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Cardiovascular studies in the Samburu tribe of Northern Kenya
Clinic al communications
Cardiovascular in the Samburu
studies tribe of Northern
A. G. Shaper, M.B., Ch.B., M.R.C.P., Kampala, Uganda
T
tribe of his study of the Samburu Northern Kenya has been undertaken with the purpose of assessing some of the physical and cardiovascular characteristics of a nomadic people who live on a diet of milk and meat, and who are physically very active. Relatively few studies are available concerning blood pressure and body build in similar population groups living in the tropics and subtropics; there have been no studies on blood lipids or electrocardiographic patterns and no autopsy studies. In view of the uncertainty which still exists concerning the relationship between environmental factors (e.g., physical activity, dietary pattern), blood lipids, and coronary athersclerosis, there is clearly a need to investigate fully the possible effects on blood lipids and on coronary heart disease of large muscle activity in persons and groups ingesting diets which, in theory, are potentially atherogenic. This work has been in the nature of a pilot survey, that is, an attempt to assess whether more prolonged and elaborate investigations are warranted either in this particular society or in similar social groups still in existence in Africa. Socioeconomic background of the Sambum. The Samburu are a nomadic NiloHamitic tribe living in the Northern Province of Kenya and dependent entirely on
D.T.M.
Kenya & I$.
their herds of cattle, sheep, and goats for their economy and livelihood; agriculture is completely absent from the society. Every adult male belongs to a particular age set, and the time of his initiation into that age set determines his sub-age set; each of these separate groups has a specific name. The three main groupings are boys, warriors, and elders, and with a detailed knowledge of this social organization it is possible to make a fairly accurate assessment of individual ages. Physical activity. At all age levels there is a fairly high degree of physical activity associated with the herding, watering, and grazing of cattle. Family migrations usually take place every 6 weeks or so; the whole settlement moves about 10 to 1.5 miles, whereas, seasonally, cattle may be driven by the younger men to areas 50 or even 100 miles distant in search of grazing or water. The task of herding the main stock is undertaken by older boys, warriors, and elders, and a day’s herding may involve a trek of up to 20 miles. Warriors and elders who are not herding will assist with watering cattle, and this may involve lifting 400 gallons of water 4 or 5 feet by hand every other day, using only a wooden bucket. Long distances are traveled by the warriors in their wanderings around the countryside, and they may walk 30 miles
From the Department of Medicine, Makerere College Medical School, Kampala, Uganda. This study was made possible by grants from the United States Public Health Service Research Grants Committee, and the East African Council for Medical Research. Received for publication May 18, 1961.
437
(H-4791).
Makerere
College
438
Am. Hcavt I. April, 1962
Shaper
or more a day in the hot sun, for several days in succession. The early years of elderhood are usually harsh and exacting, and as a man grows older his physically active role becomes less marked, although he will spend a considerable amount of time in search of lost cattle or visiting nearby settlements or villages. Diet. The diet consists almost entireI> of milk and meat. Blood is a variable and minimal part of the diet and is used to any extent only during the dry season. Carbohydrates are practically absent from the diet of the warriors and elders, and vegetables are eaten only in very small quantities. The warriors may drink sotne 4.5 to 7 liters of milk at a single sitting, and, during the wet season, when milk is plentiful, they will do this twice a day; the amount will diminish to a total of 2 to 3.5 liters a day or even less in the dry season. Meat may be taken infrequently when tnilk is abundant and once or twice a week in the dry season. The elders drink less milk than do the warriors and take meat more regularly, for unlike the warriors they are under no ritual prohibitions. Serniquantitative assessments indicate a high-fat, high-protein, and low-carbohydrate diet, but there is clearly a marked seasonal variation in intake. The average fat content of several specimens of Samburu milk examined was 5.6 per cent, and, allowing for daily intakes of 3.5 liters for boys and elders and of 7 liters for warriors and young elders when supplies are adequate, this will give daily intakes of 196 and 392 grams of fat, respectively, providing at least 60 per cent of total caloric intake. In regard to the Samburu district as a whole, milk is probabl? abundant for some 4 months of the year, sufficient for needs during an additional 4 months, and insufficient during the remaining 4 months when meat has to be used to supplement the diet. Even though cattle and small stock are, in theory, available to maintain food intakes during periods of inadequacy, cultural patterns are such that animals are not readily slaughtered even in time of need, and imported foodstuffs (e.g., maize meal) are by custom not taken by adult males. Thus, the high-fat, high-protein diet varies quantitatively with the seasonal variations in
supply, and periods of frank famine not unknown in the Samburu territory. Material
and
are
methods
