Blood pressures of !Kung bushmen in Northern Botswana

Clinical communications

Blood pressures of !Kung bushmen

in Northern Botswana

il. S. TI~~swc~~, M.B., Ch.B., M.D., M.K.C’.I’. N. M. k-cmelly, M.B., Ch.B., Ph.D., M.R. C.I’. J. D. L. Hansen, MB., Ch.B., M.D., F.X.C.P., D.C.11. Ii. B. Lee,” M.A., Ph.D.

Cupe Town. and Johamesburg, South Africtr, und Cumnbridge, Mms.

A bout a dozen groups of people in the world do not show the rise of blood

pressure with increasing age that is the average pattern in developed countries. These groups have nearly all been found in remote parts of the world (Table I). But the observations that can be made on these communities, far from medical school labo- ratories, are not only of anthropological interest; they may also contribute to our understanding of the nature and causes of essential hypertension. The normotensive community we describe here has not been reported hitherto in the medical literature except for our preliminary communications.1-3

Subjects and methods

We report here some of our investiga- tions among bushmen of the !Kung tribe4 in northwestern Ngamiland, Botswana, near the Aha Hills. The 800 bushmen in this arca have been kept isolated by a surrounding waterless zone 60 to 100 miles

wide.5 They live as independent a life as any bushman group in existence today. Many of them still live all the year round as hunter-gatherers.‘j

I. DeVore and R. B. Lee of the Depart- ment of Social Relations, Harvard Univers- ity, set up a camp next to the bushman camp near the Dobe waterhole in 1963. Since then except for the period 196.5-6, the Harvard group has had one to three anthropologists living in the area, usually for periods of about 2 years. The resident scientists have learnt the !Kung language, got to know the people, and each has stud- ied a different aspect of bushman life, taking pains, however, to disturb it as little as possible. Specialists have been brought to the camp from time to time for short visits, which have been fruitful because the visitors have been able to base their studies on the resident scientists’ personal knowl- edge and understanding of the bushmen.

The bushmen live in camps of 20 or more people, the basis of which is an ex-

6 Truswell et id.

T&c I. Communities in which blood pressure does not rise with (lgc

tended family group. Each camp is associated with a waterhole. Lee6 has found that about 70 per cent of food by lveight is vegetable, collected by the women. A variety of nuts, fruits, roots, bulbs, and leaves are available, varying with the season. The most important food is the nut of the mongongo (manketti) tree (Ricinodendron rautenenii) because it is abundant, keeps well, and is rich in protein and fat.’ Aleat is provided by some of the men, who hunt with poisoned arrows.

The bushmen have only a few basic possessions, which they carry with them when they move; they are therefore able to travel light. Individuals move freely be- txveen camps and the camps move aljout five times a year. During and after the wet season (November to March) there are pans of seasonal water out in the l~usli so that the bushmen can camp beside then1 and collect food in the surrounding area. But as the pans dry up the bushmen return to the permanent water-holes; at the end of the dry season they have to walk increasing distances to find food. Some of the bushmen obtain milk occasionally from Bantu (Herero and Ts\vann) pastoralists who have settled in the ;lre;t in the last 4.5 Jrears. A fen, 1~1shmen \\.orl< for the 13antl1 as Iterds- men part of the year. The bushmen have no

alcohol but they smoke tobacco. They have very little salt. There are no deposits of salt in the area and the principal means of obtaining salt is to walk to Tsumkwe, 30 miles away in South West Africa, where the Administration has established a set- tlement for the !Kung bushmen on the South West African side of the border.

The medical team made 3 Irisits to the llarvard camp; each trip included 10 days’ \vork in the field. The first visit lvas made in October, 1967, at the end of the dry season, when it jvas hot and dry and food was scarce. The second visit was in April- Slay, 1968, after the rains. During tllat \.isit it was warm in the clay and cool at night; there were occasional pans of stand- ing water in the area and some of the I~ushmen showed signs of malaria. The third Irisit \vas made in July, 1969, halfway through the dry season. Tl~ougl~ the nights \vere cold, the days were sunny and quite \varm out of the wind. There \vas adequate food.

