Antecedents of Cardiovascular Disease in Six

Solomon Islands SocietiesBy LOT B. PAGE, M.D., ALBERT DAMON, PH. D., M.D.,

AND ROBERT C. MOELLERING, JR., M.D.

SUMMARYCardiovascular risk factors have been analyzed as part of a combined ethnographic, anthropometric, and

medical study of 1390 adult subjects in defined populations representing six Solomon Islands Societies. Thesix societies, all at low levels of acculturation, differed in habitat, way of life, and exposure to Westerncivilization. Criteria for ranking the societies in respect to acculturation were developed based on

demographic changes within defined populations, secular increase in adult height, length and intensity ofcontact with Western cultural influences, religious belief, education, availability of medical care, economy,and diet. The six tribal groups were ranked by these criteria as follows: (1) Nasioi, (2) Nagovisi, (3) Lau, (4)Baegu, (5) Aita, (6) Kwaio. Physical health and nutrition were good in all six groups, and clinical evidence ofcoronary heart disease and atherosclerosis was absent. Serum cholesterol levels were higher at almost allages and both sexes in the three more acculturated than in the three less acculturated groups. Serum uricacid levels were lower in the more acculturated than in the less acculturated groups. Among adult males inall groups, systolic blood pressure showed no age-related trend while diastolic blood pressure declined withage in the three less acculturated groups. Among adult females systolic blood pressure increasedsignificantly with age in the three more acculturated groups but showed no age trend in the less ac-

culturated. Weight declined with age in all groups. Analysis of electrocardiograms by the Blackburn methodshowed striking absence of codable abnormalities in all groups and a lower frequency of most abnormalitiesassociated with coronary disease than in any population previously reported.The differences in serum cholesterol and uric acid levels, and in intrapopulation trends of blood pressure

in relation to age between the more and less acculturated groups were found to correlate best with dietarydifferences, especially in intake of salt, and of tinned meat and fish. The biologic differences noted may

represent the earliest antecedents of cardiovascular disease in these societies.

Additional Indexing Words:Salt intakeBlood pressureCholesterol

AtherosclerosisDiet

Uric acid

Risk factorsAcculturation effects

Epidemiology

W7 HILE THE OCCURRENCE of atheroscleroticcardiovascular disease is worldwide in distribu-

tion, a number of societies have been described inwhich both the manifestations of atherosclerosis andits known antecedents appear to be strikingly absent.Examples of such societies include Melanesian tribesin New Guinea,' Polynesian residents of isolated

From the Peabody Museum and the Department ofAnthropology, Harvard University and the Departments ofMedicine. Tufts University School of Medicine, Newton-WellesleyHospital, Harvard Medical School and the Massachusetts GeneralHospital.

Supported by Grant No. GM-13482, National Institutes ofHealth.One of the authors, Dr. Damon, died before publication of this

study.Address for reprints: Dr. Lot B. Page, 2000 Washington Street,

Newton Lower Falls, Massachusetts 02162.Received December 13, 1973; revision accepted for publication

February 28, 1974.

1132

islands in the Fiji,2 Cook,3 and Caroline4 groups,Kalahari Bushmen,5 Congo pygmies,6 Nomadic tribesin East Africa,7 certain South American Indians,8 andAustralian Aborigines.9 Where comparisons have beenmade between these primitive peoples and towndwelling natives of similar origin who have beenassimilated into the way of life of Western civilization,-the town dwellers frequently exhibit the familiar riskfactors for atherosclerotic disease such as elevatedarterial pressure and rising blood lipids." 0, , 12, 13

The process of acculturation thus seems to lead to theappearance of these. risk factors. Many different in-fluences have been suspected in their emergence.They include changes in diet,3 changing ethical,social, and moral values,'4 crowding,5 anxietyengendered by entry into a differently orientedsociety, economic stress, competition, racial andethnic tensions, noise, pollution, pace of life, etc.14 15

In most reported studies, the multiplicity ofsimultaneous forces acting on acculturating societies

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CARDIOVASCULAR DISEASE IN TRIBAL SOCIETIES

makes it difficult to assess the importance of any in-dividual influence.The study reported here is an attempt to locate the

earliest antecedents of cardiovascular disease inseveral Melanesian societies still living in traditionalrural tribal groups, but beginning to change in differ-ing ways and degrees in response to Western culturalinfluences.

Design of Study

The over-all purpose and design of the HarvardSolomon Islands Project have been described in detailelsewhere. 6, 17 Its goal is to examine interrelationshipsamong culture, environment, human biology, and dis-ease patterns in a variety of populations that differ inhabitat, way of life, and exposure to Western civiliza-tion.

For each population selected for study, a culturalanthropologist first obtained detailed ethnographicdata during a residence of 18 to 24 months with thegroup. Data so acquired, largely through the locallanguage, included dietary, cultural, economic anddemographic information, the establishment ofbiologic kinship and estimation of ages. No writtenbirth records existed for most of the subjects. Ages es-

timated by painstaking "triangulation" against knowndates are deemed by our ethnographers to be accurateto within two years for children and five years foradults. At the completion of his own research, theethnographer remained or returned to assist in thebiomedical survey.

The biomedical team was composed of sixphysicians (three internists, an ophthalmologist, a

pediatrician, and a radiologist), a dentist, and fivebiological anthropologists. Four to six weeks were

spent examining each group, in assembly-line fashion,using buildings of native construction, designed andbuilt for the purpose and centrally located in the tribalarea. Twenty-five to thirty-five subjects were ex-

amined a day, by families. The protocol includeddetailed anthropometric measurements, geneticobservations, and somatotype photographs, physicaland ophthalmological examinations, dental examina-tion with casts of the teeth, a standard 12-lead elec-trocardiogram and a postero-anterior chest film. Bloodsamples were drawn for determination of hemoglobin,complete blood typing, malaria smears, cholesterol,uric acid, and antibodies. Except where tribal taboosprevented it, urine and stool samples were obtained,and in some subjects samples of hair, nails, and biop-sies of skin were obtained. After other examinationswere completed, intradermal tests for histoplasrnosis,M. tuberculosis, and the "atypical" mycobacteriawere implanted and read 48 hours later.

