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SA JOURNAL OF DIABETES & VASCULAR DISEASE
RESEARCH ARTICLE
VOLUME 14 NUMBER 2 • DECEMBER 2017
45
the subject’s abdomen, mid-way between the rib cage and the iliac
crest, and standard tension was applied.
Demographic data, anthropometric measurements and co-
morbidities for individual patients were entered into a database
created using the Statistical Package for Social Sciences (IBM SPSS
statistics 20
®
). Correlation plots were made for BMI (kg/m
2
) and WC
(cm) in men and women, using 30 kg/m
2
as the reference cut-off
point for obesity, to determine corresponding mean WC (+ 95%
CI) in both genders. Similar plots were made for BMI and WC using
94 cm in men and 80 cm in women as reference cut-off points
for obesity to determine corresponding BMI (+ 95% CI) in both
genders. Height (m) was also plotted against WC in both men and
women.
Patients were grouped into five WHOweight categories:
16
normal
weight (category 1; BMI 18.5–24.9 kg/m
2
), overweight (category
2; BMI 25.1–29.9 kg/m
2
), grade I obesity (category 3; BMI 30.0–
34.9 kg/m
2
), grade II obesity (category 4; BMI 35.0–39.9 kg/m
2
),
and grade III obesity (category 5; BMI ≥ 40.0 kg/m
2
). Women were
arbitrarily grouped into three WC categories: category 1 (WC ≤ 80
cm), category 2 (WC 80.0–87.9 cm) and category 3 (WC ≥ 88 cm).
Men were likewise grouped into three WC categories: category 1
(WC ≤ 94 cm), category 2 (WC 94.0–101.9 cm) and category 3
(WC ≥ 102 cm).
Statistical analyses
With MedCalc
®
software,
17
using category 1 BMI and category
1 WC as references, relative risks (+ 95% CI) for hypertension,
dysglycaemia and dyslipidaemia were calculated for different BMI
and WC categories. Sample means and standard deviations were
calculated in the conventional way. Level of statistical significance
was taken to be
p
< 0.05.
Results
A total of 498 case notes were retrieved; 23 did not contain the
required data. Of 475 case notes of patients with the required
anthropometric parameters, 20 naturalised non-black citizens
of Botswana, 25 Asians and 12 Caucasians were excluded; the
remaining 418 black African patients were analysed. This consisted
of 215 men (51.4%) and 203 women (48.6%), mean age 50.0 ±
10.8 years, 80.6% of whom were Batswana and 19.4% were other
black Africans.
Only 7.2% had normal weight (BMI 18.5–24.9 kg/m
2
), 27.3%
were overweight (BMI 25–29.9 kg/m
2
) and 65.5% were obese
(BMI > 30 kg/m
2
). Significantly more women were obese (77.8%)
compared to men (54.0%); mean BMI was 34.9 ± 6.5 versus 31.0
± 4.9 kg/m
2
(
p
< 0.0001). Hypertension affected 77.8% (325/418)
and dysglycaemia 44.3% (185/418) of the patients. Lipid profiles
were not estimated in a third of the sample group. Dyslipidaemia
was documented in 67% of the remaining 279 patients.
One man did not have a WC measurement and was excluded
from the correlation plots. WC directly correlated with BMI in both
genders (R2 linear = 0.774 in men; 0.644 in women) with new
cut-off points of 98 cm (95% CI: 96.9–98.2 cm) in men and 85
cm (95% CI: 83.0–86.5 cm) in women, corresponding to BMI of
30 kg/m
2
. (Fig. 1A, B). The current operational WC of 94.0 cm in
black African men corresponded to a BMI of 28.7 kg/m
2
, whereas
in black women, the corresponding BMI was 28.0 kg/m
2
for a WC
of 80 cm (Fig. 2A, B).
In both men and women, there was a poor correlation between
height and WC (
R
2
linear = 0.036 in men; 0.005 in women)
(Fig. 3A, 2B). There was no correlation between age and BMI
among the 418 patients (
R
2
linear = 0.001).
Table 1 shows the relative risks of hypertension, dysglycaemia
and dyslipidaemia for different BMI categories versus normal weight
(BMI < 25 kg/m
2
) among 418 patients. Table 2 shows the relative
risks of any cardiovascular disease for different WC categories
versus current reference WC (< 80 cm in women; < 94 cm in men).
Both tables demonstrate no overall statistically significant risk
relationship with hypertension, dysglycaemia and dyslipidaemia.
Separate analysis showed that WC ≥ 102 cm in men was associated
with 21% increased total co-morbidity, combining cardiometabolic
and musculoskeletal disorders (RR 1.21; 95% CI: 1.03–1.42;
p
=
0.022).
Figure 1.
Correlation between BMI (kg/m
2
) and WC (cm) in (A) 214 men and (B) 203 women with BMI = 30 kg/m
2
as cut-off point. BMI, body mass index; WC, waist
circumference.
A
B