Equipc d’tkdogie hunmine, Laboratoire d’anthrofmiogic biologiquc, Uniuersite’ Paris 7, 2 Place Jurrieu, Paris, France
Variation of Blood Pressure and Heart RateInandBetweenEighteenEthnicGroups of Rwanda, Burundi and Zaire
Blood pressure and heart rate of 2095 adult males from Rwanda, Burundi and Zaire arc analyzed. The subjects were sampled from 18 rural ethnic groups which largely differ in their biotope, mode of subsistance and morphology. Each of the three variables: systolic BP, diastolic BP and HR varies significantly between the ethnic groups. The first two are closely intercorrelated, whereas mean HR varies independently of mean SBP. Mean HR varies indepen- dently of morphology (as represented by 5 anthropometric variables), whereas SBP is significantly correlated with calf circumference between populations, but not within populations. Mean HR varies independently of climate, whereas mean SBP is significantly and negatively correlated with annual rainfall. The general mean of SBP is low by French standards. The SDS are such that it looks unlikely that SBP increases much with age in any of the 18 popula- tions. All significant results concerning SBP can be explained by interpopulational variation in food intake. However, this variation explains only a part of that of mean SBP. A comparison of the conditions of life of those African populations in which SBP increases with age in adults and those in which it does not suggests that this process is a maladaptive response to a disturbed psychosocial environ- ment.
1. Introduction
Blood pressure and heart rate of 2095 natives of Rwanda, Burundi and Zaire are analyzed here in relation to 5 morphological variables and some environmental charac- teristics. All subjects were male adults whose apparent age ranged from the end of adolescence to the beginning of senescence. All blood pressure measurements were taken by one of us (J.H.) between 1950 and 1953, with a Baumanometer by auscultation on rested sitting subjects, just after heart rate had been recorded by auscultation.
The subjects were sampled from 18 rural ethnic groups. They lived in a large variety of environments: average altitude varying from 400-2700 m; the biomes represented are the savanna, the equatorial rain forest and the montane forest. Some groups were mainly pastoralists, some other ones subsisted mainly on agricultural products, and hunting or fishing provided a substantial amount of animal food to others. The 18 groups also largely varied in physique: from the small Twa pygmoids to the tall and elongated Tutsi.
2. Results
Distribution of blood pressure and heart rate in the 18 populations
Table 1 gives the mean and standard deviation of systolic and diastolic blood pressure and of heart rate in the 18 samples. Each of the three variables shows a highly signifi- cant inter-population variation (P < O-01).
Interpopulation correlation between the three physiological varzables
Between the means of systolic and diastolic blood pressure, the correlation coefficient is
Journal of Human Evolution (1979) 8, 767-771
0047-2484/79/080767 + 05 $02.00/O Q 1979 Academic Press Inc. (London) Limited
768 J. HIERNAUX AND A. SCHWEICH
Table 1 Sample &a (n), mean (f) and standard deviation (a) of systolic and diastolic blood pressure and heart rate in the 18 populations
SBP DBP HR (mm Hg) (mm Hg) (beats/min)
--- n R s s s a s Population
Tutsi (Rwanda) 177 116.83 13.84 73.57 9.56 75.36 15.26 Tutsi (Burundi) 119 119.10 13.75 72.54 9.58 78.04 14.10 Kiga Hutu (Rwanda) 70 128.21 13.94 73.21 9.79 66.00 13.39 Non-JGga Hutu (Rw) 184 124.60 13.84 73.42 9.36 50.84 15.66 Hutu (Burundi) 216 124.21 14.72 73.86 8.91 75.11 14.28 Twa (Rwanda-Burundi) 109 126.87 14.27 77.23 9.38 70.80 11.49 Tutsi (Itombwe) 100 1 IO.80 12.86 71.80 8.91 74.2 1 13.45 Havu 100 109.25 14.18 67.85 9.64 70.58 16.56 Hunde 100 117.55 13.66 72.35 9.65 73.27 15.53 Swaga 100 113.60 11.43 71.40 9.68 64.29 14.97 Shu 100 115.60 12.11 71.75 8.19 69.37 14.00 Mbuba 100 107.40 12.13 67.50 8.08 75.60 13.47 Nyanga 100 114.30 IO.70 67.80 a,37 72.48 13.47 Tembo 100 106.55 14.12 65.30 8.86 75.44 14.40 Rega 100 111.28 12.98 70.35 8.42 83.09 13.61 Fulero 100 114.82 14.97 70.00 9.63 69.43 12.44 Bushong 120 124.75 14.76 77.32 10.61 72.69 13.65 Twa Kuba 100 120.10 13.47 68.70 9.38 73.86 13.05
high: r = + 0.74 (2’ < O-01). The means of systolic blood pressure (SBP) and heart rate (HR) are correlated by an insignificant coefficient of I = -0.26 (P < 0.05).
