Hypertension. 1996;27:108-113
(Hypertension. 1996;27:108-113.)
© 1996 American Heart Association, Inc.
A Survey of Blood Pressure Distribution in Pygmy and Bantu Populations in Cameroon
Hugo Kesteloot;
Ndjitoyap Ndam;
Satoshi Sasaki;
Mathurin Kowo;
Victor Seghers
From the Department of Epidemiology, K.U.-Leuven (Belgium) (H.K., S.S.);
Department of Gastroenterology and Nutrition, University of Yaounde (Cameroon)
(N.N., M.K.); and the Heart of Texas Cardiovascular Center, Killeen, Tex
(V.S.).
 |
Abstract
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Abstract A blood pressure survey was performed in isolated
Pygmy
communities and Bantu population samples living either in close
relationship
with the Pygmies or in separate areas within the same
region.
The Pygmies are still living as hunter-gatherers, whereas
the
Bantus rely on agriculture for food provision. Mean blood pressures
in
Pygmies were 130/85 mm Hg in males and 126/80 mm Hg in females
and
in Bantus were 137/87 mm Hg in males and 136/84 mm Hg in
females. In
spot urine the mean urinary sodium concentration
was higher in Bantus
than Pygmies (86 versus 37 mmol/L in males;
95 versus 56 mmol/L in
females). In the total population urinary
potassium concentration was
very high (150 mmol/L), calcium
concentration very low (0.4 mmol/L),
and urea concentration
low (6.9 g/L). After adjustment for age, height,
weight, and
sex, no racial differences in blood pressure were
present. Blood
pressure increased with age but body mass index did
not. Diastolic
pressure correlated significantly but
negatively with urinary
sodium in multiple regression analysis.
Our study demonstrates
that blood pressure increases with age in
hunter-gatherer populations
on a low to moderately high sodium diet
in the presence of a
low urinary excretion of calcium coupled with a
low protein
intake.
Key Words: blood pressure • sodium • potassium • calcium • magnesium • Negroid race
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Introduction
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Our present human
metabolism is primarily determined by the
need to
accommodate the nutrition that the human race has been
consuming for
the past several hundred thousands of years. This
nutrition was close
to that of hunter-gatherer populations,
of which only a few persist
on earth. To study this problem
of metabolic adaptation, we
examined the level of cardiovascular
risk factors in a
sample of a hunter-gatherer population of
Pygmies in Cameroon
together with two Bantu population groups,
one living in close contact
with the Pygmies and one living
separately. This article will focus on
the BP distribution in
these populations.
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Methods
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Population Characteristics
The Pygmies generally live in the
tropical forests in small
communities
of 60 to 100 individuals, including children. Two distinct
Pygmy
populations were examined. One was in the Mecasse region in
the
Dja reservation and consisted of three communities: two
separated by a
distance of 6 km and a third by a distance of
30 km. The closest
village was Bengbis, a subprefecture. The
second Pygmy population,
smaller than the first, was living
in the region of Lolodorf, at a
distance of about 80 km from
the first community. These populations are
still classic hunter-gatherers.
However, they hunt with rifles and
ammunition that they obtain
from the Bantu population living in close
contact, in exchange
for part of the game they collect. They also
obtain salt from
the Bantus. Salt is sold in the region in packs of 18
kg and
is iodine enriched. Both Pygmies and Bantus use salt when
available.
The Pygmies live in huts made of large leaves, and the
Bantus
live in huts of dried mud. We were unable to evaluate the
nutrition
of the Pygmies as we were not able to observe them while they
ate.
They have no food reserves and eat only when the hunters return
in
the evening after we had already left for our base camp (traveling
time,
3 hours) to store the serum and urine samples in a freezer.
As no
electricity was present in any of the villages or camps
we visited,
we used a generator to produce the necessary current.
Gas oil was
difficult to obtain and sold in quantities of 5
to 15 L in the
subprefectures. By eating together with the Bantus
and by interrogation
and looking at the available food items,
we learned that the basic
nutrition of Pygmies and Bantus consists
of complex carbohydrates,
plantain, and manioc, with some fruit,
especially bananas and mangos,
used in varying proportions.
The meat includes crocodile, monkey,
snake, or antelope game
and some eggs. River and well water, used
for drinking, is obtained
at a distance of 300 to 500 m from the camp
and is of moderate
quality. Both Pygmies and Bantus drink alcohol,
particularly
palm wine. We examined some samples of palm and raffia
wine,
and the alcohol content was 4.5 to 5.5 vol%. They also consume
some
stronger alcohol distilled from palm wine. The production
of
palm wine, however, is scanty, and distances of 2 to 3 km have
to be
covered for collection of the wine.