Circulation. Volurne XLIX, June 1974

Methods

All physical examinations and blood pressure

determinations on subjects aged 15 years and older were

performed by a single observer (LBP) using a mercury

manometer on the right arm, with the subject seated com-

fortably on a bench. A small percentage of observationswere made with a recently calibrated aneroid manometer.Two or more independent readings were averaged. Inanalyzing diastolic pressures, phase IV of the Korotkoffsounds was used.

Blood samples drawn into vacutainers were centrifugedwithin an hour; serum was separated promptly and held at 5to 10GC for periods up to seven days before being shippedon ice to the laboratory. Cholesterol and uric acid deter-minations were performed on all samples by a singlelaboratory using methods", 19 which remained unchangedthroughout the study.*

All the anthropometric measurements reported here were

taken by one observer (AD). Standard 12-lead electrocar-diograms were obtained on most subjects aged 15 years andolder, using a Sanborn Visette instrument. The electrocar-diograms were interpreted (RCM) and were coded by themethod of Blackburn et al.`0

Study Subjects

In all, 2586 persons, including 1390 adults aged 15 years

and over in six different tribal societies were examined. Thestudy groups were defined residentially, and effort was madeto obtain the voluntary cooperation of 100% of residents inthe designated hamlets. Participants received payment, ingoods or cash, for time lost from their normal work. Medicaland dental treatment were offered to all, regardless of par-

ticipation.Three of the societies lived on the island of Bougainville,

Territory of Papua and New Guinea, and three on the islandof Malaita, British Solomon Islands Protectorate (see map,

fig. 1.). Both islands, lying from 50 to 70 south of theequator, are volcanic in origin and tropical in climate withvear-round temperatures averaging 70 to 850F, and withhigh annual rainfall.

Bougainville's coastal plain has been settled by a smallpopulation of Europeans since 1885. The island saw heavyfighting during World War II, and was occupied at varioustimes by both Japanese and American forces. After the war,

the European census declined, remaining above the prewarfigures,2' and has increased markedly with the developmentof a large copper mine since 1968.

Malaita was never occupied during World War II. Euro-pean settlement has been and remains small. The nativepopulation, scattered among the hills and along the coast,was estimated at something over 50,000 in 1970.22 Few

Europeans have visited the interior of the island.

Brief Ethnographic Sketches

The six tribes are presented below by island and withineach island, by the date of study. For more ethnographic

*This was the Clinical Pathology Laboratory (Dr. F. Neale,Director), Sydney Hospital, Sydney, Australia. In 1966, cholesteroldeterminations on the Nasioi and Kwais tribes were performed byDr. B. Goldrick. We express here our gratitude to these colleagues.

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O nOr 4(.e C -',0OCC 15.)k 2^00 5c' 30(CSA O --_- -__A UAT_:SCALEOF StTAUTE MILEG AT EQUATOR

Figure 1

Map of Solomon Islands region. The location of each of the six tribal groups is indicated.

detail, the reader is referred to the publications of theseveral social anthropologists.23 28

All six tribes are Melanesian. Although importantdifferences in acculturation were present, as detailed below,all were living in tribal villages in rural areas, where motorvehicles, electricity, and other Western conveniences were

totally absent. Homes and buildings were constructed fromlocal materials. Coconut was used in small quantities by allsix groups but was not an important dietary item in any. Useof pipe tobacco was widespread among all age groups andboth sexes in all six. Betel chewing was universal butgenerally moderate in quantity. Use of alcohol was negligi-ble in all groups.

The Nasioi

The Nasioi, studied in 1966, lived in small villages in hills10-15 miles from the coastal town of Kieta, in EasternBougainville. They had had continuous contact with Euro-pean culture for over 80 years. Religion was RomanCatholic, and primary education was universal among theyoung. Economy was predominantly settled agriculture,with cash cultivation of coconuts and cocoa beans. Nasioimen worked intermittently for wages in European ownedenterprises, chiefly plantations. Their dietary staple was

sweet potato (Ipomoea Sp.), supplemented by purchasedtinned meat, fish, rice, and bread. Salt was used regularly incooking. Pigs and chickens were raised, but consumed onlyon festive occasions. Bananas and other fruits were alsoused. Malaria and yaws had been virtually eradicated in the

area. Immunization and maternal and child care wereavailable locally. Medical care in Kieta was accessible to thevillages by footpaths and rough vehicular trails. The studygroup included 256 Nasioi, representing 91% of the definedsample.

The Nagovisi

Studied in 1970, the Nagovisi lived in the inland coastalplain near Empress Augusta Bay, southwestern Bougain-ville. The area was occupied by Japanese forces early inWorld War I1, and the people suffered severe privation dur-ing this period. Contact with Western culture had been con-tinuous since 1931.

Although remote from town, the area was accessible by ajeep road. Two Roman Catholic missions provided educa-tion and medical care. A cooperative store supplied Westerndietary items and other goods. Economy, religion, and dietamong the Nagovisi were similar to those described for theNasioi. Most households consumed some kind of Europeanfood every other day, and many used such foods every day.Four hundred ninety-three persons, representing 96% of thedefined sample, were examined.

The Aita

The Aita, studied in 1970, lived in small villages at anelevation of 3000 to 4000 feet on the slopes of Bougainville'shighest mountain, in the North Central part of the island.Because of their remote location, at considerable distance

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from any road and accessible only at certain times of theyear by steep and rigorous trails, they were little known un-til 1964. Since then there had been an influx of missionariesand government aid programs. Cannibalism had been sup-pressed, and most were nominally Christian, but the impactof religious change on local custom had been slight.Illiteracy was nearly universal. A medical aid station wasstaffed by a native dresser. In 1970, the Aita were swidden(slash and burn) farmers, beginning cash crop cultivation.Aita men had begun to travel out of the area to work as wageearners, mainly in the copper mine, and to sell handicraft.Their staple diet was taro (Xanthosoma sp. and Colocasiasp.) supplemented by sweet potato (Ipomoea sp.) greens,and fruit. The Aita did not raise pigs or chickens. Rice andtinned fish were brought in occasionally in small quantities.Salt was not used in cooking.