This study was carried out in the Maralal-K’amba area of the Northern Province of Kenya during April, 1960. There had been an exceptionally severe dry period before our visit, but slight rain had fallen in December, 1959, and more rain fell in March and April, 1960. The survey was restricted to males, and, in all, 105 warriors (age range of 16 to 31 years; mean age of 26 years) and 178 elders (age range of 34 to 90 years; mean age of 47 years) were studied. Ages were assessed by Paul Spencer, an anthropologist who had lived for over 3 years as a member of the Samburu tribe. This was clone b\ascertaining the age set and sub-age set df each subject, and the method was considered to be accurate to within 2 years for the majority of subjects. All subjects were weighed and their heights measured. Blood pressures were recorded by one observer” after the subjects had been seated for several minutes with the cuff in position. The lower of two to three readings was recorded and the diastolic pressure was read at the onset of the fourth phase. Electrocardiograms were obtained on 100 subjects (age range of 34 to 90 years; mean age of 48 years), using a direct-writing transistor cardiograph operated by batteries. Tracings were onl) recorded with the subjects at rest, and chest leads were limited to Vz, V4, and Vs positions. The following estimations were carried out on samples of venous blood obtained in the morning: total cholesterol (l), lipid phosphorus (2), triglycerides (3), and total fatty acids (4). Information on diet was compiled from the personal experience of Paul Spencer, and from repeated and detailed enquiries made by mvself during this survey and on earlier visits to the area. No formal survey of diet has been attempted in this nomadic group, but this is to be carried out in the near future by the Kenya government. Results
The majority of the males were on the lean side; the warriors were slender rather
Cardiovascular
studies in Samburu tribe of Northern
than muscular in appearance, and only a few individual elders were observed who could be considered to be overweight. AA 19-year-old male had a congenital heart disorder (probably Fallot’s tetralogy) ; another of the same age had clinical evidence of right ventricular hypertrophy, and still another one, a 31-year-old warrior, had early mitral incompetence with slight left ventricular hypertrophy. No clinical evidence of cardiovascular disease was noted in any of the elders examined, although peripheral arteriosclerosis was not uncommon in the older subjects. Body build and blood pressure. The Samburu are predominantly lightweight individuals, and with increasing age, no increase in average weight is recorded. The mean height for all the males is 68.9 inches (SD. 2.9 inches), and the mean weight of 126.2 pounds (SD. 14.0 pounds) remains remarkably constant in each decade of life from the third onward. The average increase in weight for each inch of increase in height is 1.7 pounds; this is about one third of the increase seen in American males5 Comparison of American and Samburu average weights by age (with due allowance for clothing) shows a difference in mean weight at 20 to 29 years of 25 pounds; this difference increases to 34, 38, and 39 pounds, respectively, in the subsequent three decades and falls slightly to a difference of 35 pounds in the 60 to 69-year period. Almost nine tenths of the Samburu males are less than 90 per cent of American average weights for their height and age. Data on blood pressure in adult male Samburu are given in Table I. The systolic blood pressure is significantly lower than that of Americans” at all ages and shows no increase with increasing age from 20 to 59 years. A rise in systolic pressure is recorded in the over-60 group. Corrected for differences in method, diastolic pressures in the Samburu are lower than those in Americans at all ages and fall significantly in the Samburu after the age of 49 years _ . Levels of plasma lipids. The mean levels and standard deviations of the four lipid components studied and the ratio of cholesterol to phospholipids (C/P) are shown
h-enya
439
by age decades in Table II. When warriors and elders are compared as two separate no statistically significant differgrow, ences can be demonstrated between the mean levels in any of these components,6 although when grouped according to age decades as in Table I I there is a statisticall> significant fall in the 50 to 59 group in both total cholesterol and levels of phospholipids, with corresponding changes in the C/P ratio. The level of cholesterol remains lowered into the over-60 group, whereas the level of phospholipids rises again in this age group. Electrocardiographic j&dings. Electrocardiograms were obtained on 100 elders (age range of 34 to 90 years; mean age of 48 years). No gross cardiovascular disease was noted in any of these elders. Only 3 subjects had an elevated diastolic blood pressure (135/95; 145/100 mm. Hg), but without evidence of left ventricular hypertrophy, and in these 3 subjects the electrocardiogram was normal. Possible ischemic patterns were seen in 2 subjects-one aged 52 years with slight T-wave inversion in several leads, and one aged 81 years with a left bundle branch block. In neither of these two subjects did the tracings show conclusive evidence of myocardial disease. Moderate flattening of T waves without inversion or other significant changes were noted in 7 other subjects. Discussion
Is the rise in systolic and diastolic pressures seen in so many populations a “normal” phenomenon, or is it a reflection of Table 1. Blood pressure by age in adult male Samburu. Afean systolic and diastolic levels and standard deviations .4 ge decades
NUW ber ~
20-29 30-39 40-49 50-59
f-50+ *Diastolic
Syhdic
S.D.