The bushmen were seen in family groups. Babies, pregnant women, the sick, and the aged were all included in our first two visits. A ljricf history was taken through ;tn interpreter and ~1~11 individual \v:~s examined with tlic siil,jec( ll.ilig clo\\n. 111 the third visit we examined only adults, fol-

l’uble II. Mean blood pressures of bushmen in cage nnd sex subgroups

?/let1 120/75 124/75 m/75 116/75 118/72 113/67 117/66 (II) (3) (16) (19) (17) (14) (6) (4) (79)

liTomen 114/72 1 IA/73 113/73 116/71 123/76 130/72 123/68 - (II) (5) (17) (13) (17) (9) (8) (4) (73)

Both sexes 117/73.5 119/74 116.5/74 116/74.5 lSO.5/74 1?1.5/69.5 1 LO/67 (11) (8) (33) (32) (34) (23) (1-l) (8) (Si)

Mean* for both sexes 88.0 89.0 88.2 88.3 89.5 86.8 84.7

systolic - diastolic *Ihstolic f ___~__ .

3

~:hom we also recorded electrocardiograms (ECG’S).~ The ages of the bushmen have been carefully worked out using rank order- ing and relating this to known historical events in the neighborhood. The statisti- cal technique for age determination was developed by Dr. Nancy Howell-Lee, the demographer on the Harvard expedition and now at the Office of Population Re- search, Princeton, N.J. The bushmen living within 10 miles of Dobe were brought to the base camp by truck for the examination. Any who were ill were treated. To examine the bushmen at the extreme east of the area (i\lahopa and Goshi) and all those living south of the Aha Hills, (Xai Sai and Xoxgana) we took our equipment \vith us and drove to the bushman camps.

Blood pressures were measured with the same mercury sphygmomanometer (Baum- anometer) throughout, usually by Dr. Trus- iveIl. They were taken in the right arm with a cuff measuring 13 by 24 cm. During the first two visits most of the subjects were examined on an improvised examination couch inside the medical tent where it was a little cooler than out in the sun. On the third visit the people were examined on a camp stretcher outside in the sun, \vith the truck drawn up to provide shelter from the wind. Conditions were unhurried and we tried to help the subjects feel relaxed. Blood pressures mere measured during the course of a full medical examination and the subjec.t was l>.ing do\vn \vith his fatnil> sitting nearljy.

Twenty-four hour urine specimens \vere

collected from 6 bushmen living at Dobe and from 2 controls (ourselves) in 1967 and from 4 of the same bushmen and from 3 controls in 1968. On each occasion the urines were collected on the eve of our return journey. Aliquots (preserved with iodine in 1967 and with oxalic acid in 1968) were carried back with us by jeep and plane in a cool box and frozen as soon as we ar- rived in Cape Town.

Urinary sodium and potassium were measured by flame photometry with lith- ium as internal standard, and chloride \vas measured by potentiometric titration in an Aminco chloride titrator. Creatinine ~-as measured with alkaline picrate and nitrogen by Kjeldahl.

Results

Blood pressures were measured in a total of 152 bushmen aged 1.5 to 83 years. The study group was composed of 79 men and 73 women. hleasurements in 22 bushmen were taken on each of our 3 visits; another 22 subjects were measured on 2 of the 3 visits. The remaining 108 bushmen were examined only once. For each bushman we used all the available measurements to obtain a best estimate of blood pressure, which was therefore based on 2 or 3 re- peated measurements at different seasons in 44 of the subjects and on a single measurement in the rest (108 subjects). The individual I jlood pressure values were grouped by sex and decade and the mean values of the 14 sul)groups are shown in Table II.

Am. Heart I. J&y, 1972

In male bushmen systolic and diastolic pressures both showed a slight but defi- nite downward trend with increasing age throughout adult life. In the women the line joining decade mean systolic pressures rose by about 10 mm. Hg to a higher step in the second half of life. But their diastolic pressures stayed the same until the two oldest age groups, in which there was a slight drop.