Four hundred sixty-seven persons, representing 92% ofthe defined sample, were examined.

The Kwaio

Studied in 1966, the Kwaio lived in scattered hamlets of10-20 persons each in the rugged hilly terrain of East-Central Malaita. Contact with Europeans, begun 25 yearsbefore the study, was slight and intermittent. All subjects inthe sample had retained traditional pagan religious beliefsand practices. Western education and medical care were vir-tually absent in 1966.The Kwaio were swidden farmers, shifting their fields

from year to year. Cloth, metal tools, tobacco, and fish wereobtained through barter with coastal natives. Their diet was85% sweet potato (Ipomoea sp.), supplemented by leafyvegetables with grubs, insects, and fresh water prawns usedas relishes. Pigs were eaten only on ceremonial occasions,mainly by men. Salt was used rarely during ceremonial oc-casions. Twenty-eight men, asked when they had last eatensalt, gave a range from one week to one year, with a medianof 18 weeks. European food was unavailable. Althoughyoung men typically worked on plantations elsewhere in theSolomons for two or more years, (a long-establishedcustom), they reverted completely to traditional ways ontheir return.

During our study, the Kwaio were in the midst of an out-break of severe respiratory disease later diagnosed from ourserum samples as influenza A, Asian type. Because of illness,the 443 Kwaio examined represent only 78% of the residen-tially defined population, the lowest percentage among thesix groups.

The Lau

Studied in 1968, the Lau lived on small artificial islands,one to two acres in area, in a large coastal lagoon inNortheast Malaita. The population density on these islandsaveraged 200 to 250 persons per acre (as great as any knownhuman population), but there was unlimited space in thelagoon and on the mainland accessible by dugout canoe.Missions had been present in the lagoon for 50 years.However, the study subjects were all among the hold-outs," living on islands sacred to pagan gods and retainingtheir traditional beliefs and practices. Education andmedical care were available at the missions but were seldomsought by the pagans. The Lau were fisherman and obtainedvegetables from gardens on the mainland and by trade withthe neighboring Baegu. Some cash was generated by sale ofshells and by jobbing with cooperatively owned boats. Their

Circulation. Voltume XLIX, Jtne 1974

diet was 15% fish, the rest mainly taro, sweet potato, andgreens, all cooked in copious amounts of sea water. Oc-casional pigs, shellfish, and nuts supplied additional protein.Some rice, tinned fish, and meat was purchased from tradingships. Four hundred forty-two persons, representing 95% ofthe defined population, were examined.

The Baegu

Studied in 1968, the Baegu lived near the coast inNortheastern Malaita, just inland from the Lau. Contactwith missions and government representatives had beenpresent intermittently among the Baegu for 25 years. Ap-proximately two-fifths of the study subjects were nominallyChristian, and the rest pagan. Primary education wasavailable to Christian children. Medical care was availableat a mission station approximately 15 miles away by trail andcanoe. The Baegu were predominantly swidden farmers oftaro and sweet potato, beginning to change to settledagriculture and cash-crop cultivation. Fish was obtained bytrade with the Lau. Canned fish and meat were occasionaldietary items. Salt was seldom used in cooking. Four hun-dred eighty-five persons, representing 95% of the definedpopulation, were studied.

Results and Interpretations

Acculturation

Cultural, demographic, and physical data havebeen used as a basis for ranking the six societies inrespect to acculturation. Factors considered includeevidence of demographic change within the definedpopulations, secular increase in adult height, lengthand intensity of contact with Western cultural in-fluences, religious belief, education, availability ofmedical care, economy, and diet.

DemographyThe demographic structures of each of the study

samples, and of the United States are shown in figure2. Demographically "young" societies characteris-tically show an increase in numbers of persons in theearly decades of life, reflecting the effects of increasedbirth rates, reduced infant and child mortality, orboth.'6 This pattern holds in five of the six societies.The Kwaio, the least acculturated, (see below) showedthe least tendency toward this pattern, probablyreflecting a continuing balance between moderate fer-tility and early mortality. The tall, narrow pyramid forthe United States denotes an 'old" society with lowbirth and death rates.

Sectular Trend in Adult HeightAdult height of males and females in each age

group is shown in table 1 for each of the six societiesand a representative sample of the U.S. population. Asecular change toward increasing height in successivegenerations reflects improvement in health, par-ticularly nutrition, during growth.29 Among males, in-

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d 9

NAS10

d _ 9

j

NAGOVS

C Q

AIgTA

Figure 2

LUld 9

KWAO

d 9

Relative demographic structure of six residentially definedpopulations in the Solomon Islands and the United States (not tosame scale). Horizontal bars show numbers of males (left) andfemales (right) for each quintile of age (0-4, 5-9, etc.).

creasing height is observed in the Nasioi, and in theyoungest decade of Nagovisi and Lau, but not in theBaegu, Aita, or Kwaio. Among females, it is present inthe Nasioi, and the youngest Lau and Baegu, but notin the Nagovisi, Aita, or Kwaio. Absence of this trendin the Nagovisi females may reflect their severe priva-tion during and following World War II.

Dietary Change and Salt Intake

Data on diet were obtained from several sources. Ineach society, observations on dietary habits over aperiod of 18 to 24 months were recorded by thecultural anthropologist. Where trade stores were pres-ent, records were kept of the quantity of foodstuffssold over a six-month period, and the number ofhouseholds served. To obtain data on utilization ofsalt, interviews based on recall were conducted. Ran-dom urine samples were collected for determinationof sodium, potassium, and creatinine. Tribal taboosprevented collection of more than a few urine samplesin the less acculturated groups, and timed urinecollections could not be obtained. Based on all dataavailable, our estimates of average daily salt intake forthe six societies are as follows: Nasioi and Nagovisi50-130 mEq; Lau 150-230 plus mEq; Aita and Baegu10-30 mEq; Kwaio, less than 20 mEq (see table 2).