111.5 112.3 112.2 109.2 116.6
10.8 12.3 11.1 10.3 14.1
’
Diasto1ic*
S.D.
76.5 76.7 78.8 74.9 74.8
7.0 8.1 8.1 7.6 7.2
~ 41 79 54 43 22
readings
recorded
as fourth
phase.
440
Am. Heart J. Afiril, 1962
Shafler
Table II. Plasma lipids in adult Samburu males (in milligrams and standard deviations)
per 100 ml. with mean values
Age decades Total 15-19 Number of subjects
1
20-29
1 30-39
1
10-10~~0-59
1
60+
13
52
66
33
27
10
Total cholesterol Mean SD.
164.0 42.6
168.0 39.4
170.0 38.8
168.0 37.9
153.0 33.0
144.0 38.1
166.0 39.2
Phospholipids Mean SD.
208.9 37.9
207.2 37.9
214.5 33.3
226.1 32.2
193.0 29.5
223.4 12.8
212.0 34.5
C/P ratio Mean S.D. Total fatty acids Mean SD. Triglycerides Mean SD.
0.79 0.15
0.83 0.02
0.80 0.11
0.74 0.15
0.79 0.12
0.69 0.12
201
0.79 0.14
243 52.0
256 60.4
2.51 76.9
260 48.3
244 41.9
242 44.9
254 58.1
74.0 7.8
83.5 40.4
86.0 38.6
83.5 7.8
84.0 6.8
97.0 41.9
85.0 31.9
the incidence of hypertension in the communities observed? Studies within East Africa’ indicate that although large increases in blood pressure with age are unusual, significant variations in mean levels of blood pressure and in the relationship of blood pressure to age may occur from one tribal and geographic area to another, whereas a study in West Africa has indicated a close parallel between American and African patterns of blood pressure.8 In a recent review of blood pressure in relation to age and sex in the tropics and subtropics, Lowensteing discussessome 26 references concerned with various ethnic and social groups. He considers that those of the groups reviewed which show no increase in mean blood pressure with age during adult life represent relatively small homogeneous populations living under primitive conditions, more or less undisturbed by their contacts with civilization. The rise in blood pressure seen with age in most of the groups he reviews is, in his opinion, ‘la consequence of civilisation or the process of acculturation.” From a study of Bushmen in the Kalahari, Kaminer and LutzlO
also conclude that a rise in blood pressure is not a characteristic of a normal aging process, and regard it as an indication of the existence of essential hypertension in a community. Our findings in the Samburu would suggest that an increase in weight and a rising blood pressure are not necessary accompaniments of the aging process. The rise in systolic blood pressure seen in the seventh decade in the Samburu is not due to the presence of hypertension in this group and may be a manifestation of decreased elasticity of the aorta and larger blood vessels. The mean level of plasma cholesterol for all Samburu males is comparable to that found, by an earlier study, in healthy adult African males of Kampala, Uganda, who were living on a diet to which fat contributed 10 to 15 per cent of the total calories.ll Most recent investigations into dietary patterns and blood lipids have shown that the customary dietary habits of communities are usually reflected in their mean levels of serum cholesterol, and that increases in the consumption of
Vohme Nwwber
63 4
Cardiovascular
studies in Samburu
animal fat lead to approximately parallel increases in the mean levels of blood cholesterol. In the light of the dietary pattern described in the Samburu tribe, their levels of cholesterol seem to be contrary to this thesis and require explanation. The mean levels of phospholipids, total fatty acids, and triglycerides are also in keeping with levels found in groups on lower fat diets6 Initially, an attempt must be made to answer the question whether differences in habitual physical activity could account for the variations in the concentrations of blood lipids in different populations, and, in particular, whether this factor might be responsible for the unexpectedly low levels of lipids in the Samburu. Reviewing at length the data from many countries, Keys*2 concludes that physical activity does not explain the large differences in concentrations of serum cholesterol observed between populations eating different amounts of fat. This is not to deny the possibility that physical exercise plays some part in regulating the concentration of lipids in the blood, but it does not appear to be a major regulating mechanism. It seems reasonable to suggest that the low levels of blood lipids found in the male Samburu are, in the main, associated with the quantitative variability in their highfat diet, and that their high degree of dynamic physical activity does not by itself account for these findings. The findings on blood lipids in the Samburu would suggest that for a high intake of butter fats or other saturated fats to produce abnormally high levels of lipids in the blood, the intake must be habitual and, probably, must be part of a lifespan pattern of diet. Although the number of Samburu studied by electrocardiography is far too small to allow any conclusive statement to be made concerning the relative frequency of the complication of coronary heart disease, there is at present no autopsy information available from this tribe. All we can suggest at the time of writing is that the complications of coronary atherosclerosis, as evidenced by our electrocardiographic findings, are apparently uncommon in the adult male Samburu. Even though minor changes suggestive of ischemia are noted, it must be remembered that