The Bantus feel superior to the
Pygmies. Some racial intermingling
occurs, especially Pygmy women living with Bantu men, but the reverse
does not occur. In the Bantu community polygamy is still common. In the
Lolodorf region some Pygmy women had recently left their clan,
presumably to live with Bantu men. Three communities of Bantus were
examined: one living in close contact with the Pygmies in the Mecasse
region, one living in the Lolodorf region, and a separate community
living in Bengbis. The data were gathered during two periods: January
through February 1994 and May through June 1994. Traveling is
difficult, and only one or two cars a month traverse the region
inhabited by the Pygmies. Although the area is situated only 3° to
4° north of the equator, the climate is tolerable partly because the
region is situated on a plateau at 700 to 800 m above sea level.
The
day before the start of the survey the communities were informed
about the goal of the survey: to study their nutritional status and the
distribution of cardiovascular risk factors.
Participation in the study was voluntary. There were four male Pygmy
settlements: three in the Mecasse region and a scattered one in the
Lolodorf region. No population statistics were available at any
location, so the exact participation rate could not be ascertained. Our
impression was that in three of the four Pygmy communities the
participation rate of the number of the tribe was about 100%. This did
not include the number of the tribe absent for hunting, which could
take between 1 and 3 days. In the fourth Pygmy community the
participation rate was about 50%. In that community a conflict of
authority existed, and only those individuals accepting the authority
of the tribal chief agreed to participate. In the Bantu population the
participation in the study was limited by time restraints and the
availability of items such as vials, syringes, and needles. Many more
subjects were willing to participate but could not be accommodated.
Participation was essentially on a first-come, first-served
basis. It was materially impossible to examine a random sample of the
population. Members of the team volunteered to be the first to give
blood in order to set an example. In all camps the clan leaders were
the first to participate, convincing the population of the innocuous
nature of the examination. The Bantus are able to communicate with the
Pygmies and acted as interpreters. Very few Pygmy children go to Bantu
primary schools. Although most of the Pygmies had never seen a doctor,
they did not seem to be overly impressed by our presence and were very
willing to participate. In contrast to the Bantus, however, they never
inquired about the results of the examination. The nutritional status
of both the Bantus and Pygmies was fair, although in children signs of
protein deficiency were present.
Anthropometric Measurements
Only subjects 12 years old or
older were included in the study.
Height, weight, and age were recorded. In the Pygmies exact
recording of age was impossible as they do not know their ages,
not even those of their children. A Bantu teacher estimated their ages
on the basis of some reference points in time. Age was estimated before
BP was measured. BP was recorded with subjects in the sitting
position with the use of an RR strain-gauge BP meter calibrated
against a mercury manometer. The first audible Korotkoff sounds were
taken as SBP and phase V Korotkoff sounds as DBP. About 90% of all BP
measurements were taken by one examiner (H.K.). When phase V Korotkoff
sounds were still audible at nonphysiological
levels of DBP (muffled sounds present at less than half of SBP),
phase IV was recorded. The cuff measured 22x12 cm. The same BP
meters have been used in previous research in Korea and
China1 2 and in other epidemiological
studies.3 BP was recorded twice, to the nearest 2
mm Hg, and the mean of the two measurements was calculated. HR was
measured over a 30-second period, and BP was measured about 10 minutes
after collection of the blood sample. Nine BP measurements and 26 HR
measurements were missing.
Biochemical Samples
In all participants two blood samples of
approximately 8
mL were collected. These were allowed to clot, and the serum was then
separated by hand centrifugation over a period of 5 to
7 minutes. The time necessary to put the samples in a freezer was
maximally 8 hours. In all participants a spot urine sample was also
collected and put in the freezer after maximally 8 hours. The
biological samples were collected under nonfasting conditions between
10 AM and 3 PM. Determination of urinary cation
and creatinine values was performed in the Central
Laboratory of the University of Leuven, Belgium, according to the
INTERSALT protocol.4
Statistical Methods
Data were analyzed with Student's
t
test for calculation of the significance of differences in mean values.