Acculturation Rank

Data on the duration and intensity of contact withWestern influences, change in religion, education,availability of medical care, entry into cash economy,and dietary change have been reduced to ordinalscales. Table 2 summarizes data from all sources bear-ing on acculturation, and assigns rank and degree ofacculturation for each of the six societies. By thesecriteria, the Nasioi, Nagovisi, and Lau display agreater degree of acculturation than the Baegu, Aita,and Kwaio. Data on habitat, subsistence, and salt in-

Table 1

Secular Trend in Adult Height (mm) For Six Solomon Islands Populations and the United States

MalesNasioi Nagovisi Lau Baegu Aita Kwaio U.S.3a

Age (N) (61) (N) (114) (N) (81) (N) (137) (N) (89) (N) (130) (3,019)

18-24 (11) 1639 (17) 1615 (12) 1657 (21) 1399 (20) 1591 (23) 1612 174525-34 (19) 1633 (18) 1593 (14) 1633 (30) 1627 (28) 1599 (25) 1613 175535-44 (22) 1618 (27) 1589 (14) 1617 (33) 1606 (25) 1618 (26) 1616 174045-54 (7) 1602 (29) 1602 (21) 1637 (34) 1609 (13) 1610 (34) 1596 173255-64 * (12) 1590 (14) 1591 (9) 1630 (13) 1608 171265-+ * (11) 1574 (7) 1623 (11) 1592 (8) 1554 16991Increase Yes Youngest Youngest No No No Yes

only onlyFemales

(66) (112) (113) (116) (97) (131) (3,511)

18-24 (15) 1541 (27) 1512 (36) 1538 (13) 1535 (23) 1489 (32) 1486 162125-34 (12) 1515 (21) 1524 (18) 1516 (35) 1495 (35) 1503 (34) 1500 161835-44 (21) 1315 (29) 1493 (20) 1320 (34) 1512 (24) 1518 (26) 1502 161345-54 (9) 1458 (20) 1516 (23) 1516 (16) 1497 (1 1) 1539 (26) 1477 159855-64 (7) 1470 (1 1) 1483 (7) 1508 (10) 1475 * (1 1) 1468 158565-+ * (13) 1458 (8) 1491 * 15621Increase Yes No Youngest Youngest No No Yes

only only

*Fewer than seven persons.tMeans for age group 65-74 years.

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LENGTH SIGN/F/CANTCONTACT (yrs)

INTENSITr of CONVTACT

CHRISTIANITY

MED/CAL CARE

LITERACY/EDIUCATIONV

WESTERN oIET

CASHJ ECONOMY

SECUL-AR TRENDin HEiGH/T

DEMOGRAPHIC CHANGEUN,DER 15/OV/ER45

HABITAT

SUBSISTENCE

SALT IvTAKE(mEI/nE 24hrs)

ACCUlLTrURATrION ORDER

ACCUZLTURATION DEGREE

TABLE 2: INDICES OF ACCULTURATION -6 SOCIETIES

NASIOI NAGOVISI LAU BAEGU AITA KWAIO

85 30 50 25 6 25

++++++ ++ + ++ +

___ _ 0+++ O + ++ 0

++ + + + + + 0+++ ~ ~ ~~~++ 0 0

+++ +4-++ -4++ + + 0

+++ +++ + + + + 0

YES YOUNGEST YOUNGEST YOUNGESTMALES ONLY ONLY FEMALES ONLY NO NO

4.4 2.9 2.6 2.4 7.9 1.7

COASTAL HILLS INLAND PLAIN SMALL ISLANDSNEAR TOWN NO TOWN COASTAL LAGOON INLAND HILLS MOUNTAINS INLAND HILLS

AGRICULTURE AGRICULTURE FISHING SWIDEN/AGRIC. SWIDDEN SWIDDEN

50-130 50-130 150-230 10-30 10-30 <20

1 2 3 4 5 6

+++ +++ ++ + + 0

Ordinal scales based on data summarized in ethnographic sketches

take are included in table 2 for comparison but were

not used in ranking acculturation.

Physical Characteristics and Health

Tables 3 and 4 summarize physical measurementsin all six societies in comparison with a U.S. popula-tion sample.30 The Lau were heavier on the average

than the other societies though below means for theU.S. sample in measurements reflecting body fat.Despite low protein intake, physical signs of malnutri-tion and protein starvation were virtually absent bothin children and adults. A high prevalence of malaria inthe Baegu and Kwaio is indicated by the high rates ofenlarged spleens in children aged 2-9 years in these

Table 3

Physical Characteristics in Six Societies-Males Aged 20 and Over

Tribe Nasioi Nagovisi Lau B3aegu Aita KwaioIsland Bougainv. Bougainv. Malaita Malaita Bougainv. Malaita U.S.A.

Number 59 109 77 126 81 127 3,091 30 *Height (in) 63.8 62.8 64.0 63.5 63.2 63.1 68.2Weight (1b) _ _127 126 142 126 132 123 168Ponderal Index, ht. \t wt. 12.72 12.56 12.31 12.68 12.42 12.72 12.40Arm circumference (mm) 267 276 295 264 272 260 307Skinfold-triceps (mm) 5.4 5.9 6.2 5.2 5.6 5.4 13.0

subscap. (mm) 8.3 9.9 9.3 8.3 10.5 8.8 13.0Chest brdth. (mm) 258 255 276 258 262 259 300Chest depth (mm) 214 214 222 212 218 214 226Chest depth/brdth% 83.0 84.0 80.3 82.2 83.0 82.5 75.3Hemoglobin (gm/100 ml) 14.4 13.8 14.3 13.1 16.1 14.0 15.5Enlarged spleen (percent of both 7.5 4.1 6.0 92.0 5.2 52.2

sexes, ages 2-9)Parasites, stool (percent of stools 85.0 87.0 94.0 25.0 97.0

examined, all ages)No. of parasites/pos. stool (all ages) i.8 1.6 2.6 1.3 2.6

*Includes 18 - and 19-year - olds.