tribe of Northern
Kenya
441
in some parts of Africa there is convincing evidence that electrocardiographic changes which in Europe would be interpreted as indicating ischemic heart disease may be found in a large proportion of healthy subjects.13J4 It is clearly undesirable to rely solely on this relatively small electrocardiographic survey, and supporting pathologic information is being sought. By the accumulation of data concerning peoples who live in special environmental situations and at different levels of “civilization,” studies in geographic pathology, such as the present one, may lead to a better understanding of some of our cardiovascular problems, e.g., essential hypertension and coronary atherosclerosis. Although the urgent requirement is for adequate autopsy material which can be correlated with clinical and biochemical information, this is seldom if ever available in areas such as we have described, and by the time that adequate pathologic facilities are available it may well be that the way of life has been significantly altered as regards dietary habits and patterns of physical activity. It must be emphasized that this has been an uncontrolled pilot study. In order that more definite conclusions may be reached, seasonal studies as well as individual absorption studies are now being carried are being out, and direct comparisons made with other groups in East Africa. The results of these more extensive studies will be reported later. Summary
The Samburu tribe of Northern Kenya live on a diet of milk and meat and are physically very active. There is no increase in weight with age, and only a small increase in weight with advance in height. They show no rise in systolic blood pressure until the seventh decade, and diastolic pressures fall after the fifth decade. Levels of lipids in the blood are comparable with those found in groups living on low-fat diets, and it is suggested that this phenomenon is related to the seasonal variation in supply. Initial electrocardiographic studies suggest a low incidence of coronary heart disease. Further studies are in progress to investigate more fully the many questions raised by this initial survey.
442
Am. Heart J. Afiril, 1963
Shaper
The members of this expedition included Professor A. W. Williams, Dr. P. G. Wright, Mr. J. Kyobe, and Mr. P. Spencer. Without their energetic participation this work would not have beenpossible. We wish to thank the District Commissioner. Samburu District, for permission to conduct this survey in the Maralal-Wamba area, and the Department of Physiology for the use of their mobile laboratory (Wellcome Trust). REFERENCES 1. Abell, L. L., Levy, B. B., Brodie, B. B., and Kendall, F. E.: A simplified method for the estimation of total cholesterol in serum and demonstration of its specificity, J. Biol. Chem. 195:357, 1952. 2. Bartlett, G. R.: Phosphorus assay in column chromatography. Modification of Fiske and Subba Row method. 1. Biol. Chem. 234:466. 1959. 3. Van Handel, E., and Zilversmit, D. B.: Micromethod for determination of serum triglycerides, J. Lab. & Clin. Med. 50:152, 1957. 4. Stern. I.. and Shaoiro. B.: A raoid and simole method ‘for the -determination’ of esterihed fatty acids and for total fatty acids in blood, J. Chn. Path. 6:158, 1953. 5. Shaper, A. G., Williams, 4. U’., and Spencer, ”
P. : Blood pressure and body build in an African tribe living on a diet of milk and meat, East African M. J., 1962 (in press). 6. Shaper, A. G., Jones, M., and Kyobe, J.: Plasma lipids in an African tribe living on a diet of milk and meat, Lancet 2:1324, 1961. 7. Williams, A. W.: To be published. 8. Abrahams, D. G., Alele, C. A., and Barnard, B. G.: The systemic blood-pressure in a rural West African community, West -4frican M. J. 9:4.5, 1960. 9. Lowenstein, F. W.: Blood pressure in relation to age and sex in the tropics and subtropics, Lancet 1:389, 1961. 10. Kaminer, B., and Lutz, W. P. W.: Blood pressure in Bushmen in the Kalahari desert, Circulation 22:289, 1960. 11. Shaper, A. G., and Jones, K. W.: Serum cholesterol, diet and coronary heart disease in Africans and Asians in Uganda, Lancet 2:534, 1959. 12. Keys, A.: Diet and the epidemiology of coronary heart disease, J.A.M.A. 164:1912, 1957. 13. Grusin, H.: Peculiarities of the African’s electrocardiogram and the changes observed in serial studies, Circulation 9:860, 1954. 14. Powell, S. J.: Unexplained electrocardiograms in the African, Brit. Heart J. 21:263, 1959.