Combining the values for men and women (unweighted mean values in the third row of Table II), systolic pressures were about 3 mm. higher in people over 49 years of age while diastolic pressures fell after the age of 59. Pulse pressures were 42 to 45 mm. from ages 15 to 49 years and 52 to 53 mm. from ages 60 to 83 years. These trends are illustrated in Fig. 1, against the curve of London blood pressures taken by Hamilton and associates9 (1954) which is typical of Western, developed communities. The mean blood pressures (diastolic + x pulse pressure) for men and women combined condense all the results into a row of single figures at the bottom of Table II. They show a remarkable constancy despite increasing age.

In the 22 bushmen who were examined on all three visits, the mean blood pressures were:

October, April-May, July, 1967 1968 1969

117/73 126/75 11 l/64

The difference cannot be explained by ob- server variation; nearly all were taken by A.S.T. The lower readings at the July (winter) visit were unexpected. On this occasion, subjects were examined outside in the winter sunshine and it is possible that they were more relaxed than when they were examined on their own inside the doctors’ tent on the two earlier visits.

Table III shows the arm circumferences of the bushmen, arranged by sex and age. The measurements were taken midway l)et\v.crn the rigllt ell)ow antI sl~ouldc~r in about Ilalf Ll~c. slll)jt.c.ls \\,IIosc: I,lootl 1)1-c+ surcs \vcre recorded. T11c arm circtlnlftxr- ences were at the lower end of the range in Western adults.‘0n’1 In both sexes they

I80

170

160

6C

MALES I _.

H BUSHMEN ,,.- I

-.... LONDONERS i

-,-,-,-,-,-- 1 -.-L-,-,-,-1- g-t+-

25 35 45 55 65 75 25 35 45 55 65 75

AGE Cur)

Fig. 1. Bushmen’s blood pressures with age, compared with standard figures for a group from London (Hamilton and associatess).

were a little higher between 30 to 49 years of age and a little lower in the very young and the very old.

Almost all the bushmen examined were lean, of delicate build, and rather short. Taking all ages together, the men averaged 48 Kg. (106 lb.) in weight (unclothed) and were 161 cm. (5 ft., 3 in.) tall (without shoes). At this height the “desirable” weight for small-framed men is 53.5 to 57.2 Kg. (118 to 126 lb.) in the U.S.A.12 The women’s mean height and weight were 1.50 cm. (4 ft., 11 in.) tall (without shoes) and 40 Kg. (88 lb.) (unclothed), compared with a “desirable” weight range of 44.9 to 48.5 Kg. (99 to 107 lb.) for small- framed women of the same height in the United States. Unfortunately, these “desirable” weights are quoted for people wearing indoor clothes, which might weigh 1 to 2.25 Kg. The triceps skinfolds averaged 5.0 mm. in the bushmen and 9.4 mm. in the women.

To see if there were any changes in weight with age in the two sexes, weight! height ratios (metric) are shown in Table IV together with ratios calculated from average U.S. weights.12 All bushman values were low and there was little change with age except below the age of 20 and over 11itx ngc of 69 years. For coliip;irison, tll(l \\~c*iglll/liciglil intltx (,I yo11ng f2mrric.:ln 111tw was 3X.S, nntl it fell 10 29.5 in III(* same men after 6 Inonths scnli-starv;\tiolI with the loss of 25 per cent of their body

(;fiiYsj ( 15-19 1 20-29 ( 30-39 ~ JO-49 ~ 50.59 ~ 60.69 ~ 70.83

Men 19.7 22.0 23.5 24.2 22.1 22.2 17.8

(4 (3) (11) (11) (6) (7) (4) (3) A:omen 18.4 20.2 21.4 21.4 19.0 21.8 16.6

(4 (4) (10) (5) (7) (3) (4) (3)

Tuble IV. Weight/height ratios for bushen computed with ratios cnlcdtrted from rrvrrclge U.S. weights*

