The SA Journal Diabetes & Vascular Disease Volume 17 No 1 (July 2020)

RESEARCH ARTICLE

SA JOURNAL OF DIABETES & VASCULAR DISEASE

VOLUME 17 NUMBER 1 • JULY 2020

the only senior secondary school in the Okavango, a sub-district

with a population of 2 529 inhabitants, mostly subsistent farmers

and pastoralists.

St Joseph’s College is located in Gaborone, the

capital city, with a population of 231 592.

The two schools were conveniently selected based on their ease

of accessibility and to provide widely different populations. There

were 36 and 42 classes at St Joseph’s College and Shakawe senior

secondary school, respectively. Four classes were selected from

each school using a simple random-sampling technique.

All students in the selected classes were invited to participate in

the study and were provided with a written description of the study,

and informed consent forms to take to their parents/guardians

(written in both English and Setswana). If willing to allow their

child to participate, parents/guardians were then asked to sign the

consent form. Students agreeing to participate signed assent forms.

Ethical approval for this study was obtained from the Ministry

of Health institutional review board [HPDME: 13/18/1 Vol. X (152)].

Permits were obtained from the Ministry of Education and Skills

Development, local authorities in Okavango and Gaborone and

from each school administration.

Information on date of birth, gender, alcohol intake and

tobacco use, and the level of physical activity was obtained using

self-administered questionnaires. Personal and family history of

heart disease, hypertension, kidney disease, diabetes mellitus,

dyslipidaemia and stroke were also documented. Height was

measured in all participants without footwear to the nearest 0.1 cm

using a stadiometer. Weight was measured using a digital scale to

the nearest 0.1 kg in light clothing and without footwear.

We used WHO AnthroPlus version 1.0.4 software to calculate

body mass index (BMI) for all participants aged below 18 years.

BMI z-scores according to age, gender and height were recorded

for each participant and designated as underweight [z-score < –2

standard deviations (SD)]; normal weight (z-score –2 SD – +1 SD);

overweight (z-score +1 SD – +2 SD); and obese (z-score > +2 SD).

For participants ≥ 18 years, adult BMI reference values were used

for underweight (≤ 18.5 kg/m

), normal weight (18.5–24.9 kg/m

overweight (25–30 kg/m

) and obesity (≥ 30 kg/m

Waist circumference (WC) was measured to the nearest

centimetre in light clothing at the level of the umbilicus using a

non-distensible measuring tape. Using the Canadian percentile

charts for WC based on gender and age, WC > 90th percentile was

categorised as overweight for students < 18 years.

For students ≥

18 years, adult cut-offs of 94 cm and 80 cm were used for males

for females, respectively.

After five minutes of rest, two seated blood pressure (BP)

measurements were taken from the participants’ right arms using

portable sphygmomanometers (BPCB0A–2H, China). The second

measurement was taken after a five-minute interval and the average

of the two BP readings was recorded. An average systolic blood

pressure (SBP) or diastolic blood pressure (DBP) ≥ 95th percentile

for age, gender and height was used to define hypertension. Pre-

hypertension was defined as SBP and/or DBP ≥ 90th percentile but

< 95th percentile.

A repeat blood pressure measurement was done after one

week for participants whose readings were consistent with pre-

hypertension and hypertension during the initial measurement.

Participants whose average SBP and/or DBP remained high in the

second visit were categorised as hypertensive and pre-hypertensive

as appropriate.

25,26

We also defined hypertension among participants

who self-reported current antihypertensive medication use.

Fasting blood glucose (FBG) level was measured in mmol/l

on capillary blood from a finger-prick test using the Accucheck

Performa system (Roche Diagnostics, Mannheim, Germany)

following a minimum fasting period of eight hours in participants

not known to have diabetes mellitus. Using the American Diabetes

Association diagnostic criteria, participants were classified as having

normal fasting glucose levels (< 5.6 mmol/l), impaired fasting

glucose (5.6–6.9 mmol/l) or diabetes mellitus (≥ 7.0 mmol/l).

Alcohol use was defined as any reported alcohol consumption

in the previous year, while cigarette smokers were current smokers.

We assessed self-reported physical exercise duration and intensity

in the previous week (both at school and during leisure time)

to three levels of physical activity: inactive, minimally active and

health-enhancing physical activity.

Statistical analysis

The prevalence of hypertension and selected risk factors among

adolescents is unknown in Botswana. Consequently, the sample

size was calculated from the assumption that the prevalence of

hypertension in Botswana was 20%, similar to that found in

South Africa.

We needed 250 participants to determine the true

prevalence of hypertension with a margin of error of ± 5%.

Data were entered and analysed using SPSS for Windows,

version 23.0 (IBM Corporation). Continuous variables (fasting blood

glucose, height, weight, WC, SBP, DBP and age) were summarised

by means (± SD). Counts and percentages summarised categorical

variables. A Pearson’s chi-squared test was used to compare the

prevalence of selected cardiovascular risk factors (hypertension,

diabetes mellitus, smoking, obesity/overweight, level of physical

activity and alcohol use) between urban and rural students.

For univariate analysis of continuous variables (fasting blood

glucose, height, weight, WC, age), the Student’s

-test was used.

-value less than 0.05 was considered statistically significant.

Variables that were variables with

< 0.25 in the univariate analysis

were included as independent variables for the multivariable logistic

regression.

Results

A total of 252 students (132 from Shakawe senior secondary

school and 120 from St Joseph’s College) participated in the study

(Table 1). Of these, 172 (68.3%) were females, and the mean (SD)

age was 17.1 (0.9) years. Students from the rural school were older

than those from the urban school (17.5 vs 16.7 years;

< 0.001).

None of the participants had a history of diabetes mellitus, stroke

or dyslipidaemia.

Overall, obesity or overweight was observed in 10.3%of students

(12.5% in the urban school and 8.3% in the rural school). Female

students were more likely to be overweight or obese than male

students (Table 2). Underweight was found in 25 (9.9%) students,

and was more prevalent in male than in female students. There

were no urban–rural differences in the prevalence of underweight.

None of the study participants had diabetes mellitus. Impaired

fasting glucose was found in 1.6% of participants (all females), 1.7

and 1.5% among urban and rural school participants, respectively.

Twenty-three (9.1%) participants reported drinking alcohol.

Urban students were more likely to drink alcohol than rural students

(14.2 vs 4.5%;

= 0.008). Smoking was rare in both schools.

However, male students were more likely to report cigarette

smoking than female students (0.6 vs 5%;

= 0.019).