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Table 4

Physical Characteristics in Six Societies-Females Aged 20 and Over

Tribe Nasioi Nagovisi Lau Baegu Aita KwaioIsland Bougainv. Bougainv. Malaita Malaita Bougainv. Malaita U.S.A.

Number 63 101 101 111 88 114 3,58130*Height (in) 59.2 59.2 59.8 59.2 59.3 58.7 63.0Weight (1b) 103 105 120 104 116 102 142Ponderal Index, ht. x/' wt. 12.64 12.60 12.17 12.60 12.21 12.61 12.15Arm circumference (mm) 233 242 263 228 260 228 284Skinfold-triceps (mm) 7.9 10.1 10.9 8.4 10.5 7.9 22.0

subscrap. (mm) 9.8 12.6 12.7 10.2 13.2 11.8 18.0Chest brdth. (mm) 235 231 256 237 245 238Chest depth (mm) 194 195 198 195 205 199Chest depth/brdth% 82.6 84.2 77.4 82. 83.8 83.5Hemoglobin (gm/100 ml) 13.3 11.6 12.6 11.6 13.5 12.7 13.7Enlarged spleen, percent of both 7.5 4.1 6.0 92.0 15.2 152.2

sexes, ages 2-9 yrsParasites, stool (percent of female 83.0 86.0 89.0

stools examined, all ages)No. of parasites/pos. stool (all ages) 1.6 2.2 2.5o

*Includes 18 - and 19-year - olds.

populations. Nevertheless, hemoglobin levels are nor-mal in males, and in females only slightly low in theBaegu, whose mean value of 11.6 gm/100 ml equaledthat of the Nagovisi females who have a lowprevalence of splenomegaly. Abundant intestinalparasites were present in all groups whose stoolsamples were obtained. Physical fitness in all groupsappeared excellent, judged by the ability of bothmales and females to carry heavy loads for many milesuphill.

Serum Cholesterol and Uric Acid

Figure 3 shows means for serum cholesterol levelsin relation to age for males and females in each of thesix societies and a U.S. sample.3' The methods forcholesterol determination used in both studies givecomparable results.32 In contrast to the U. S. rise withage, there was no clear age trend in cholesterol in theSolomon Islands societies. At almost all ages and bothsexes, the three more acculturated populations hadhigher values than the three less acculturated ones.

It is noteworthy that among the less acculturatedpopulations, serum cholesterol was highest among theyounger members of the Aita tribe, who had had themost recent exposure to Western cultural influencesand who were undergoing the most rapid rate ofchange.

Differences in the use of coconut have been cor-related with serum cholesterol levels in Polynesianisland dwellers.33 However, although all six Solomonspopulations used coconut, there were no largedifferences in the extent of use among the six, and itwas not an important dietary staple in any. It is possi-

ble that the introduction of animal fat in tinned meatand fish may partially or wholly explain thedifferences in cholesterol levels since in the absence ofthese items the traditional diet of root crops is ex-tremely low in fat.Mean values for serum cholesterol and uric acid

appear in table 5. In relation to acculturation,reciprocal results are seen in the two determinations.The three more acculturated societies show highercholesterol and lower uric acid levels, while the threeless acculturated societies show lower cholesterol and

x USA MALES FEMALESo Nasioi

280- o Nagovisi6. LouX* Boegu

240 Kwoio

200-

1 20-

80

15-19 20-29 30-3940-4950-59 60-69 70+ 15-1g 92 930-39 40-4950-59 60-69 70+

AGE (years)Figure 3

Serum cholesterol levels by age for males and females in sixSolomon Islands societies. Values for a U.S. population samples' areincluded for comparison.

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Table 5

Means and Standard Deviations for Cholesterol andUric Acid in Six Societies

Number Cholesterol Uric acid

Nasioi Male 59 155 - 33.5 5.97 $0.88Female 63 165 - 32.9 5.16 i0.86

Nagovisi Male 109 161 - 35.1 5.27 i0.88Female 101 162 - 35.2 4.56 0.90

Lau Male 77 149 - 27.0 5.47 i 0.93Female 101 160 30.7 4.83 i1.0

Baegu Male 126 115 26.9 6.16 1.56Female 111 119 28.5 5.81 1.39

Aita Male 81 135 i 29.1 6.11 1.10Female 88 142 30.2 5.89 -1.05

Kwaio Male 127 114 28.7 6.47 1.60Female 114 125 31.6 5.70 1.40

higher uric acid levels. The uric acid levels of allSolomon Islands groups, except the Kwaio, were lowerthan those of white Australian males (6.28 ± 1.23mg/100 ml) determined in the same laboratory.3'

Several investigators have reported high serum uricacid levels among Pacific peoples, especiallyPolynesians.35' 36, 37 However, where differences in ac-culturation are present, uric acid has usually beenfound increasing together with cholesterol in the ac-culturated societies.36' 38, 39 An exception is the studyof Jeremy and Rhodes,`0 who found the serum uricacid levels higher in primitive New Guinea villagersthan in people of similar origin who had been towndwellers for 12 years or more. Their observations thusparallel our own, suggesting that a reduction in uricacid level occurs at an early stage of acculturation.

