49.16% falls under the underweight category. The prevalence of overweight/obese individuals is 5%. However, in the studied population, the overall prevalence of hypertension is found to be 16.2% (5.4% systolic hypertension, 5.8% diastolic hypertension, and 5% both systolic and diastolic). The prevalence of hypertension in our study is similar to that reported previously by Thangjam et al. in 2017. It showed 15.3% high prevalence of hypertension among the school going children aged 5–15 years of Manipur.^[18] Similar to this, another study from Imphal showed 15.7% prevalence of hypertension among students of higher secondary.^[24] In contrast to this, many other studies done in different regions showed the prevalence of hypertension in the school going children to be in the range of 3–10%.^{[11,19,25-28]} One of the study showed that the prevalence of hypertension among South Asian children was substantially greater than 5% predicted prevalence of high BP in children in the United States based on the same criteria despite of their lower BMI values.^[29] It is interesting to note that hypertension which is generally observed among overweight and obese individuals was also found among normal and underweight individuals of the present study.

Moreover, in the present study, it is found that children who are overweight/obese were nearly 2 times more likely to have hypertension compared to children who are having normal weight or underweight. Studies done in India and also in various other countries had similar findings to the present study.^[18,30-33] One of the studies done by Jena et al. proposed that greater BMI in adolescence is associated with elevated BP.^[13] Another study by Sorof and Daniels found that obese children are at a three-fold higher risk for developing hypertension than non-obese children.^[34] Similarly, Charan et al. found a significant rise of hypertension among obese participants whether boys or girls, thus, concluded that obesity plays an important role in development of hypertension during childhood.^[19] The reason behind this could be supported with the fact that in obesity, abnormal renal tubular dysfunction occurs in which tubular reabsorption of sodium is increased which, in turn, increases the extracellular fluid volume, blood volume, and thus, the BP. Another mechanism responsible for causing high BP in overweight and obese children is the activation of the sympathetic nervous system and reninangiotensinaldosterone system.^[35]

In review of the literature, there have been some studies that have shown that BP in children could be affected by various factors such as cultural, environmental, social, and genetic components, also the levels of BP varies with age, sex, and during growth and development period of an individual.^[36,37] One of the studies done among adolescents of New Delhi found lifestyle associated risk factors such as low physical activity, alcohol consumption, smoking, and inappropriate dietary practices (such as more fast food consumption and low fruit consumption) to be associated with high prevalence of obesity and hypertension.^[38]

CONCLUSION

The findings of the present study indicate that BMI is a crucial factor affecting BP levels. The study highlights the importance of screening children at younger age so that prevention of high BP can be done.