Cardiovascular in the Samburu
studies tribe of Northern
A. G. Shaper, M.B., Ch.B., M.R.C.P., Kampala, Uganda
T
tribe of his study of the Samburu Northern Kenya has been undertaken with the purpose of assessing some of the physical and cardiovascular characteristics of a nomadic people who live on a diet of milk and meat, and who are physically very active. Relatively few studies are available concerning blood pressure and body build in similar population groups living in the tropics and subtropics; there have been no studies on blood lipids or electrocardiographic patterns and no autopsy studies. In view of the uncertainty which still exists concerning the relationship between environmental factors (e.g., physical activity, dietary pattern), blood lipids, and coronary athersclerosis, there is clearly a need to investigate fully the possible effects on blood lipids and on coronary heart disease of large muscle activity in persons and groups ingesting diets which, in theory, are potentially atherogenic. This work has been in the nature of a pilot survey, that is, an attempt to assess whether more prolonged and elaborate investigations are warranted either in this particular society or in similar social groups still in existence in Africa. Socioeconomic background of the Sambum. The Samburu are a nomadic NiloHamitic tribe living in the Northern Province of Kenya and dependent entirely on
D.T.M.
Kenya & I$.
their herds of cattle, sheep, and goats for their economy and livelihood; agriculture is completely absent from the society. Every adult male belongs to a particular age set, and the time of his initiation into that age set determines his sub-age set; each of these separate groups has a specific name. The three main groupings are boys, warriors, and elders, and with a detailed knowledge of this social organization it is possible to make a fairly accurate assessment of individual ages. Physical activity. At all age levels there is a fairly high degree of physical activity associated with the herding, watering, and grazing of cattle. Family migrations usually take place every 6 weeks or so; the whole settlement moves about 10 to 1.5 miles, whereas, seasonally, cattle may be driven by the younger men to areas 50 or even 100 miles distant in search of grazing or water. The task of herding the main stock is undertaken by older boys, warriors, and elders, and a day’s herding may involve a trek of up to 20 miles. Warriors and elders who are not herding will assist with watering cattle, and this may involve lifting 400 gallons of water 4 or 5 feet by hand every other day, using only a wooden bucket. Long distances are traveled by the warriors in their wanderings around the countryside, and they may walk 30 miles
From the Department of Medicine, Makerere College Medical School, Kampala, Uganda. This study was made possible by grants from the United States Public Health Service Research Grants Committee, and the East African Council for Medical Research. Received for publication May 18, 1961.
437
(H-4791).
Makerere
College
438
Am. Hcavt I. April, 1962
Shaper
or more a day in the hot sun, for several days in succession. The early years of elderhood are usually harsh and exacting, and as a man grows older his physically active role becomes less marked, although he will spend a considerable amount of time in search of lost cattle or visiting nearby settlements or villages. Diet. The diet consists almost entireI> of milk and meat. Blood is a variable and minimal part of the diet and is used to any extent only during the dry season. Carbohydrates are practically absent from the diet of the warriors and elders, and vegetables are eaten only in very small quantities. The warriors may drink sotne 4.5 to 7 liters of milk at a single sitting, and, during the wet season, when milk is plentiful, they will do this twice a day; the amount will diminish to a total of 2 to 3.5 liters a day or even less in the dry season. Meat may be taken infrequently when tnilk is abundant and once or twice a week in the dry season. The elders drink less milk than do the warriors and take meat more regularly, for unlike the warriors they are under no ritual prohibitions. Serniquantitative assessments indicate a high-fat, high-protein, and low-carbohydrate diet, but there is clearly a marked seasonal variation in intake. The average fat content of several specimens of Samburu milk examined was 5.6 per cent, and, allowing for daily intakes of 3.5 liters for boys and elders and of 7 liters for warriors and young elders when supplies are adequate, this will give daily intakes of 196 and 392 grams of fat, respectively, providing at least 60 per cent of total caloric intake. In regard to the Samburu district as a whole, milk is probabl? abundant for some 4 months of the year, sufficient for needs during an additional 4 months, and insufficient during the remaining 4 months when meat has to be used to supplement the diet. Even though cattle and small stock are, in theory, available to maintain food intakes during periods of inadequacy, cultural patterns are such that animals are not readily slaughtered even in time of need, and imported foodstuffs (e.g., maize meal) are by custom not taken by adult males. Thus, the high-fat, high-protein diet varies quantitatively with the seasonal variations in
supply, and periods of frank famine not unknown in the Samburu territory. Material
and
are
methods