The use of alcohol was negligible in all six groupsand may therefore be excluded from consideration.Jeremy and Rhodes40 attribute the high serum uricacid of New Guinea villagers living on sweet potato totheir habitually low sodium intake. When salt wasadded to the sweet potato, uric acid levels of their sub-jects fell. Although the mechanism of this effect isobscure, it could provide an explanation for thedifferences noted among the Solomon islanders,whose basic diet was similar to that of the New Guineavillagers. Presumably, a secondary rise in serum uricacid would be anticipated at a later stage of accultura-tion, as diets richer in animal fat, protein, and possiblyalcohol are adopted, and indeed, such seems to be thecase in New Guinea.40

Blood Pressure

Mean blood pressure is shown in relation to age forall six societies for males in figure 4 and for females infigure 5. For both males and females, the Lau hadhighest systolic and diastolic pressures at almost allages.The statistically significant coefficients of correla-

tion of blood pressure on age are shown in table 6. Anincrease in systolic pressure with age was present infemales in the three more acculturated societies. Nosignificant age trend in systolic pressure was present inmales. However, diastolic pressure fell with ageamong males in the three less acculturated societies.Diastolic pressure also declined with age in Nagovisimales.Weight was negatively correlated with age in all

groups studied (table 6), a relationship that was strong

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Circulatiol, Volulme xIX, Juine 1974

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Table 6

Coefficients of Correlation for Age, Body Weight and Blood Pressure*

Nasioi Nagovisi Lau Baegu Aita Kwaio

MalesNumber 59 109 77 126 81 127Age & weight -0.18 -0.29* -0.36* -0.40*Age & systolic blood pressure -0.18Age & diastolic blood pressure -0.19 -0.24* -0.29* -0.20Weight & height 0.67* 0.60* 0.58* 0.61* 0.63* 0.58*Weight & systolic blood pressure 0.24*Weight & diastolic blood pressure 0.22 0.27*

FemalesNumber 63 101 101 111 88 114Age & weight -0.40* -0.26* -0.38* -0.49* -0.48* -0.45*Age & systolic blood pressure 0.36* 0.30* 0.36*Age & diastolic blood pressure -0.16Weight & height 0.64* 0.61* 0.55* 0.50* 0.46* 0.58*Weight & systolic blood pressureWeight & diastolic blood pressure 0.26* 0.30*

*Only those coefficients of correlation which couldincluded in the table. An asterisk denotes P < 0.01.

among females. In view of this, the positive correla-tion of systolic blood pressure with age among themore acculturated females cannot be attributed toweight gain. This observation is reinforced by the in-dependence of weight and systolic pressure in thesegroups. A similar discrepancy of weight and bloodpressure with age is rarely found in advancedsocieties. Among the males both weight and diastolicblood pressure decline with age in all six groups. Themost definite age-related decline in diastolic pressurewas found in the three less acculturated groups.

Table 7 shows the percentages of subjects in eachgroup with blood pressure in excess of 140 systolic and90 diastolic. The figures of 7.8% and 9.9% for the maleand female Lau are substantially greater than for anyof the other societies.

Studies reported from many different parts of theworld have documented the absence of a rise in bloodpressure with age among primitive populations living

Table 7

Subjects Age 20 and Over with Blood Pressure Exceed-ing 140 Systolic and 90 Diastolic

Males FemalesTribe N N > 140/90 % N N > 140/90 %

Nasioi 59 2 3.4 63 0 0Nagovisi 109 3 2.7 101 0 0Lau 77 6 7.8 101 10 9.9Baegu 126 1 0.8 109 0 0Aita 81 0 0 88 0 0Kwaio 128 1 0.8 114 1 0.9

be shown statistically not to be zero (P < 0.05) are

in isolation. 9̀ In some of these populations a signifi-cant decline of both systolic and diastolic pressure hasbeen found in the older age groups.', 5 In previouslyreported studies, detailed cultural and demographicdata have often been lacking, and the ages and stateof health of the subjects have been uncertain. It hasbeen suggested that the failure of blood pressure torise with age may be due to chronic disease andmalnutrition,4` the normal rise emerging as health andnutrition improve.The Baegu, Aita, and Kwaio populations of the

Solomon Islands represent further examples of "lowblood pressure" populations. However in these groupsnutrition, physique, and physical fitness appeared tobe good. Malaria was prevalent in the Baegu and to asmaller extent in the Kwaio, but was uncommon inthe Aita. Hemoglobin values in all three groupsresembled those of the three more acculturated pop-ulations. These findings contradict the hypothesis thatlow blood pressure in Solomon Islanders is due to poorhealth.

Electrocardiographic FindingsThe most striking finding among the electro-

cardiograms from these six Solomon Islands popula-tion groups was the lack of significant abnormality,particularly in those items usually associated with cor-onary heart disease. Table 8 lists the number andprevalence of codable items found among the com-bined adults in all six population groups. Tables whichinclude the findings for each of the six groupsanalyzed separately have been deposited with TheNational Auxiliary Publications Service and may be

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CARDIOVASCULAR DISEASE IN TRIBAL SOCIETIES 1141

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Table 9

Prevalence of Certain ECG Findings in Total Population Groups-Comparison of Solomon Islanderswith Two North American Populations

Tecumseh, Tecumseh,Blackburn Solomon Michigan Michigan H"H'Code Item Sex Islands 1959-609 1962-6549 groupm

I Male 0.5 2.2 2.5 2.5(Q waves) Female 0.6 1.0 1.5 1.6

II-1 Male 2.3 6.0 5.0 2.1(left axis deviation) Female 0.3 3.8 2.8 1.3

III-1 Male 13.9 6.0 3.0 19.9(High amplitude R waves) Female 1.4 2.3 1.1 11.9

IV Male 0.3 2.5 2.1 4.8(ST segment abnormalities) Female 0.5 5.4 3.8 13.7

V Male 2.7 11.6 8.2 8.9(T wave abnormalities) Female 11.3 13.1 7.3 10.3

VI-3 iMale 1.6 1.9 1.a 3.8(Prolonged P-R interval) Female 0.3 1.8 0.9 2.3VII-1 Male 0.2 0.2 0.3 0.2

(Left bundle branch block) Female 0.2 0.4 0.4 0 .5VIII-1 Male 1.3 2.5 0.9 0.7

(Frequent premature beats) Female 0.2 1.9 0.9 0.6VIII-3 Male 0 0.3 0.5 0.1

(atrial fibrillation or flutter) Female 0 0.5 0 .5 0.1

obtained upon request. * The over-all prevalence ofcodable items was strikingly low, with the exception ofhigh voltage R-waves (item 111-1), among males andof T-wave abnormalities (item V) among females.