Univariate and multiple regression equations (backward
stepwise regression) were calculated with significance at the .05
level. When interaction terms with sex, race, and sexxrace were
included in the multiple regression analysis, age, BMI, and HR
always remained significantly correlated with SBP and DBP. The final
R2 with all interaction terms included was only
slightly higher. ANOVA including sex, race, sexxage, racexage, and
sexxracexage showed that only sex was significant for SBP. With
the
use of the linear model procedure and introduction of group (n=4: Bantu
male, Bantu female, Pygmy male, and Pygmy female) and groupxage as
supplementary independent parameters, these variables
never attained statistical significance. We also analyzed
pooled data. The most robust equation was obtained between BP and age,
HR, BMI, and sex. The variance inflation factor was for all significant
independent predictions around 1.0.5 As a result, only the
equation including these parameters was retained in the
final multiple regression analysis.
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Results
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The results of the anthropometric and spot urine data of the
Pygmy
and Bantu subjects are given for race and sex in Tables
1
and
2
according to tertiles of age. The
results of the total
population divided according to race and sex are
given in Table
3
. Table 4
presents
selected results for the different regions.
The Bantus living in the
Bengbis region do not have close contact
with the Pygmies. They are
more urbanized and use more advanced
agricultural methods.
BMI was low. Albumin and glucose, measured by the Lab-stix
method (Bayer Diagnostica), were not present in any of
the urine samples. The results of the multiple regression
analysis for the total population are given in Table 5. In the
multiple regression analysis both SBP
and DBP correlated positively and significantly with age, weight, HR,
and sex. When for both SBP and DBP sodium, potassium, calcium, and
magnesium were replaced in the multiple regression analysis by
the ratios of sodium-potassium and calcium-magnesium, or by
sodium-creatinine,
potassium-creatinine,
calcium-creatinine, and
magnesium-creatinine, none of these variables
attained the .05 level of significance. After adjustment for age and
BMI, race was never a significant determinant of BP. The partial
regression coefficients of BP with age—adjusted for height;
weight; HR; and urinary sodium, potassium, calcium, magnesium, and
urea—are given in Table 6. In six of eight
equations, in both the initial and final equations of the multiple
regression analysis, BP correlated significantly and positively
with age. When the population was divided into two groups, 18 years or
older and less than 18 years, to avoid the problem of BP changes during
adolescence, the relation between BP and age was significant in the
older (P<.0001) and younger (P<.003) age
groups. No significant relationship in either sex or race between BMI
and age could be established. The correlation matrix of the urinary
values of sodium with potassium, calcium, magnesium, and
creatinine is given in Table 7. The
correlation between sodium and calcium was not stronger than that of
sodium with potassium and magnesium.
|
Discussion
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The anthropometric characteristics of Pygmies are similar to
those
of other hunter-gatherer populations.
6 Their BMI is
low
and does not increase with age, potassium intake is very high,
and
urinary calcium concentration is very low.
6 The maximum
potassium
concentrations in the urine were very high in the present
populations:
320 and 306 mmol/L in Bantu males and females and 248 and
386
mmol/L in Pygmy males and females, respectively. As a result,
both
the urinary sodium-potassium and calcium-magnesium ratios
were
very low. The BMI values of 20.0 and 19.8 kg/m
2 obtained
in
the present survey in Pygmy males and females, respectively,
are
slightly higher than the values obtained in other anthropological
surveys
of 18.8,
7 19.9,
8 and
19.4
9 in males and 18.8
7 in females.
The
Bantus of the Bengbis region, who do not live in close contact
with the
Pygmies and live in a more urbanized area, tended to
have higher
urinary sodium and BP and lower urinary potassium
levels. In the Bantu
population of the Bengbis region, frank
hypertension with SBP/DBP
greater than 160/95 mm Hg was not
uncommon, and very high BP values up
to 260/140 mm Hg were occasionally
found in subjects not participating
in the survey. In contrast
to other hunter-gatherer
populations,
10 11 12 the Pygmies had
relatively
high BP
values, with a BP significantly increasing with age
in females. The
increase of BP with age is universal in the
Bantu population. In the
Pygmies the data could be biased by
the absence of the young,
presumably healthiest members of the
tribe who were hunting. This could
influence the data for males
but not for females. The urinary cation
values should be evaluated
with necessary reservations, as only spot
urine samples were
obtained. Spot urine samples have been shown to be
of value
for the study of the relationship between urinary cations and
BP.
13 14 15 16 A correction
based on the expected 24-hour
urinary
creatinine value was not attempted, as the actual
24-hour urinary
excretion of creatinine in Pygmies is
unknown. Based on the
concentration of creatinine per
liter, a correction by a factor
of 1.2, for both males and females,
would appear to be justified
in order to extrapolate the 24-hour urine
excretion. However,
Yanomamo Indians have apparently very low 24-hour
urinary creatinine
excretion
levels,
10 11 12 13 and
thus the problem remains unsolved.
