CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 7, August 2012
AFRICA
393
CRP and high TC, LDL-C or TG levels.
Overall, 43 patients (2.2% of cohort with LDL-C levels
measured) recorded an LDL-C
≥
4.9 mmol/l, and 32 patients
(1.8% with TC levels measured) had TC
≥
7.5 mmol/l. A total
of 56 patients (2.6%), comprising 43 of African descent (2.4%
of ethnic group), six white Europeans (4.2%), three of mixed
ancestry (3.4%) and four Indians (3.0%) had either elevated
LDL-C or TC levels, suggestive of FH.
Discussion
This study provides important insights into the lipid profiles
according to ethnicity of more than 2 000
de novo
cases of heart
disease in Soweto, South Africa. We found significant gradients
in lipid levels on this basis. Patients of African descent had the
lowest, and Indians the highest TC, LDL-C and TG levels. These
gradients in TC and LDL-C levels were particularly distinct
in their magnitude and may represent clinically important
differences for the development of atherosclerosis (see below).
However, HDL-C levels did not differ across ethnic groups.
Therefore the assumed protective role of HDL-C in the African
population was not evident beyond cases of CAD (where African
patients were under-represented).
Overall, there were important differences in the risk factor
and clinical profile of cases according to ethnicity. Irrespective
of the relatively low levels of TC, low HDL-C was widespread,
affecting nearly two-thirds (63%) of this cohort. This was
surprising when considering the proportion affected with high
TC (43%), LDL-C (47%) and TG (27%) levels. As a strong,
independent predictor of CVD,
16
this phenomenon of low HDL-C
levels represents a potentially important therapeutic target for
truncating an increasing burden of atherosclerotic disease in
urban, sub-Saharan African communities. It is possible that
an acute-phase response could lower HDL-C levels in most
instances and may account for the reciprocal relationship found
between CRP and HDL-C.
Our observations in respect of ethnic differentials in lipid
profiles are broadly consistent with prior studies in the region.
9,17-20
Previous research has shown that those of African descent
display an athero-protective lipid profile compared to white
Europeans and Indians.
5
Similarly, the INTERHEART Africa
case–control study (which investigated risk factors associated
with first-time myocardial infarction) showed no difference in
HDL-C levels between those of African descent, mixed-ancestry
and European/other African groups.
18
However, fewer than 200
cases were of African descent.
Norman and colleagues reported in 2000 that cholesterol-
attributable mortality rates were highest in the Indian population
of South Africa (at 22.2%), followed by white European (20.5%)
and mixed-ancestry (8.8%) populations.
9
By comparison,
mortality attributable to ‘sub-optimal’ lipid levels (defined as
TC
≥
3.8 mmol/l) in those of African descent was only 1.8%,
which reflected low TC levels compared to other ethnicities.
9
Nonetheless, varied reports show that dramatic increases in mean
TC levels have occurred in the past four decades,
19,20
while HDL-C
levels have decreased,
21,22
both of which may be contributing to
the increase in CAD prevalence over a similar time period.
2
It is
likely that the continued influences of epidemiological transition
(giving rise to extensive urbanisation, Western diet and sedentary
lifestyle) will continue to fuel these patterns.
23
The prevalence of FH in African populations is unknown
but is probably about 1:500, as has been reported in most
other populations studied worldwide. South Africa has several
communities in which there are founder effects that increase
the prevalence of FH, including the Afrikaner, Jewish and
Indian communities. Several LDL-C receptor errors have been
identified in patients of mixed ancestry.
24
In this cohort, genetic
disorders such as FH were unlikely to be a major contributor
to
de novo
presentations of heart disease, given the small
number of probable/possible cases of the same (2.3%). Mixed
hyperlipidaemia that could relate to an uncommon mutation in
apoE in those of African descent was also not suspected.
Examining the potential impact of migration on CVD and its
risk factors may be helpful in understanding ethnic differences in
the relative incidence of CVD in different African populations.
25
In our multivariate analyses, urban (Soweto) origin was not
associated with high TC or LDL-C, or low HDL-C levels. This
was similar to a study on adults of the Cape Peninsula,
26
in
which measures of urbanisation had no effect on TC levels
per
se
; rather, it was clusters of risk factors that corresponded with
increased time residing in an urban setting.
TABLE 2. INDEPENDENT CORRELATES OF HIGH SERUMTOTAL CHOLESTEROL,
HIGH LOW-DENSITY LIPOPROTEINAND LOW HIGH-DENSITY LIPOPROTEIN CHOLESTEROL
High TC
High LDL-C
Low HDL-C
Odds Ratio
95% CI
Odds Ratio
95% CI
Odds Ratio
95% CI
Socio-demographic profile
Female gender
1.39
1.12–1.72*
1.26
0.98–1.62
0.59
0.46–0.74**
Age
1.00
1.00–1.01
1.00
1.00–1.01
0.99
0.98–0.99**
<
6 years’ formal education
0.68
0.56–0.84**
0.74
0.59–0.92*
1.56
1.24–1.96**
Soweto origin
0.83
0.67–1.02
0.86
0.69–1.07
0.93
0.74–1.15
Diabetes comorbidity
1.0
0.72–1.38
0.99
0.70–1.40
1.23
0.86–1.77
Current smoker
0.72
0.58–0.89**
0.68
0.54–0.85**
1.47
1.17–1.85**
Ethnicity
African ancestry (reference)
1.0
–
1.0
–
1.0
–
White European
2.17
1.36–3.46*
2.10
1.27–3.47*
1.01
0.61–1.68
Mixed ancestry
3.04
1.79–5.15**
2.44
1.41–4.22*
0.71
0.42–1.20
Indian
4.15
2.61–6.60**
4.66
2.72–7.97**
1.00
0.63–1.59
TC
=
total cholesterol; LDL-C
=
low-density lipoprotein cholesterol; HDL-C
=
high-density lipoprotein cholesterol; CI
=
confidence intervals.
Age-, gender- and body mass index-adjusted analysis: *
p
<
0.01; **
p
<
0.001.
