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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 25, No 6, November/December 2014
AFRICA
275
hand, in the USA, there were 26.7 physicians and 98.2 nurses and
midwives per 10 000 individuals.
26
These low healthcare provider-to-population ratios (61/100 000 in
the Gambia and 19/100 000 in Sierra Leone) reflect the inadequate
establishment and funding of public healthcare facilities in these
countries. It is estimated that by 2015, according to the needs-
based model, there will be a total of 45 countries in the world with
physician shortage, 32 countries (~ 70%) of which are in Africa.
43
Potassium and sodium levels and SES
HTN is related to sodium and potassium levels based on renin
secretion, cellular sodium–potassium pumps and therefore the
individual’s nephron mass. The effect of sodium and potassium
levels on HTN in the Gambia and Sierra Leone depends on
two factors: the intrinsic propensities of the individual being
of African descent and the individual’s levels of salt intake, as
well as vegetable and fruit (potassium) intake. Research in the
USA and Europe illustrated that people of African descent had
higher HTN prevalence and were at a higher risk of acquiring
organ damage due to HTN,
23
in part because of lower nephron
mass, macula densa mass, sodium detection levels and sodium–
potassium pump activity.
17,44,45
It was found that higher SBP and DBP means were apparent
in individuals with higher sodium intake levels when compared
with either intermediate or low sodium intake.
46
It has been
shown that there is a linearly increasing correlation between
sodium intake and HTN prevalence and mean SBP.
47,48
Globally,
it was estimated that sodium intake in children older than five
years of age was in excess by about 100 mmol/day.
49
This was a
significantly high sodium intake level, considering that a high
level of salt intake in infancy and childhood correlated to a high
BP later in life.
50,51
In central and South Africa, it was found
that sodium levels in cells and in circulating blood were high in
hypertensive individuals.
18
In the Gambia, intake of salt-preserved foods was high due
to inadequate refrigeration. As a consequence, there was a high
salt and sodium intake.
23
A low SES reduces the likelihood for
a household to own a refrigerator and to receive electricity. In
the Gambia, 14% of 50 females aged 14–25 years and 34% of
50 males aged 35–50 years did not receive electricity at home.
42
This electricity grid showed inadequate electricity reception in
Gambian households, leading to an inability to refrigerate foods.
Furthermore, dietary potassium intake was related to BP.
52
Studies compared sodium to potassium intake and showed that in
lower SES communities, the ratio between sodium and potassium
intakes was high; however, the situation was nearly reversed in
higher SES groups because potassium intake was higher than that
in lower SES groups.
40
In Ghana, it was shown that an insufficient
fruit and vegetable (a source of potassium) intake in 39.6% of
males and 38.2% of females was considered a factor contributing
to HTN prevalence.
53
Therefore, this low potassium intake assists
in maintaining a high HTN prevalence rate.
Psychosocial status and SES
One of the factors contributing directly to an increased HTN
prevalence is the psychological status of the individual, affected
by stressors correlating with low SES. Studies have shown that
stress, economic transition, and high BP may be correlated.
25,54
As noted by a recent study, there is a significant association
between psychosocial stress and endothelial dysfunction, which
contributes to the development of CVD.
24
The study found that
cold stress caused a more prominent increase in DBP in white
South Africans compared to black South Africans. In addition,
black Africans who reported higher levels of psychosocial distress
had lower L-arginine/ADMA (asymmetric dimethylarginine)
ratio. ADMA is known to be an inhibitor of the endothelial
NO synthase, which produces NO from L-arginine. The study
concluded that psychological distress significantly affects the
L-arginine/NO system, with some ethnic differences.
24
In a low-SES community, employment levels are very low,
therefore leading to an increase in stress levels for individuals
in a household due to the lack of an income source to support
a living. Another possible source of stress in the Gambia and
Sierra Leone was the instability in both societies. The instability
in Sierra Leone was due to the persisting civil war from 1991
to 2002, while in the Gambia, it was due to their increasing
potential population due to the outmigration of Sierra Leoneans
to surrounding countries, one of which was the Gambia. This
instability could have served as a psychological stressor that led
to the increase in HTN prevalence in both populations.
Additional HTN risk factors
Additional possible risk factors for HTN include smoking,
alcohol consumption, schistosomiasis specifically in the Gambia,
and certain genotypic correlations. Smoking is associated with
CVD and increases HTN risk by two- to three-fold.
55
In the
Gambia, by 2006, 29.2% of males and 2.6% of females were
tobacco smokers, compared to the USA, where 25.4% of males
and 19.3% of females were tobacco smokers.
26
Alcohol intake also contributes to a higher BP and the
prevalence of HTN.
56
A study in Uganda considered past and
present alcohol intake as a risk factor associated with HTN
prevalence.
30
As for the Gambia and Sierra Leone, by 2005, the
total alcohol consumption among adults aged
≥
15 years in the
Gambia was 2.4%, while in Sierra Leone, it was 6.5%, compared
to 8.5% in the USA.
26
In the Gambia, schistosomiasis was another risk factor.
Studies showed that prevalence of diastolic hypertension in
adults was two- to four-times higher in
Schistosoma haematobium
endemic areas,
23
including parts of the Gambia and Sierra Leone.
Regarding genotypic influences, recent studies relate certain
loci and some single nucleotide polymorphisms in the human
genome to BP and HTN. An admixture mapping study identified
a probable relatioship between chromosomes 6q24 and 21q21
and HTN risk in African Americans.
57
These two regions
included two loci on chromosome 21q, and five other markers on
chromosome 6q that suggested a genetic linkage to elevated BP.
One genome-wide association study (GWAS) related three
genes, previously associated with BP in Americans of European
descent, with BP in African Americans.
58
The three genes were
SH2B3
,
TBX3-TBX5
, and
CSK-ULK3
, all of which are genetic
variants influencing BP in African Americans, and generally in
people of Africa descent.
Influences of lifestyle and economic development
Lifestyle changes, including smoking cessation, lower alcohol