The BMI of the populations examined
was low and did not significantly
increase with age. It did, however,
significantly influence
BP (Table 5
).
The urinary sodium concentrations in the examined populations were low
compared with those in Western populations. Notwithstanding this
finding and the absence of an increase of BMI with age, an increase of
BP with age could be established. The low urinary calcium concentration
in Pygmies and Bantus was unexpected. The Paleolithic diet is
considered to contain 1500 to 2000 mg calcium per day, mostly from
plant origin.17 This is much higher than the calcium
content of Western food, which delivers about 800 to 1000 mg calcium
per day. In the INTERSALT Study6 only the Yanomamo Indians
and the populations of Papua New Guinea had urinary calcium values
approaching the values obtained in the present study. A high intake
of fruits and vegetables in both the Pygmy and Bantu populations is
reflected by the high urinary potassium concentrations.
Evidence exists showing an increased effect of sodium on BP in subjects
with a low calcium intake.18 19 20
Evidence also exists
showing a BP-lowering effect of
potassium.1 2 21 22
However, the estimated very high potassium intake in the present
study populations, higher than that in any of the INTERSALT
populations, did not result in low BP levels. Moreover, urinary sodium
concentration correlated significantly and negatively with DBP
(P=.004). This finding is difficult to explain. It should be
mentioned that in the INTERSALT Study in 2 and 3 of 52 centers sodium
correlated significantly and negatively with SBP and DBP,
respectively.3 The question arises whether the relatively
high BP could be related to stress caused by blood drawing. BP was
measured about 10 minutes after blood samples were drawn. Moreover, our
presence and our equipment could also have had an effect on their BP
levels. However, the participating subjects were quite relaxed; very
willing to participate; rested for 10 minutes before the BP
recording, which was made after blood was taken; and had HR
values similar to those of the Yanomamo Indians (78 beats per minute in
men and 84 in women). In the Yanomamo Indians, however, SBP/DBP values
were 105/65 and 91/57 mm Hg in men and women,
respectively.10 In the INTERSALT Study, SBP/DBP values in
the Yanomamo Indians were 101.3/64.7 mm Hg in men and 90.7/56.4 in
women.12 BP has been measured in the Pygmies in three
surveys. In a small survey of 12 men SBP/DBP was 99/64
mm Hg9 ; in another survey of 46 male Pygmies SBP/DBP was
120/71 mm Hg.8 These values were obtained with subjects
in the sitting position before an exercise test. At maximal workload
SBP/DBP increased to 180/73 mm Hg.8 In an early and
interesting study in Northeastern Zaire of a large number of Pygmies
older than 10 and up to 59 years old (108 men and 108 women), SBP
increased with age from 120.4 to 128.0 mm Hg in men and from 127.7 to
140.7 mm Hg in women. In men DBP increased with age from 74.7 to 78.6
mm Hg and in women from 71.1 to 84.9 mm Hg.23 With the
use of the weighted mean value of BP obtained in the 10-year age
classes, a significant rise in SBP and DBP with age (both
P<.05) in women and a borderline significant rise of SBP
with age (P<.08) in men could be calculated. The authors
also discussed the evolution of BP with age but did not reach a
definite conclusion. Compared with the present study the SBP values
are similar and the DBP values lower. It should be noted that in
tropical areas with a humid and warm climate, DBP is difficult to
measure.23
Whether the low intake of animal protein, especially during childhood,
contributes to the relatively elevated BP remains unknown. A high
protein intake appears to be associated with a low BP, both
experimentally24 25 and in humans.26 The
results of the BP survey together with other results and dietary
recommendations have been communicated directly to the populations that
participated in the present study.
In summary, BP in the examined Pygmy and Bantu populations was higher
than expected from the urinary concentrations of sodium and potassium.
BP increased significantly with age. The urinary excretion of calcium
was very low and of potassium very high. No racial differences in BP
between Pygmies and Bantus could be established. Further studies of the
determinants of BP in hunter-gatherer populations are
warranted.
|
Selected Abbreviations and Acronyms
|
|---|
| BMI |
= |
body mass
index |
| BP |
= |
blood
pressure |
| DBP |
= |
diastolic blood
pressure |
| HR |
= |
heart
rate |
| SBP |
= |
systolic blood
pressure |
|
|
Footnotes
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Reprint requests to H. Kesteloot, Department of Epidemiology,
K.U.-Leuven,
B-3000 Leuven, Belgium.
Received August 14, 1995;
first decision September 5, 1995;
accepted September 5, 1995.
|
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Top
Abstract
Introduction