Age 1 15-19 / 20-29 1 30-39 1 40-49 i 50-59 i 60.69 1 70-c%‘.? (-wars)

Uushment Men 24.2 30.0 30.4 31.1 28.8 30.1 21.2 LVomen 24.0 27.5 26.4 27.0 27.1 26.1 21.7

Average U.S.1z hlen$ 34.0 38.7 40.4 41.3 41.6 40.7 - Women 31.6 33.1 36.0 38.1 38.9 39.3 -

*Ratios were calculated from the following formula: 100 x weight (Kg.)

heieht (cm.) tNurnbers of bushmen in each cell were the fame as in Table II. Kalculated for men in shoes 5 ft. 4 in. in height and women in shoes 5 ft. 1 in. in height.

weight, as observed in the Minnesota ex- periment.13

In the 24 hour urine specimens (Table \T), the striking findings both in 1967 and 1968 were the low sodium and chloride content in the bushmen. Sodium and chloride excretions of 30 mEq. per day each would correspond to an NaCl intake of only 2 Gm. per day. The creatinine excretions look rather low in one or two of the bushman urine specimens, suggesting that the collections were incomplete. How- ever, the bushmen were smaller and weighed less than the controls. When the creatinines are expressed per kilogram of body weight, the bushman creatinines come to 83 per cent of the controls in 1967 and 86 per cent in 1968. Potassium, nitrogen, and magnesium excretions were not lower in the bushmen than in the controls.

Discussion

There have been two previous observations of blood pressures in other groups

of southern African bushmen. Bronte- Stewart and colleagues14 mentioned mean values of 119/74 in men and mean values of 110/71 in women in northern South West Africa. Pressures were only taken in 44 subjects and old people were probal)ly under-represented. Kaminer and LutzI measured blood pressures in 99 nomadic bushmen belonging to the Central Group of tribes, living in the area south of Ghanzi, Botswana. The readings did not increase with age and none exceeded 140/90. Two complete bands of people were examined but ages could only be estimated by physi- cal appearance.

We have confirmed these findings in a larger group of separate bushmen whose ages have been worked out with a fair degree of accuracy. There are different de- grees to which populations can deviate from the standard Western blood pressure pattern exemplified by the curves for Lon- don, presented in Fig. 1. Maddocksl’j has introduced a useful classification. In the Type I pattern, mean systolic pressure

y-uljle V. Jjelln vcllue.s (trnd rclnges) OJ’ ZJ hour urimry sodium tend other constituents in hshmen clnd controls

Subjects Creatinize (Gm.lday)

Bushmen 1967 G 0.84 (0.56-1.40) 31 (8-48) 30 (7-77) 70 (31-93) 10.4 (5314.9) 7.4 (6.3-9.6) 1968 4 0.98 (0.54-1.41) 29 (2-64) 36 (5-70) 103 (48-168) 10.6 (5.517.83

Controls 1967 2 1.36 (1.29 & 1.42) 212(179&245) 173 (132 & 215) 68 (52 & 84) 5.7 (6.4 & 11.0) 3.2 (2.1 & 4.2) 196s 3 1.42 (1.23-1.64) 147 (96-172) 121 (62-154) 61 (43-75) 11.4 (10.1-13.1)

rises considerably with age and diastolic pressure rises moderately. In the Type II pattern, systolic pressure rises moderately but diastolic pressure does not rise. In the Type III pattern, systolic and diastolic pressures both stay at the same low level throughout life, and in the Type IV pattern both systolic and diastolic blood pressures decline with advancing age. Accord- ing to Maddocks’ classification, the !Kung bushman males have a Type IV pattern and the women a Type II pattern. When the two sexes and the diastolic and systolic pressures are combined, the resulting mean blood pressures do not change with increasing age.