Table 9 provides a comparison of the prevalence ofECG findings among the entire study population ofSolomon Islanders with similar prevalence data fromrecently reported studies of North American pop-ulations. The H group, who are religious isolates, areincluded for comparison since this Caucasian popula-tion shows a high prevalence of R waves similar to theSolomons sample. An alternate method of comparisonis presented in table 10 which lists the prevalence ofcertain ECG findings commonly associated with cor-onary heart disease among 40-59-year-old males in theSolomon Islands group and in various other pop-ulations throughout the world.42 The Gau43 andTukisenta44 populations represent the only two otherMelanesian groups from which ECG findings areavailable. It is of interest to note that the prevalenceof abnormalities among these populations is also low,albeit not as low as among the Solomon Islanders.Only one of the 1267 tracings from the Solomons sam-ple contained large Q waves (item-I-1), which are

*See NAPS document 02360 for 6 pages of supplementarvmaterial. Order from ASIS/NAPS, c/o Microfiche Publications, 305E. 46th Street, New York, New York 10017. Remit in advance foreach NAPS accession number, $1.50 for microfiche or $5.00 forphotocopies up to 30 pages, 15 cents for each additional page. Makechecks pavable to Microfiche Publications.

strongly suggestive of myocardial infarction. This wasobtained from an Aita female in the 60-69-year-agegroup. Over-all prevalence of Q items was very low inthe entire population. In fact, we were unable to findany comparable populations with a lower prevalenceof Q wave items as determined by the criteria ofBlackburn et al., although the studies reported fromUshibuka, Japan,42 demonstrated a prevalence among40-59 year old males which was almost as low (table10). The prevalence of left axis deviation (item 11-1)was also low, but much more striking was the lack ofST segment depression (item IV). Only 0.3% of malesand 0.5% of females demonstrated these findings, ascompared with rates of 2.1-13.7% in recent Americanstudies (table 9). T-wave abnormalities (item V) wererare among Solomon Islands males, but not amongfemales. In both groups, almost all codable T-waveitems occurred because of T inversion in the rightprecordial leads (table 11), a finding which is notusually associated with coronary heart disease. Anumber of studies have suggested that inverted45 ordiphasic4" right precordial T-waves are prevalentamong American Negroes, in whom it has been felt torepresent persistence of the "juvenile" T-wavepattern. Other studies, however, have not confirmedthis finding.47Higher prevalences of inverted T-waves in the right

precordial leads of females than males have also beendescribed among Africans and Indians in Guyana4and among certain Negro populations.48 The etiologyof the inverted right precordial T-waves among

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Table 10

Prevalence of Certain ECG Findings in 40-59-Year-OldOther Populations

Males-Comparison of Solomon Islanders with Several

Rate (%)Tukisenta, Tecumseh,

Solomon Gau, Fiji New Michigan "H' Crevalcore, Karelia, Crete, Tanushimaru, Ushibuka,Blackburn Islands Islands43 Guinea44 1962-196549 Group53 Italy42 Finland42 Greece42 Japan42 Japan42Code Item N = 243 N = 117 N = 139 N = 869 N = 320 N = 993 N = 814 N = 683 N = 504 N = 484

(Q waves) 0.4 2.6 0.7 2.9 3.1 3.5 2.2 1.3 2.2 0.6II-1

(left axis deviation) 1.6 1.7 2.9 5.8 3.5 4.1 2.9 4.7 0.8 0.6Iv

(ST segmentabnormalities) 0.4 4.3 0.7 2.1 4.7 4.0 3.3 2.0 13.5 9.9V

(T waveabnormalities) 1.2 4.3 5.8 9.1 11.9 5.5 8.6 2.5 3.9 2.7

Solomon Islands females is not clear, but its majorsignificance lies in the fact that this change con-tributes most heavily to the number of codable T-wave items observed in the females. Of 90 codable T-wave items found in the entire population, only-threeinvolved leads V5 and V6. Thus, it is unlikely that theprevalence of T-wave items in these subjects is relatedto coronary heart disease or left ventricular hyper-trophy.High voltage R waves in the left precordial leads

were found most frequently in the Nasioi males (rate51.6%) and to a lesser extent among Kwaio (17.3%)and Nagovisi (16.5%) males. The rates for the Aita,Baegu, and Lau males (3.0%, 6.8%, and 3.3%, respec-tively) were comparable to those found in the popula-tion of Tecumseh, Michigan.49The reason for the high prevalence of tall R-waves

in the Nasioi is not clear, but the fact that the femalesas well as the males have R waves which are tallerthan those in the other Solomon Islands populationsstudies suggests that it may be a genetic trait. Therewas a significant positive correlation of R wave voltage(RV5) with both systolic and diastolic pressure(r = 0.40; P < 0.001) in this group although only

3.5% of Nasioi males showed blood pressures in excessof 140 systolic and 90 diastolic. Similar correlations ofR wave voltage with age have been noted in otherpopulations.50' However, the lack of significantsystolic or diastolic hypertension in the Nasioi makesit most unlikely that the tall R waves noted here are anexpression of hypertensive hypertrophy as has beensuggested to be the case among certain Caucasianpopulation groups.52A high prevalence of high amplitude R-waves was

found among young males of the H group in WesternNorth America by Goldbarg et al.53 (40.5% in 16-19-year-old males). This prevalence decreased rathermarkedly with age and was thought to be associatedwith the heavy physical work performed by these per-sons. The R wave voltage also decreased with age inthe Nasioi males. Although we have no concretemeasure of physical activity in the Solomon Islandsgroups, it is unlikely that physical activity can accountfor the high prevalence of increased R wave voltageamong the young Nasioi males since most of theheavier physical labor was performed by the women,an activity pattern which was also present in the otherfive groups. Therefore, we are left with the possibility

Table l 1

Location of Inverted T-Waves-Precordial Leads

Males Females0 V1 VI 2 V1_3 Vl14 V4-6 0 Vi VI 2 V1_3 V1l4 Vs V-6

Na.sioi 39 23 2 0 0 0 17 42 9 2 0 0 0Nagovisi 35 32 2 0 1 1 32 67 16 6 0 1 0Lau 49 41 0 0 0 0 27 77 15 6 1 0 1Baegu 94 46 3 2 1 1 33 67 14 9 3 0 0Aita 71 22 3 3 0 0 46 42 9 9 2 0 0Kwaio 63 35 0 0 0 0 29 49 16 0 0 0 0Total 401 199 10 5 2 2 184 344 79 32 6 1 1

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that the high R wave voltage in the left chest leads ofthe Nasioi also represents a genetic trait.

