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RESEARCH ARTICLE
SA JOURNAL OF DIABETES & VASCULAR DISEASE
48
VOLUME 14 NUMBER 2 • DECEMBER 2017
and longer exposure to antiretroviral drugs, particularly protease
inhibitors. Only 10% of participants had a BMI > 30 kg/m
2
, 13 of
141 women and eight of 49 men had abdominal obesity (WC ≥ 80
cm in women and ≥ 94 cm in men).
The study design lacked comparator control groups (e.g. non-
HIV-infected individuals or HIV-infected persons pre-HAART),
making it difficult to determine the independent contribution of
antiretroviral therapy to the MetS and this limits generalisability of
the findings. However, it appears that obesity and the MetS were
substantially lower in HIV-infected individuals, despite the use of
different diagnostic criteria for the MetS.
Studies from other parts of sub-Saharan Africa have generated
wide variations in WC cut-off points. For example, central obesity
defined by WC > 102 cm in men and > 88 cm in women was more
common than generalised obesity (BMI > 30 kg/m
2
) in Cotonou,
Benin.
11
In South Africa, Motala et al.12 found that WC of > 86 cm
in men and > 92 cm in women predicted the presence of at least
two elements of the MetS in a cross-sectional, population-based
study in a rural setting. That study was heavily gender biased, with
80% of the 947 participants being female.
In 2014 Magalhães
et al.
,
13
in another cross-sectional study
of 615 university employees in Luanda, Angola, found overall
prevalence of overweight to be 47.8%, and obesity in 45.2%
of participants. Using JIS criteria, crude and age-standardised
prevalence of the MetS were 27.8 and 14.1%, respectively. The
crude and age-standardised prevalence of the MetS was 17.6 and
8.7% using ATP III criteria,
23
which apply higher WC cut-off points
(≥ 102 cm in men, ≥ 88 cm in women).
Applying ROC curves of WC to detect the MetS, new cut-
off points of this study were 87.5 cm in men (sensitivity 75.9%,
specificity 81.2%) and 80.5 cm in women (sensitivity 88.4%,
specificity 60.5%). The three most common criteria for the MetS
were increased WC, hypertension and low serum HDL cholesterol
levels. Women showed a higher prevalence in all age groups from
the age of 30 years.
The INTERHEART study, a case-controlled study of 27 000
participants from 52 countries, showed a graded and highly
significant association between waist:hip ratios (WHR) and acute
myocardial infarction worldwide.
15
The association of WHR with
acute myocardial infarction in the INTERHEART study addressed
one of the most fundamental cardiovascular sequelae of excessive
and disproportionate weight. Although the INTERHEART study
investigators cast doubt on the use of BMI in the context of acute
myocardial infarction, obesity, however defined, was associatedwith
a myriad of conditions, including hypertension, diabetes mellitus,
dyslipidaemia, obstructive sleep apnoea, gastro-oesophageal
reflux, sudden death, stroke, certain types of cancer, infertility,
degenerative joint disease and negative psychosocial impact.
The Prospective Studies Collaboration addressed the association
of BMI with cause-specific mortality in about 900 000 adults in
57 prospective studies.
24
These authors concluded that other
anthropometric measures such as WC and WHR could well add
extra information to BMI, and BMI to them, but that BMI is in itself
a strong predictor of overall mortality rate both above and below
the apparent optimum of about 22.5 to 25 kg/m
2
.
For screening purposes, it appears that measurements of WHR
provide no advantage over WC alone, are cumbersome and may be
fraught with errors in field situations. Furthermore, it may not be
necessary to measure WC in persons with BMI > 35 kg/m
2
since it
adds little value in the predictive power of disease-risk classification.
25
Inconsistencies in cut-off values for WC have potentially undesirable
consequences for cardiovascular risk stratification, disease
categorisation and prioritisation of preventative strategies for
obesity. There is therefore a strong need for validation of these WC
cut-off values for Botswana before they can be used for prediction
of incident outcomes such as cardiovascular diseases or type 2
diabetes mellitus.
Modelling may help to capture the scope and complexity of
the obesity problem in Botswana. Applications of heterogeneous
adaptive pieces of the puzzle that are affected by and/or influence
the overall behaviour of individuals within society may lead to the
development of empirically based public health models. Agent-
based modelling (ABM) represents one such simplified example.
26
Using the ABM approach, agents could represent individuals, their
attributes, behaviours and relationships with other individuals in
society. The environment could represent geographical locations,
mobility, domestic settings, market forces and social networking.
Systematic dynamic modelling (SDM) or perhaps more appro-
priately for Botswana, the MicroSimulation model, could be used to
establish temporal and causal associations, if any, between obesity
and related disorders, such as hypertension, diabetes, abnormal
lipids,cardiovasculardiseases,cancers,degenerativemusculoskeletal
disorders and psychological afflictions.
27
The strategy focuses on
‘upstream’ preventive approaches rather than ‘downstream’ acute
and chronic care. The goal is to enhance the number of safer,
healthier people and prevent others from becoming vulnerable or
being afflicted by obesity and its related complications.
There are, however, several limitations of this study worth
mentioning. Firstly, this was a retrospective analysis of case notes
of a small number of patients seen at a specialised private medical
practice. The finding may not therefore apply to the general
population. Secondly, WC reflects both subcutaneous and visceral
fat and at best represents a crude surrogate for visceral adiposity.
Because women generally have more subcutaneous fat, there is
a potential risk of misclassifying them as viscerally obese, thereby
resulting in overestimation of the MetS in women. Thirdly, little
is known about the full impact of the obesity epidemic on the
health of the community, and failure to demonstrate statistically
significant links between obesity and existing co-morbidities in this
study should not be construed to suggest benigness of obesity in
this population.
Conclusion
This study reiterates the need for ethnic-specific WC cut-off points
for defining central obesity and, by extension, for diagnosis of the
MetS among black Africans. The proposed WC cut-off values, if
validated, will set the pace for larger studies across sub-Saharan
Africa. Variations in WC cut-off values illustrate the uniqueness of
populations.
References
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(DAMCAB). MD thesis 2010, Makerere University, Kampala, Uganda.
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obesity among workers at Kanye Seventh Day Adventist Hospital, Botswana.
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Afr Med J
2009;
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2014;
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4. The World Factbook. Central Intelligence Agency. https://.cia.gov/ library/
publications/the-world-factbook/geos/bc.html. (Accessed 19 July 2015).