There are five possible explanations for the bushmen’s immunity from hypertension: (1) low salt intake, (2) lack of obesity, (3) associated illnesses, (4) freedom from the stresses of civiliza- tion, and (5) high magnesium intakes. Taking them in reverse order, Versterr7 speculated that the relatively high serum magnesiums found in some central Kalahari I~ushmenl” might be connected with their freedom from hypertension. However, these sera were not separated from red cells for about 2 days and neither BernsteinI nor we (Table V) found high urinary magnesiums in bushmen.

There is no doubt that in some communities hypertension has appeared with “ac- culturation.“rg~‘” But mental stress is only one of the changes that occur and it is the most difficult to quantify.” Some isolated and peaceful communities have hypertension,22-z4 although one lvould imagine they are not very stressful to live in.

Tropical splenon~egaly25~2G and chronic chest diseasez6 have been associated with low.er I)lood pressures than in the healthier

members of the same communities. A minority of the bushmen had splenomegaly but the spleens were usually not very large and appeared after the wet season, i.e., in April, 1968, when we found blood pressures to be rather higher than at our other visits. Some of the older bushmen showed evi- dence of chronic bronchitis, but most of them appeared healthy on clinical examination. We would not think that chronic infections play more than a minor part in keeping blood pressures 101~. AIaddocks and Vine?” reached the same conclusion in New Guinea.

The bushmen have thin arms and small amounts of adipose tissue. Pickering, Roberts, and Sowry”’ calculated that to obtain the true direct blood pressure, correction should be made for arm girth. Ac- cording to the table in their article, 10 mm. Hg should be added to the bushmen’s indirect systolic pressures and no correction should L)e made to the diastolic pressures. This vvould not explain the absence of hi,- pertension with increasing age, because the bushmen’s arm circumference stayed about the same throughout life. More recent workers have found that the effect of arm girth per se is very smal111~27 and that adiposity has a much closer association. The bushmen have unusually small amounts of adipose tissue and (Table IV) show no “middle-aged spread.” Some of the other communities in Table I remain thin throughout life.

Lastly, our findings are consistent with Dahl’s hypothesis2* that populations ha- bitually consuming less than 5 Gm. of salt a day are relatively free of hypertension. Some more recent between-population com- parisonszg are also in keeping with this hypothesis. Even if salt intake does not

determine which individuals become hyper- tensive within a developed community, the bushmen appear to eat a “low salt diet” which provides little more sodium than was used to treclt essential hypertension”” before oral diuretics became available.

Summary

Blood pressures have been measured, and sociological, anthropometric, medical, and biochemical examinations have been made in an isolated group of !Kung bushmen in northern Botswana.

Blood pressures were taken in 152 bushmen of both sexes, aged 15 to 83 years, who \vere examined in family groups. Systolic and diastolic pressures declined with increasing age in the men. The women showed a small rise of systolic pressure after the menopause but their diastolic pressure decreased slightly with age. The mean blood pressure (diastolic + ?d pulse pressure) for men and women combined thus remained the same throughout life.

Other communities whose blood pressures do not increase with age are reviewed. Of the possible explanations in the bushmen, a low salt intake and a lack of obesity appeared to be important, with relative freedom from mental stress an additional imponderable factor.

\I:e want to thank Professors I. DeVore, V. Schrire, and J. E. Kench and Drs. Nancy Howell- I,ee, Henry Harpending, Patricia Diaper, and John E. Yellen for their help in this work.

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REFERENCES

Truswell, A. S., and Hansen, J. D. I<.: Medical and nutritional studies of !Kung bushmen in north-west Botswana: a preliminary report, S. Afr. Med. J. 42:1338, 1968. Truswell, .A. S., and Hansen, J. D. I..: Serum- lipids in bushmen, Lancet II:684, 1968. Truswell, A. S., Hansen, J. D. L., Wannenburg, I’., and Sellmeyer, E.: Nutritional status of adult bushmen in the Northern Kalahari, Bots- wana, S. Aft-. Med. J. 43:1157, 1969. Thomas, E. 1I.: The harmless people, Iondon, 1959, Seeker & \Varburg. Lee, 1~. B.: The subsistence ecoloav of !Kung bushmen, Ph.1). dissertation, Berkeley, Calif:, 1965. ITniversitv of California. Lee, ‘R. B.: i “W-hat hunters do for a living, or, How to make out on scarce resources,” in Lee, 1~. B.. and I)eVore. I.: Man the Hunter, Chi- cago, ‘1968, Aldine Publishing Company, 1,. 30. Wehmeyer, rl. S., Lee, R. B., and 1Vhiting, RI.: The nutrient composition and dietary im-