Discussion

In analyzing the data obtained from the sixSolomon Islands societies, many different correlationswere tested in an attempt to relate physical andcultural differences to the observed changes incholesterol, uric acid, and intrapopulation trends inblood pressure in relation to age.

When independently developed indices of ac-

culturation were used to compare the differentsocieties (table 2), a number of clear differencesemerged between the more and the less acculturatedgroups.

Our data suggest that the failure of blood pressure

to rise with age may be biologically normal, and thatwith acculturation, a constellation of changes is en-

trained, which include an increase in serum

cholesterol, a reduction in serum uric acid, and an

age-related rise in blood pressure, which expresses

itself earliest, and most noticeably in the females.Data from several parts of the world suggest that theblood pressure change is a general phenomenon, notconfined to the Solomon Islanders. AmongMelanesians in New Guinea, Maddocks' found thatthree primitive groups of villagers showed decliningblood pressure with age. By contrast, in the towndwellers near Port Moresby, blood pressure rose withage, and the steepest increase was in the systolicpressure of females. Prior and Grimley-Evans3 foundblood pressure rising steeply with age in both malesand females in the acculturated town dwellers ofRoratonga, whereas in less acculturated Pukapuka,the only trend noted was some increase in systolicpressure in females. Abbie and Schroder reportedsimilar trends among Australian aborigines.9 Glanvilleand Geerdink54 examined Amerindians of Surinamafter six years of "jarring contact with outside in-fluences." They found systolic pressure rising with age

among women, while it remained level in men.

Further evidence that acculturation may initiatethe age-related rise in blood pressure may be adducedfrom surveys conducted among the Kisii of Ugandaover a period of 40 years. Donnison55 studied a sampleof 893 of these people, and reported in 1929 thatblood pressure fell with age. A similar, but not iden-tical sample studied by Williams in the late 1930sshowed blood pressure neither rising nor falling withage.56 People of the same area, by now fairly ac-

culturated, were recently studied by Shaper, whoreported, in 1969, that blood pressure rose with age as

steeply as in any Western society.57If, as suggested here, the process of acculturation is

associated with biologic changes which lead to thedevelopment of risk factors for cardiovascular disease,it is obviously important to identify the factors com-mon to those societies in which these changes occurand absent from those in which they do not. For theSolomon Islands populations, which were all at fairlylow levels of acculturation, several factors, commonlypresent in changing societies, can be excluded. All sixsocieties lacked motor vehicles and developed roads.Thus patterns of locomotion and physical activityremained unchanged. Similarly telephones, elec-tricity, industrial and household equipment, noise,pollution, and smog were all absent. Some changes intribal custom had occurred where Christianity hadreplaced pagan belief, but social and family roles hadremained essentially unchanged. Entry into the casheconomy and wage earning employment may have in-troduced stresses which are difficult to assess, butthese activities were confined to males, who showedless change, at least in blood pressure, than females.Crowded living conditions were present among the

Lau, who lived on small artificial islands. However,even on these islands, space was partitioned intosegments, with a sacred area restricted to men, and anarea for women to occupy during menses, in additionto the densely crowded area for family life. Both menand women left the islands during the day to engagein activities such as gardening and fishing in the sur-rounding uncrowded lagoon and mainland. Crowdingamong the Lau is the traditional mode of life58 and isvoluntary. A similar pattern of voluntary crowding hasbeen reported in the ! Kung of Botswana," whereblood pressure remains low throughout life.The most constant change among the more ac-

culturated Solomon Islands populations, not sharedby the less acculturated, was the adoption of Westerndietary items, especially salt, tinned meat and fish andrice. Data presented in tables 3 and 4 do not suggestthat this change had had any consistent effect on bodyweight or other indices of body fat such as ponderalindex and skinfold measurements. Heaviest were theLau (third in rank of acculturation) and next to themthe Aita (fifth in rank). Further, as shown in table 6, inall three societies which show rising pressure with age,weight decreases with age.

Suspicion thus falls most heavily on salt intake,which was substantially greater in all of the more ac-culturated groups. Of particular interest in this con-nection are the Lau, who because of the custom ofcooking vegetables in sea water had by far the highestsalt intake of any group. The Lau exhibited thehighest systolic and diastolic blood pressures in bothsexes and nearly all age groups of the six societies. Ourfindings are thus consistent with the hypothesis of

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Dahl60 that the level of blood pressure in populationsmay be correlated with sodium intake. Shaper41 hasalso noted that "low pressure" populations are "lowsalt" populations.

Public health reports indicate that clinical coronaryheart disease and atherosclerosis are very rare in theSolomon Islands. Although not an index of systemicatherosclerosis, retinal examinations conducted by thesame ophthalmologist (D. L. Verlee) in all sixSolomons societies showed a striking absence ofretinal arteriosclerotic changes even in the elderly. Apreliminary report of these findings has beenpublished.6"The over-all low prevalence of codable ECG items

is consistent with an almost total lack of coronaryheart disease in these subjects. Thus, even among themore acculturated groups which are beginning to ex-hibit biologic changes which may lead to the develop-ment of risk factors for cardiovascular disease, thesechanges have not been translated into evidence of cor-onary heart disease. The observed differences amongthese groups may represent the earliest antecedents ofcardiovascular disease in emerging peoples. It will beof considerable interest to report studies as furthercultural changes evolve in these societies.

Acknowledgment

The authors wish to thank Mrs. Nancy K. Lubin for statisticaldata analysis.

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