This study was carried out in the Maralal-K’amba area of the Northern Province of Kenya during April, 1960. There had been an exceptionally severe dry period before our visit, but slight rain had fallen in December, 1959, and more rain fell in March and April, 1960. The survey was restricted to males, and, in all, 105 warriors (age range of 16 to 31 years; mean age of 26 years) and 178 elders (age range of 34 to 90 years; mean age of 47 years) were studied. Ages were assessed by Paul Spencer, an anthropologist who had lived for over 3 years as a member of the Samburu tribe. This was clone b\ascertaining the age set and sub-age set df each subject, and the method was considered to be accurate to within 2 years for the majority of subjects. All subjects were weighed and their heights measured. Blood pressures were recorded by one observer” after the subjects had been seated for several minutes with the cuff in position. The lower of two to three readings was recorded and the diastolic pressure was read at the onset of the fourth phase. Electrocardiograms were obtained on 100 subjects (age range of 34 to 90 years; mean age of 48 years), using a direct-writing transistor cardiograph operated by batteries. Tracings were onl) recorded with the subjects at rest, and chest leads were limited to Vz, V4, and Vs positions. The following estimations were carried out on samples of venous blood obtained in the morning: total cholesterol (l), lipid phosphorus (2), triglycerides (3), and total fatty acids (4). Information on diet was compiled from the personal experience of Paul Spencer, and from repeated and detailed enquiries made by mvself during this survey and on earlier visits to the area. No formal survey of diet has been attempted in this nomadic group, but this is to be carried out in the near future by the Kenya government. Results
The majority of the males were on the lean side; the warriors were slender rather
Cardiovascular
studies in Samburu tribe of Northern
than muscular in appearance, and only a few individual elders were observed who could be considered to be overweight. AA 19-year-old male had a congenital heart disorder (probably Fallot’s tetralogy) ; another of the same age had clinical evidence of right ventricular hypertrophy, and still another one, a 31-year-old warrior, had early mitral incompetence with slight left ventricular hypertrophy. No clinical evidence of cardiovascular disease was noted in any of the elders examined, although peripheral arteriosclerosis was not uncommon in the older subjects. Body build and blood pressure. The Samburu are predominantly lightweight individuals, and with increasing age, no increase in average weight is recorded. The mean height for all the males is 68.9 inches (SD. 2.9 inches), and the mean weight of 126.2 pounds (SD. 14.0 pounds) remains remarkably constant in each decade of life from the third onward. The average increase in weight for each inch of increase in height is 1.7 pounds; this is about one third of the increase seen in American males5 Comparison of American and Samburu average weights by age (with due allowance for clothing) shows a difference in mean weight at 20 to 29 years of 25 pounds; this difference increases to 34, 38, and 39 pounds, respectively, in the subsequent three decades and falls slightly to a difference of 35 pounds in the 60 to 69-year period. Almost nine tenths of the Samburu males are less than 90 per cent of American average weights for their height and age. Data on blood pressure in adult male Samburu are given in Table I. The systolic blood pressure is significantly lower than that of Americans” at all ages and shows no increase with increasing age from 20 to 59 years. A rise in systolic pressure is recorded in the over-60 group. Corrected for differences in method, diastolic pressures in the Samburu are lower than those in Americans at all ages and fall significantly in the Samburu after the age of 49 years _ . Levels of plasma lipids. The mean levels and standard deviations of the four lipid components studied and the ratio of cholesterol to phospholipids (C/P) are shown
h-enya
439
by age decades in Table II. When warriors and elders are compared as two separate no statistically significant differgrow, ences can be demonstrated between the mean levels in any of these components,6 although when grouped according to age decades as in Table I I there is a statisticall> significant fall in the 50 to 59 group in both total cholesterol and levels of phospholipids, with corresponding changes in the C/P ratio. The level of cholesterol remains lowered into the over-60 group, whereas the level of phospholipids rises again in this age group. Electrocardiographic j&dings. Electrocardiograms were obtained on 100 elders (age range of 34 to 90 years; mean age of 48 years). No gross cardiovascular disease was noted in any of these elders. Only 3 subjects had an elevated diastolic blood pressure (135/95; 145/100 mm. Hg), but without evidence of left ventricular hypertrophy, and in these 3 subjects the electrocardiogram was normal. Possible ischemic patterns were seen in 2 subjects-one aged 52 years with slight T-wave inversion in several leads, and one aged 81 years with a left bundle branch block. In neither of these two subjects did the tracings show conclusive evidence of myocardial disease. Moderate flattening of T waves without inversion or other significant changes were noted in 7 other subjects. Discussion
Is the rise in systolic and diastolic pressures seen in so many populations a “normal” phenomenon, or is it a reflection of Table 1. Blood pressure by age in adult male Samburu. Afean systolic and diastolic levels and standard deviations .4 ge decades
NUW ber ~
20-29 30-39 40-49 50-59
f-50+ *Diastolic
Syhdic
S.D.
