Association between waist-to-height ratio and elevated blood pressure in children: A cross-sectional study

INTRODUCTION

Hypertension in children is defined as blood pressure (BP) levels >95^th centile for <13 years and >130/80 mmHg for >13-year-old children, whereas the definition of elevated BP is BP levels ≥90^th centile to <95^th centile for <13 years and >120–129/80 mmHg for above 13-year-old age group and the prevalence is around 4% and 9%, respectively, children with BP >90^th centile exhibit a 2.4 fold greater risk for hypertension as adults and almost half of hypertensive adults had a BP >90^th centile as children.^[1] Early identification and management of raised BP are therefore essential.

BP in children is influenced by factors such as age, sex and body size.^[2,3] In particular, adverse BP patterns are more commonly observed in obese children and among certain ethnic groups.^[4] Obesity in children is associated with several metabolic and hormonal disturbances, including alterations in thyroid function. A mild elevation of serum thyrotropin, consistent with subclinical hypothyroidism, is commonly seen in children who are overweight or obese.^[5,6]

Body mass index (BMI) which is the most commonly used clinical parameter to comment on obesity has its limitations as it does not include central obesity which is a very important determinant of cardiovascular disorders. Waist circumference (WC), an important tool used to study central obesity, limits its use as it fails to have a single cutoff due to its variation across age, gender and ethnicity.^[7] Waist-to-height ratio (WHtR) has come into the picture as an alternative to central obesity which considers body size, allowing a single cutoff value across all ages and genders for both children and adults in various populations.^[8,9]

MATERIAL AND METHODS

In the current cross-sectional study, children of age group 6–17 years admitted to the paediatric ward of Employees’ State Insurance Corporation Medical College and Post Graduate Institute of Medical Science and Research, Rajajinagar, Bangalore, India were included after taking consent from the parents. Children diagnosed with chronic kidney and endocrine diseases, sick children requiring paediatric intensive care, parents not willing to consent, children with acute weight loss, children with moderate and severe dehydration and children on corticosteroids and immunosuppressants were excluded from the study.

After taking the approval of the Institutional Ethics Committee of Employees’ State Insurance Corporation Medical College and Post Graduate Institute of Medical Science and Research, Rajajinagar, Bangalore, India, the study was conducted with a sample size of 185 derived using a study conducted by Mishra et al.^[10] where the sample size was 1913, the prevalence of high WHtR was 14.1% (n= 270), using the formula –

Informed and written consent was obtained from the parents or legal guardians of all the participants before enrolment.

Height was measured using a portable stadiometer in the standing position at the end of deep inspiration. With both feet approximated and weight distributed evenly on both feet. The occiput, shoulder blades, buttocks and heels touch the flat surface of the stadiometer with arms hanging freely by the sides. The values were then approximated to the nearest 0.1 cm.

Weight was measured using a calibrated digital weighing scale in the standing position at the centre of the weighing scale with both feet approximated at an angle of 60° and the head in a neutral position with the tragus and eye in a straight line with the chin held horizontally; the findings were approximated to the nearest 0.1 kg.

WC was measured by a non-stretchable tape in the standing position, with the anatomical location being the midpoint between the lower border of the lowest rib and the upper border of the iliac crest in the horizontal plane with the tape being tight but not compressing the skin and parallel to the floor at the end of normal expiration. The values were approximated to the nearest 0.1 cm.^[11]

BP was measured by a digital sphygmomanometer in the right arm in the sitting position with a size-appropriate cuff after 5 min of rest. Two measurements were taken, and the average of the two readings was noted. BP levels >95^th centile for <13 years and >130/80 mmHg for >13-year-old children, whereas the definition of elevated BP is BP levels ≥90^th centile to <95^th centile for <13 years and >120–129/80 mmHg for the above 13-year-old age group.^[1] Age and sex-specific anthropometric percentiles were obtained using the Indian Academy of Paediatrics growth chart application. BP percentiles were interpreted using percentile charts derived from the fourth report on the diagnosis, evaluation and treatment of high BP in children and adolescents.^[2]

RESULTS

A total of 186 children participated in this study (100 were male - 53.8% and 86 were female - 46.2% with a mean age of 11.5 ± 3.7 with a range of 6–17. The prevalence of elevated BP was found to be 14.5%. 16.1% of the children were found to have WHtR of ≥0.5. Among children with high WHtR (≥0.5), 09 (30%) had elevated BP, compared to 21 (11.5%) among those with WHtR <0.5. The relative risk was found to be 2.6; 95% confidence interval 1.30–5.26; Chi-square 6.91; p = 0.0085 [Tables 1-3].

DISCUSSION

The prevalence of elevated BP was found to be 14.5% which is higher than the global prevalence of 9%^[1] and is comparable with studies conducted by Mishra et al.,^[10] Chen et al.,^[12] Tee et al.^[13] and Hu et al.,^[14] i.e. 10.7%, 8.8%, 19.1% and 10.7%, respectively. The relatively higher prevalence observed in our study may reflect increasing trends in childhood adiposity and lifestyle-related risk factors in urban Indian populations.

In the present study, a high WHtR was observed in 16.1% (n = 30) of participants. This finding is comparable to those reported by Mishra et al. [10] (14.1%), Chen et al.^[12] (31.2%) and Tee et al. [13] (18.5%), implying that central obesity is the culprit for elevated BP. In contrast, Jha et al.^[15] reported a lower prevalence of high WHtR (5%, n = 30), which is considerably low because of the large sample size and study done in semi-urban region where the prevalence of undernutrition (28.03%) is more than overweight/obesity [Table 4]. Figure 1 compares the prevalence of elevated blood pressure and high waist-to-height ratio across different studies.^[16]

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Figure 1: Prevalence of elevated blood pressure (BP) and high waist-to-height ratio (WHtR) across studies.

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There is evidence that impaired microvascular functioning caused by elevated obesity and central obesity indicators leads to hypertension.^[17,18] There is additional evidence that increased secretions of adipokines and cytokines in obese individuals alter the normal physiological processes leading to elevated BP.^[17] BMI, WC and WHtR are a few obesity indicators that can be used as an alternative for high BP screening as they require only simple anthropometric measurements, which are a part of routine school physical examination. WHtR can be easily assessed by well-trained staff with minimal educational qualifications.^[19]

The observed trend towards higher BP among children with central adiposity supports existing evidence that the WHtR may serve as a useful screening marker for cardiometabolic risk in the paediatric population.

CONCLUSION

Common clinical parameters such as BMI and WC do not have a single cut-off that can be used in all children. However, WHtR being only a screening tool, all children found to have a WHtR ≥0.5 must be referred to a physician for the diagnosis of hypertension.