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portance of some vegetable foods eaten by the !Kung bushmen, S. Afr. Med. J. 43:1529, 1969. Kennelly, B. M., Truswell, A. S., and Schrire, V.: A clinical and electrocardiographic study of !Kung bushmen, Cardiovasc. Res..Abstracts of the \‘I W’orld Contrress of Cardioloev. Londotr 6-11 September, 1970, p. 185.

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Hamilton, RI., Pickering, G. IV., Roberts, J. A. F., and Sowry, G. S. C.: The aetiology af essential hypertension. 1. The arterial pressure in the Feneral population, Clin. Sci. 13:11, 1954. Pickermg, G. \I’., Roberts, J. A. F., and Sowry, G. S. C.: The aetiology of essential hypertension. 3. The effect of correcting for arm cirrum- ference on the growth rate of arterial pressure with age, Clin. Sci. 13:267, 1954. Karvonen, M. J., Telivuo, L. J., and Jarvinen, E. J. K.: Sphygmomanometer cuff size and the accuracy of -indirect measurement of blood messme. Am. I. Cardiol. 13:688. 1964. I)ocuntenta Geigy Scientihc Tables, 6th Ed., IXem, Ii., editor, Basel, 1962, Geigy, 1’1’. 623- 624. Keys, A., Brozek, J., Henschel, A., hIickelsen, O., and Taylor, H. I,.: The biology of human starvation, Vol. 1, Minneapolis, 1950, I’niver- sity of Rlinnesota Press, p. 146. Bronte-Stewart, B., Budtz-Olsen, 0. E., Hick- ley, J. M., and Brock, 1. F.: The health and nutritional status of the !Kunl: bushmen of South West Africa. S. Aft-. T. Lab. Clin. Med. 6:187, 1960. " Kaminer, B., and Lutz, W. I’. I\‘.: Blood pressure in bushmen of the Kalnhari Desert, Circu- lation 22~289, 1960. Maddocks, I.: Dietary factors in the genesis of hypertension, in Mills, C. I;., and Passmore, Ii., editors: Proceedi,ngs of the 6th International Congress of Nutrttton, Edinburgh, 1964, E. & S. I.ivingstone, I.td., p. 137. Verster, F.: hlagnesium en die Kardiovaskttlere stelsel, Geneeskunde 3:263, 1961. Bernstein, 1~. E.: Blood electrolytes in a bushman Kroup, Proc. Nutr. Sot. S. Afr. 2:56, 1961. Lowenstein. F. \I’.: Blood uressure in relation to age and sex in the Tro&s and Subtrolncs. i\ review of the literature and an investigation in two tribes of Brazil Indians, Iancet 1:389, 1961. Cruz-Coke, Ii., Etcheverry, Ii., and Angel, Ii.: I nlluence of migration on blood-pressure of Easter Islanders, L,ancet 7:697, 1961. Scotch, N. A., and Geiger, H. J.: The epidemiology of essential hypertension. II. Psychologic and soriocultural factors in etiology, J. Chronic IXs. 16:1183, 1963. Hawthorne, V. M., Gillis, C. II., Iorimer, A. It., Calvert, F. R., and \\‘alker, 7‘. J.: Blood lnes- sure in a Scottish island community, Br. Med. J. 4:651, 1969. Xbrahams, 1~. G., Alele, C. A., and Barnard, 13. G.: The systemic blood pressure in a rural [Vest African community, WT. Afr. Med. J. 9:-E, 1960. Miller, I). C., Spencer, S. S., and White, P. D.: Survey of cardiovascular disease among :\fri-

