The SA Journal Diabetes & Vascular Disease Volume 16 No 2 (November 2019)

SA JOURNAL OF DIABETES & VASCULAR DISEASE

RESEARCH ARTICLE

VOLUME 16 NUMBER 2 • NOVEMBER 2019

using the Omron (Hem 7120) automated blood pressure machine.

The mean of three recordings of systolic (SBP) and diastolic blood

pressure (DBP) and heart rate (HR) were computed. SBP and DBP

were converted to percentiles for age, gender and height for each

child, based on the Paediatric Task Force standards.

Both waist (WC) and hip circumference (HC) were measured

using the World Health Organisation guidelines.

Participating

children were requested to stand upright with feet together and

arms hanging freely at the sides. WC was measured at the smallest

circumference of the waistline with a non-stretch tape. Boys and

girls were requested to dress lightly on days of data collection. HC

was measured at the largest circumference around the greater

trochanter of the femur.

Height was measured using a stadiometer. Boys and girls were

requested to take off their shoes and to step on the stadiometer

platform with feet together and close to the stadiometer rod. The

movable bar was lowered to just touch the head. Height was read

off to the nearest cm.

Personal data such as height, age and gender were entered into

the Omron body composition monitor (BF511). Then each child was

requested to step onto the electrode pads of the body composition

monitor and hold the arm piece tightly in both hands, with arms

held out at right angles to the body, until the equipment stopped

scanning. The equipment displayed weight, body mass index (BMI)

and total fat mass (TFM). BMI was converted to percentiles for age

and gender.

Statistical analysis

Data were analysed using Stata version 14. Data were checked

for normality, and differences between the means of normally

distributed data were assessed using the

-test or ANOVA with

Dunnet’s test, while the Kruskal–Wallis test with Friedman’s post hoc

test was used for skewed data. Spearman’s correlation coefficient

(

) was used to determine the relationships between blood pressure

parameters and selected measures of adiposity.

Adiposity was categorised as lean with BMI < 85th percentile or

≤ 75th percentile for WC, HC or TFM for gender, and overweight/

obesity as BMI ≥ 85th percentile or > 75th percentile of WC, HC

and TFM for gender. Fisher’s exact test was used to determine the

relative risk for hypertension associated with overweight/obesity as

determined for the four selected measures of adiposity. Statistical

significance was set at

≤ 0.05.

Results

A total of 540 10- to 14-year-old boys and girls were recruited

into this study. Male and female participants were of similar ages.

Females had significantly (

< 0.05) higher BMI, WC, HC, TFM,

waist-to-height ratio (WHtR), SBP and DBP (Table 1). On the other

hand pulse pressure (PP) was similar for males and females.

The prevalence of overweight was 10.9% in the total cohort

and was higher in the girls (13.5%) compared to boys (8.0%). The

prevalence of obesity was 14.0% in the total cohort, 12.8% in the

boys and 15.2% in the girls (Table 2). Similarly, the prevalence of

pre-hypertension and hypertension were higher in girls compared

to boys.

In order to better understand the relationship between

blood pressure and measures of adiposity (BMI, WC, TFM,

WHtR), Spearman’s rank correlations were performed. Pairwise

correlations between SBP, DBP, PP, BMI, WC, TFM and WHtR

were positive in both boys and girls. BMI, WC, TFM and WHtR

correlated modestly with SBP and PP in females (Table 3). Only BMI

had a weak correlation with SBP and PP in males. On the other

hand there was no correlation between DBP and all measures of

adiposity in boys or girls.

In order to determine the effect of selected measures of

adiposity on blood pressure values, boys and girls were classified

according to their adiposity (BMI, WC, TFM, WHtR) quartiles. SBP,

DB and PP [PP = (SBP – DBP)] for each quartile were computed

and the prevalence of hypertension and pre-hypertension in each

quartile was determined. SBP, DBP and PP increased progressively

from the first quartile (lowest adiposity) to the fourth quartile

(highest adiposity). The prevalence of hypertension and pre-

hypertension were highest in the fourth quartile for all measures

of adiposity. The first quartiles for all measures of adiposity had

Table 1.

Characteristics of the learners by gender

Characteristics

Boys

Girls

Number

250

290

Age (years)

11.9 ± 0.6

11.9 ± 0.5

BMI (kg/m

)

18.9 ± 0.2

20.2 ± 0.3*

WC (cm)

65.4 ± 0.7

69.2 ± 0.7**

TFM (%)

22.5 ± 0.01

24.1 ± 0.01**

HC (cm)

80.1 ± 0.6

85.6 ± 0.7**

WHtR

0.44 ± 0.01

0.46 ± 0.00**

SBP (mm Hg)

110.1 ± 0.7

112.7 ± 0.6*

DBP (mm Hg)

70.6 ± 0.5

73.1 ± 0.4*

PP (mm Hg)

39.5 ± 0.5

39.5 ± 0.0.4

Calculated percentages were cohort specific.

BMI: body mass index, WC: waist circumference, TFM: total fat mass, HC:

hip circumference; WHtR: waist-to-height ratio, SBP: systolic blood pressure,

DBP: diastolic blood pressure, PP: pulse pressure. *

< 0.05, **

< 0.01.

Table 2.

Prevalence of overweight, obesity, pre-hypertension and

hypertension

Variables

Overweight Obesity Pre-hypertension Hypertension

Total cohort,

59 (10.9) 76 (14.0)

66 (12.2)

112 (20.7)

(%)

Boys,

(%)

20 (8.0)

32 (12.8)

28 (11.2)

39 (15.6)

Girls,

(%)

39 (13.5) 44 (15.2)

45 (15.5)

76 (26.2)

Table 3.

Spearman’s rank correlation coefficients between blood pres-

sure parameters and selected measures of adiposity

Spearman’s rank correlation coefficients

Variables

BMI (kg/m

) WC (cm)

TFM (%)

WHtR

SBP (mmHg)

Boys

0.24*

0.12

0.10

0.11

Girls

0.39*

0.37*

0.33*

0.27*

DBP (mmHg)

Boys

0.07

0.09

0.07

0.09

Girls

0.08

0.07

0.08

0.06

PP (mmHg)

Boys

0.22

0.05

Girls

0.41*

0.38*

0.35*

0.32*

BMI: body mass index, WC: waist circumference, TFM: total fat mass, WHtR:

waist-to-height ratio, SBP: systolic blood pressure; DBP: diastolic blood

pressure, PP: pulse pressure. *

< 0.05.