Correlations of mean SBP and HR with jve morphological measurements
Table 2 gives the correlation coefficients between mean SBP or HR and the means of stature, body weight, biacromial diameter, calf circumference and right hand dynamo- metry, those of stature with the four other morphological measurements, and the coefficients of partial correlation of SBP with the four last variables when mean stature
is held constant.
Table 2 Correlation coefficients of mean systolic blood pressxnre and mean heart rate with the means of stature, body weight, biacro& diameter, calf circumference and right haml dynamometry. Correlation coeffideattm of mean stature with the means of the last 4 measurements, and partial correlation coeffidents of mean SBP with the latter when mean stature is held constant
SBP HR Stature
Stature
+0.10 + 0.08
Hand Weight Biacromial Calf strength
+0.36 +0.24 +0.56* +0*41 -0.02 - 0.08 $0.15 $0.01 + 0*54* + 0.42 +0*49+ $0.23
with stature held constant
SBP mV +0.59*+ $0.40
[*0*05 3 P > 0.01. **P G O.Ol.]
BLOOD PRESSURE AND HEART RATE 769
Heart rate does not correlate significantly with any of the five anthropometric variables; all its correlations are very low, under O-15, some positive and others negative. The interpopulation variation of heart rate appears to be independent of morphology and muscular strength.
The pattern of mean SBP’s correlation coefficients is quite different: all coefficients are positive, their mean is much higher, and one of them is significant at the 5 ‘A level: that of mean SBP with mean calf circumference (r = +0*56). When mean stature is held constant, its significance reaches the 1 % level (r = +0*59). This value contrasts with the correlation coefficient of SBP with calf circumference between individuals: in the 18 populations, it varies between -0.24 and 10.32, with a weighted mean of 1-0.08.
Correlations of mean SBP and HR with three climatic variables
Table 3 gives the correlation coefficient of mean SBP and HR with altitude, mean annual temperature, and annual rainfall. No correlation of HR is significant, whereas mean SBP shows a significant correlation with rainfall (r = -0.52).
Table 3 Correlation coefficients of mean systoloic blood preemue and heart rate with altitude, mean annual temperature, and annual rainfall
Altitude Temperature Rainfall
SRP +0*14 -0.08 -0.52” HR -0.28 +0.36 +0.21
3. Discussion
Comparison of mealES and standard deviations of SBP and HR in the 18 populations wath analogous
values in other populations of sub-Saharan Africa and in French series
Heart rate, which is known to be invariant with age during adulthood, has a general mean of 72 beats per minute in our total sample, near to the lowest French value recorded and lower than the only analogous value recorded in a large sub-Saharan African sample: 77 beats per minute in the Fali of Northern Cameroon. The variation of mean HR remains completely unexplained: it does not show any dependence on age, climate or morphology, and different levels of emotional response to the examination look like an unlikely explanation, even partial, of the observed variation. HR’s variance is higher in our set of populations than in the French series, another unexplained finding.