111.5 112.3 112.2 109.2 116.6
10.8 12.3 11.1 10.3 14.1
’
Diasto1ic*
S.D.
76.5 76.7 78.8 74.9 74.8
7.0 8.1 8.1 7.6 7.2
~ 41 79 54 43 22
readings
recorded
as fourth
phase.
440
Am. Heart J. Afiril, 1962
Shafler
Table II. Plasma lipids in adult Samburu males (in milligrams and standard deviations)
per 100 ml. with mean values
Age decades Total 15-19 Number of subjects
1
20-29
1 30-39
1
10-10~~0-59
1
60+
13
52
66
33
27
10
Total cholesterol Mean SD.
164.0 42.6
168.0 39.4
170.0 38.8
168.0 37.9
153.0 33.0
144.0 38.1
166.0 39.2
Phospholipids Mean SD.
208.9 37.9
207.2 37.9
214.5 33.3
226.1 32.2
193.0 29.5
223.4 12.8
212.0 34.5
C/P ratio Mean S.D. Total fatty acids Mean SD. Triglycerides Mean SD.
0.79 0.15
0.83 0.02
0.80 0.11
0.74 0.15
0.79 0.12
0.69 0.12
201
0.79 0.14
243 52.0
256 60.4
2.51 76.9
260 48.3
244 41.9
242 44.9
254 58.1
74.0 7.8
83.5 40.4
86.0 38.6
83.5 7.8
84.0 6.8
97.0 41.9
85.0 31.9
the incidence of hypertension in the communities observed? Studies within East Africa’ indicate that although large increases in blood pressure with age are unusual, significant variations in mean levels of blood pressure and in the relationship of blood pressure to age may occur from one tribal and geographic area to another, whereas a study in West Africa has indicated a close parallel between American and African patterns of blood pressure.8 In a recent review of blood pressure in relation to age and sex in the tropics and subtropics, Lowensteing discussessome 26 references concerned with various ethnic and social groups. He considers that those of the groups reviewed which show no increase in mean blood pressure with age during adult life represent relatively small homogeneous populations living under primitive conditions, more or less undisturbed by their contacts with civilization. The rise in blood pressure seen with age in most of the groups he reviews is, in his opinion, ‘la consequence of civilisation or the process of acculturation.” From a study of Bushmen in the Kalahari, Kaminer and LutzlO
also conclude that a rise in blood pressure is not a characteristic of a normal aging process, and regard it as an indication of the existence of essential hypertension in a community. Our findings in the Samburu would suggest that an increase in weight and a rising blood pressure are not necessary accompaniments of the aging process. The rise in systolic blood pressure seen in the seventh decade in the Samburu is not due to the presence of hypertension in this group and may be a manifestation of decreased elasticity of the aorta and larger blood vessels. The mean level of plasma cholesterol for all Samburu males is comparable to that found, by an earlier study, in healthy adult African males of Kampala, Uganda, who were living on a diet to which fat contributed 10 to 15 per cent of the total calories.ll Most recent investigations into dietary patterns and blood lipids have shown that the customary dietary habits of communities are usually reflected in their mean levels of serum cholesterol, and that increases in the consumption of
Vohme Nwwber
63 4
Cardiovascular
studies in Samburu
animal fat lead to approximately parallel increases in the mean levels of blood cholesterol. In the light of the dietary pattern described in the Samburu tribe, their levels of cholesterol seem to be contrary to this thesis and require explanation. The mean levels of phospholipids, total fatty acids, and triglycerides are also in keeping with levels found in groups on lower fat diets6 Initially, an attempt must be made to answer the question whether differences in habitual physical activity could account for the variations in the concentrations of blood lipids in different populations, and, in particular, whether this factor might be responsible for the unexpectedly low levels of lipids in the Samburu. Reviewing at length the data from many countries, Keys*2 concludes that physical activity does not explain the large differences in concentrations of serum cholesterol observed between populations eating different amounts of fat. This is not to deny the possibility that physical exercise plays some part in regulating the concentration of lipids in the blood, but it does not appear to be a major regulating mechanism. It seems reasonable to suggest that the low levels of blood lipids found in the male Samburu are, in the main, associated with the quantitative variability in their highfat diet, and that their high degree of dynamic physical activity does not by itself account for these findings. The findings on blood lipids in the Samburu would suggest that for a high intake of butter fats or other saturated fats to produce abnormally high levels of lipids in the blood, the intake must be habitual and, probably, must be part of a lifespan pattern of diet. Although the number of Samburu studied by electrocardiography is far too small to allow any conclusive statement to be made concerning the relative frequency of the complication of coronary heart disease, there is at present no autopsy information available from this tribe. All we can suggest at the time of writing is that the complications of coronary atherosclerosis, as evidenced by our electrocardiographic findings, are apparently uncommon in the adult male Samburu. Even though minor changes suggestive of ischemia are noted, it must be remembered that
