CARDIOVASCULAR JOURNAL OF AFRICA • Volume 25, No 1, January/February 2014
AFRICA
31
Worldwide, the metabolic syndrome is increasingly
becoming a pandemic,
7
the level of prevalence being estimated
to be 17–25% in the general population. However, estimates in
sub-Saharan African populations are scarce and inaccurate.
11
The
crude prevalence in this study was in an intermediate point of
the range (0–50%) reported for different African populations.
11
The three most frequent components of the metabolic
syndrome were elevated blood pressure, low HDL-C levels and
elevated WC. A similar cluster of components was reported in
an urban population in Kenya,
20
and in a study including West
Africans (Nigeria and Ghana) and African-Americans.
34
Other
studies reported a combination of high WC and low HDL-C
levels as the most frequent components in Africans with high a
prevalence of the metabolic syndrome.
14,18,25
Although the underlying mechanisms are not fully understood,
the increasing prevalence of the metabolic syndrome has been
associated with a sedentary lifestyle and obesity.
7
Also, it has
been reported that in contrast to developed nations, in some
African nations, a higher socio-economic status has been
associated positively with increased obesity.
35
In our study, distribution of the metabolic syndrome according
to socio-economic class, defined by average household monthly
income, was not significant. However, this study also showed
a high prevalence of both obesity and overweight (47.8%) and
hypertension (45.2%). The three most common components
of the metabolic syndrome were elevated blood pressure, low
HDL-C levels and high WC, suggesting a high risk for CV
diseases in this occupational cohort. Therefore, considering the
on-going socio-economic changes in Angola, the findings of
this study may reflect the impact of the nutritional transition,
behavioural and occupational changes, environmental risk factors
and unhealthy lifestyle (mainly sedentary) with rapid weight
gain, and the high consumption of salty and high caloric food.
Although this study showed a good concordance between
the two criteria, the crude prevalence estimated with the JIS
definition was 10.2% higher than that estimated with ATP III.
This difference was mainly attributed to the different cut-off
point for WC, which is lower for JIS than for ATP III criteria.
It is known that WC reflects both visceral and subcutaneous
fat depots, but it has been used as a crude but relevant index
of visceral adiposity. The role of visceral adiposity in the
development of each metabolic syndrome component has been
shown in non-African populations.
36-39
In sub-Saharan African
populations, a high WC was suggested as a key determinant for
development of the metabolic syndrome.
14
However, since country-specific cut-off values of WC still
need to be defined for Africans, the cut-off values of WC derived
from European population groups have been recommended
for Africans.
5,7
Emerging data suggested that African-specific
cut-off values would be different from European cut-off values
currently recommended by the IDF.
18,24,25
In this study, the cut-off
values for men were lower than that currently recommended for
Africans (87.5 instead of 94 cm);
5,7
whereas for women, these
cut-off values were similar to those recommended for European
and African women (80.5 vs 80 cm).
A few studies have attempted to establish cut-off values of
WC for African groups,
18,24,25
and they found different cut-off
values from those currently recommended. In our study, the
value of 87.5 cm for men is similar to that reported in South
African studies of African men (86 cm),
18
but different for
women.
18,25
However, our findings differed from those reported
for men and women in another study of the same population
(men: 90 cm, women: 98 cm).
24
Discordant cut-off values of WC between different studies
are to be expected since even in the same ethnic group, the WC
may vary according to the country, as emphasised by the IDF
5
and the JIS.
7
Furthermore, it has been reported that variation in
WC cut-off values obtained using the sensitivity and specificity
approach were strongly correlated with mean levels of WC in
the population.
40,41
The cut-off values increased linearly with
increasing population means, independent of WC measurement
techniques and regardless of whether the health outcome was
hypertension, dyslipidaemia, hyperglycaemia or a cluster of
multiple outcomes.
40
However, it remains to be clarified whether
this variation was due to biological characteristics or the
methodological approaches used to define the best cut-off point.
40
In this study, women had higher mean values of WC than
men (Table 1). It is known that the proportion of total fat in
subcutaneous depots is higher in women than men.
42
Therefore
there is a potential risk of misclassification of women as having
excessive visceral adiposity by using values of WC to predict
other components of the metabolic syndrome. To minimise this
difficulty in this study and ensure a correct classification for only
women with strong evidence of two or more components of the
metabolic syndrome, we selected the best cut-off values of WC,
as suggested by the higher values of theYouden index. Therefore,
this study reinforces the opinion that definition of cut-off values
of WC should be country- and gender-specific.
There was a potential limitation to this study. Because we
studied a convenient sample consisting of staff of a public
university, our findings may not apply to the Angolan population
as a whole. As previously detailed,
27
however, participants
were recruited from all higher education institutions, which
represented university staff in the whole country. When this
study was designed in 2009, all university staff were invited
to take part. The study group included all occupational and
socio-economic classes, including teachers and non-teaching
workers.
26,27
Conclusion
There was a high prevalence of the metabolic syndrome in this
occupational cohort, with a higher prevalence among women.
This study suggested that optimal cut-off values of WC of
87.5 and 80.5 cm would be appropriate for the diagnosis of the
metabolic syndrome in men and women, respectively. This may
imply that the prevalence would have been different from that
reported in this study if these values had been used. Further
investigation is therefore needed to confirm optimal cut-off
values of WC in the general Angolan population, in order to
consistently estimate the trends of cardiometabolic risk factors
in African populations.
This study was supported by grants from Fundação para Ciência e
Desenvolvimento, Angola and CAPES, Brazil.
References
1.
Lakka HM, Laaksonen DE, Lakka TA, Niskanen LK, Kumpusalo E,
Tuomilehto J,
et al.
The metabolic syndrome and total and cardiovas-
