(Hypertension. 1996;27:108-113.)
© 1996 American Heart Association, Inc.
Articles |
A Survey of Blood Pressure Distribution in Pygmy and Bantu Populations in Cameroon
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.).
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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.
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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.
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Discussion |
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TopAbstractIntroductionMethods Results Discussion References |
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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/m2 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 19.49 in males and 18.87 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.
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Selected Abbreviations and Acronyms |
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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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References |
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