tribe of Northern
Kenya
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in some parts of Africa there is convincing evidence that electrocardiographic changes which in Europe would be interpreted as indicating ischemic heart disease may be found in a large proportion of healthy subjects.13J4 It is clearly undesirable to rely solely on this relatively small electrocardiographic survey, and supporting pathologic information is being sought. By the accumulation of data concerning peoples who live in special environmental situations and at different levels of “civilization,” studies in geographic pathology, such as the present one, may lead to a better understanding of some of our cardiovascular problems, e.g., essential hypertension and coronary atherosclerosis. Although the urgent requirement is for adequate autopsy material which can be correlated with clinical and biochemical information, this is seldom if ever available in areas such as we have described, and by the time that adequate pathologic facilities are available it may well be that the way of life has been significantly altered as regards dietary habits and patterns of physical activity. It must be emphasized that this has been an uncontrolled pilot study. In order that more definite conclusions may be reached, seasonal studies as well as individual absorption studies are now being carried are being out, and direct comparisons made with other groups in East Africa. The results of these more extensive studies will be reported later. Summary
The Samburu tribe of Northern Kenya live on a diet of milk and meat and are physically very active. There is no increase in weight with age, and only a small increase in weight with advance in height. They show no rise in systolic blood pressure until the seventh decade, and diastolic pressures fall after the fifth decade. Levels of lipids in the blood are comparable with those found in groups living on low-fat diets, and it is suggested that this phenomenon is related to the seasonal variation in supply. Initial electrocardiographic studies suggest a low incidence of coronary heart disease. Further studies are in progress to investigate more fully the many questions raised by this initial survey.
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Am. Heart J. Afiril, 1963
Shaper
The members of this expedition included Professor A. W. Williams, Dr. P. G. Wright, Mr. J. Kyobe, and Mr. P. Spencer. Without their energetic participation this work would not have beenpossible. We wish to thank the District Commissioner. Samburu District, for permission to conduct this survey in the Maralal-Wamba area, and the Department of Physiology for the use of their mobile laboratory (Wellcome Trust). REFERENCES 1. Abell, L. L., Levy, B. B., Brodie, B. B., and Kendall, F. E.: A simplified method for the estimation of total cholesterol in serum and demonstration of its specificity, J. Biol. Chem. 195:357, 1952. 2. Bartlett, G. R.: Phosphorus assay in column chromatography. Modification of Fiske and Subba Row method. 1. Biol. Chem. 234:466. 1959. 3. Van Handel, E., and Zilversmit, D. B.: Micromethod for determination of serum triglycerides, J. Lab. & Clin. Med. 50:152, 1957. 4. Stern. I.. and Shaoiro. B.: A raoid and simole method ‘for the -determination’ of esterihed fatty acids and for total fatty acids in blood, J. Chn. Path. 6:158, 1953. 5. Shaper, A. G., Williams, 4. U’., and Spencer, ”
P. : Blood pressure and body build in an African tribe living on a diet of milk and meat, East African M. J., 1962 (in press). 6. Shaper, A. G., Jones, M., and Kyobe, J.: Plasma lipids in an African tribe living on a diet of milk and meat, Lancet 2:1324, 1961. 7. Williams, A. W.: To be published. 8. Abrahams, D. G., Alele, C. A., and Barnard, B. G.: The systemic blood-pressure in a rural West African community, West -4frican M. J. 9:4.5, 1960. 9. Lowenstein, F. W.: Blood pressure in relation to age and sex in the tropics and subtropics, Lancet 1:389, 1961. 10. Kaminer, B., and Lutz, W. P. W.: Blood pressure in Bushmen in the Kalahari desert, Circulation 22:289, 1960. 11. Shaper, A. G., and Jones, K. W.: Serum cholesterol, diet and coronary heart disease in Africans and Asians in Uganda, Lancet 2:534, 1959. 12. Keys, A.: Diet and the epidemiology of coronary heart disease, J.A.M.A. 164:1912, 1957. 13. Grusin, H.: Peculiarities of the African’s electrocardiogram and the changes observed in serial studies, Circulation 9:860, 1954. 14. Powell, S. J.: Unexplained electrocardiograms in the African, Brit. Heart J. 21:263, 1959.