12 T?%swe11 et ill. .‘I >n. IIcurt 1. July, 1972

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cans in the vicinity of the Albert Schweitzer Hospital in 1960, Am. J. Cardiol. 10:432, 1962. Burns-Cox, C. J., and Maclean, J. D.: Spleno- megaly and blood pressure in an Orang Asli community in I4’est Malaysia, AX HEART J. 80:718, 1970. Maddocks, I., and Vine, A. P.: The infiuence of chronic infection on blood pressure in New Guinea males, Lancet II:262, 1966. Kannel, W. B., Brand, N., Skinner, J. J., Jr., Dawber, T. R., and McNamara, I’. M.: The relation of adiposity to blood pressure and development of hypertension, Ann. Intern. Med. 67:48, 1967. Dahl, L. K.: Possible role of chronic excess salt consumption in the pathogenesis of essential hypertension, Am. J. Cardiol. 8:.571, 1961. Evans, 1. G., and Rose, G.: Hypertension, Br. Med. Bill. 27:37, 1971. - Chanman. C. B.. and Gibbons. T. B.: The diet and ‘hypektension: A review, ‘Medicine 29:29, 1950.

ADDITIONAL REFERENCES FOR TABLE I

Donnison, C. P.: Blood pressure in the African native, Lancet 1:6, 1929. Williams, A. W.: The blood pressure of Africans, E. Afr. Med. 1. 18:109, 1941. Murrill, R. I. i A blood pressure study of the natives of Ponaoe Island. Eastern Carolines. Hum. Biol. 21:47, 1949. 21:47, 1949. Murphy, W.: Some observations on blood pressures Murphy, W.: Some observations on blood pressures in humid tropics, N. Z. Med. J. 54:64, 1955. in humid tropics, N. Z. Med. J. 54:64, 1955. Hunter, J. D.: Diet, body build, blood pressure and Hunter, J. D.: Diet, body build, blood pressure and serum cholesterol levels in coconut-eating Poly- serum cholesterol levels in coconut-eating Poly- nesians, Fed. Proc. 21(4) part 2:36, 1962. nesians, Fed. Proc. 21(4) part 2:36, 1962.

Prior, I. A. M., Evans, J. G., Harvey, H. P. B., Davidson, F., and Lindsey, M.: Sodium intake and blood pressure in two Polynesian populations, New Engl. J. Med. 279:515, 1968. Ethiopia, 1958. Nutrition Survey: A Report by the Interdepartmental Committee on Nutrition for National Defense (ICNND), LVashington, D. C., September, 1959, U. S. Government Printing Office. Whyte, H. nI.: Body fat and blood pressure of natives in New Guinea: Reflections on essential hypertension, Australas. Ann. Med. 7:36, 1958. Maddocks, I., and Rovin, L.: A New Guinea population in which blood pressure appears to fall as age advances, Papua New Guinea Med. J. 8:17, 1965. Maddocks, I.: Blood pressure in Melanesians, h4ed. J. Aust. 1:1123, 1967. Padmavati, S., and Gupta, S.: Blood pressure studies in rural and urban groups in Delhi, Circulation 19:395, 1959. Maddocks, I.: Possible absence of essential hypcr- tension in two complete Pacific Island populations, Lancet lI:396, 1961. Shaper, A. G., Williams, A. W., and Spencer, P.: Blood pressure and body build in an African tribe livinp- on a diet of milk and meat, E. Afr. Med. T. 38569, 1961. Shaper, A. G.: Blood pressure studies in East Africa, in Stamler. T.. Stamler. R.. and Pullman. T. N..

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editors: The epidemiology of hypertension, New York and I.ondon, 1967, Grune & Stratton, Inc., p. 139. Mann, G. V., Shaffer, R. D., Anderson, R. S., and Sandstead, H. II.: Cardiovascular disease in the hlasai, J. Atheroscler. Res. 4:289, 1964.

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Blood pressures of !Kung bushmen in Northern Botswana