The general mean of SBP in our total sample (117 mm Hg) is lower than in France. Although the range of ages is much wider in our samples than in any of the French series, the standard deviation of SBP remains lower in our African populations. This makes it unlikely that, in these populations, SBP increases much with age, at least in the male sex. This inference is reinforced by the finding that the standard deviations of SBP in our samples are of the same order of magnitude as in age classes of 10 years’ interval in adult populations whose mean SBP has been proven to be independent of age. A weak or non-existent dependence of SBP on age has indeed already been noted
770 J. HIERNAUX AND A. SCHWRICH
in a number of African populations, in which mean SBP is also lower than in France. Other African populations show an increase of SBP with age. Our 18 samples seemingly belong to the first group.
IdentiJication of the f&or-s of variation of mean SBP
In this study, calf circumference has been selected for its high responsiveness to variation in caloric intake. How can we explain the contrast between the intra- and interpopula- tion correlation coefficients between this variable and SBP? We offer the following explanation: calf circumference and SBP are dependent on a factor (or complex of factors) which varies between populations but is relatively constant within each popula- tion; in a population, the two variables vary almost independently under the influence of their specific factors of variation. The most evident common factor is nutrition. Diet largely varies in quantity between the 18 populations, but it varies little between members of the same ethnic group. If this explanation is right, a moderate caloric intake favors a low SBP. The type of diet does not seem to matter much: the list of our 18 ethnic groups extended to those other African populations known to have a low and age- constant SBP includes hunter-gatherer, agriculturalist and pastoralist groups; the diet of some groups is rich in animal protein, that of other groups is poor in this nutrient; the diet is rich in vegetable fat in some groups, rich in animal fat in some other ones, and poor in fat of any source in still other ones. One of the populations on the list, the Hadza, drinks brackish water, which indicates that a higher salt intake does not inevitably induce a higher SBP.
The only other significant correlation of mean SBP is with rainfall (r = -0~52). The distribution of annual rainfall is discontinuous in our set of populations: it shows a group of low values (around 110 cm) covering the territory of 7 populations in the eastern savanna, largely distinct from the 11 other values (whose mean is 179 cm) concerning equatorial forest habitats. In the first subgroup, SBP and rainfall are
correlated by the significant value of +0*79, whereas their correlation is insignificant in the second subgroup (-0.16). The negative total correlation results from the first subgroup having a higher mean SBP (122 against 114 mm Hg). We offer the following explanation of this pattern: in the rather dry savanna, food production is strongly influenced by rainfall, a dependence that is nearly absent in the rain forest.
The only factor of variation of mean SBP suggested by this analysis is the state of nutrition, especially as it results from the balance between food intake and energy expenditure, with a possibility of a genetic factor influencing both SBP and soft tissue development. However, only 31% of the variation in mean SBP is explained by the variation in mean calf circumference; other factors than nutrition surely influence SBP. A comparison of the ways of life of those African populations which experience an increase of SBP with age and of those which do not, suggests that nutrition is not the key factor of this dichotomy. The African groups with age-constant SBP (whose mean is usually low, but not so in every group) have a common pattern oi social life: all are rural, they are little submitted to the pressure of those new ideas, techniques and behaviour patterns induced by the recent contact with intruding non-African cultures; social relations amongst them are largely regulated by tradition. Their human environ- ment is one in which stress from psychosocial tensions is reduced. Related groups in which this cocoon has been torn open show a higher SBP and an increase of SBP with
BLOOD PRESSURE AND HEART RATE 771
age: this has been observed in newly urbanized groups, and in rural groups whose psychosocial environment has been recently disturbed.
The results of this analysis are paralleled by those of several comparative studies outside Africa. It seems that industrial society, in its present state at least, subjects a large proportion of its members, and members of interacting human groups as well, to pressures and states of frustration or anxiety towards which they react by a sustained increase in their blood pressure. This seems to be a sign of maladaptation of present man to an environment generated by his sociocultural evolution.
Adapted from: Hiernaux, J. & Schweich, A. (1975). V ariation interethnique de la pression arttrielle et du rythme cardiaque au Rwanda, au Burundi et au Zaire (Kivu et Kasal). Bi~&tie Humaine 10, 33-53 (where the bibliography is to be found).
