Annals of Tropical Medicine & Parasitology

ISSN: 0003-4983 (Print) 1364-8594 (Online) Journal homepage: https://www.tandfonline.com/loi/ypgh19

A review of cardiovascular diseases in developing countries J.P. Vaughan To cite this article: J.P. Vaughan (1978) A review of cardiovascular diseases in developing countries, Annals of Tropical Medicine & Parasitology, 72:2, 101-109, DOI: 10.1080/00034983.1978.11719289 To link to this article: https://doi.org/10.1080/00034983.1978.11719289

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Anna ls of Trop ical ~lcdicinc and Pa rasi tology, Vol. 72, No.2 (1978)

A review of cardiovascul ar diseases In developing countries Bv J.P . VAUGHAN L ondon School qf Hygiene and Tropical J\1edicine, Gower Street, L ondon WCJE 7HT H.eceived 27 Janumy 1977

The purpose of thi s rev iew is to exa mine th e poss ible assoc ia ti on in und eve lo ped and developing co mmuniti es be tween ' d evelopmen t' and blood pressure, coro na ry hea rt disease a nd rh eum a ti c heart disease. ' D evelopm ent' is used in a broad a nd non-spec ific manner to cover th e whole process whereby soc ie ti es become economi call y more adva nced a nd liv ing sta nd ards ri se, a nd no attempt is mad e to define it more prec ise ly. R a ised blood press ure, hype rte nsion and co ron a ry hea rt di sease (CHD ) have become major prob lem s in th e d eve loped countr ies in rece nt yea rs, yet th ese co nditi o ns are sa id to be infreq uent or absent in so me of' th e more isola ted und evel o ped and developing ' nonwes terni zed' soc ie ti es (Mia ll a nd Bras, 1972; Shaper, 1972; Burket t, 1973 ). It ap pears to be w idel y acce pt ed that m ea n blood pressure rises in old er age gro ups (Boc et al., 195 7; Vita l a nd H ea lth Statistics, 1975), that th e ri sk of' de veloping co m pi ica ti o ns rises with hig her blood press ure levels (K a nnel ] et al., 1969; Evans a nd Rose, 197 1), a nd th a t treat ment with hypo tensive drugs can d ec rease th a t ri sk (V etera ns Administration Coop era ti ve Studies, 1967, 1970; Pi ckering, 1972). The outcome of th e P icker ing ( 1965 ) a nd Platt ( 1963 ) controversy, on whether hype •·tension represcn ted the upper range of blood pressure distributions or a di stinc t geneti c entity, h as now resulted in th e genera l bcli efth a t e nvironm enta l fac tors play th e m ajor part in d e termining b lood pressure level s. Mia ll ( 197 1) summ a ri zed th e ev id ence and sugges ted that geneti c influ en ces contribut e not mo re tha n a third to th e varia nce in b lood pressure levels. If the remaining two- th ird s is environm ent a l in origin, th en a n und e rstanding of th ese environment fac tors cou ld lead to a better prediction of what wi ll ha ppen in d eveloping co untri es a nd what arc th e appropriate preventi ve measures. In some soc ie ti es b lood press ures do not a ppa rently rise with inCJ·casin g age (K ea n and H amm ill , 1943; Lowenstein, 196 1; Lovell , 1967; Hui zinga, 197 1), a nd thi s raises th e question of what a re ' norm a l' blood pressure levels a nd if such developing soc ieti es ca n expect raised blood pressure to become a major problem as 'wes tern iza ti o n ', with d eve lopment a nd accu lturat ion , proceed? The epidemi c o fCHD is quite recent in orig in and in th e United Kingdo m it is now th e lead ing cause of death. The age and sex spec ific mortality rates for CHD show a more or less logarithmi c rise throughout life (Rose, 1972) a nd a g rea t d ea l is now kn ow n a bo ut th e r isk factors or 'markers' by which individuals at g rea ter ri sk can be id entified (Epstein, 197 1 ; British Medical Journal, 1973; S ta mler, 1973 ). There is a lso some good ev id e nce that CHD can be prevented (Stamler, 1973). In deve loping soc ieti es CHD is rare but may be gett ing more frequ ent (Miall a nd Bras, 1972). As these soc ieti es become more d evelo ped, it is re levant to ask if th ey a lso wi ll experience a rise in th e in cid ence of CHD? The incid ence of ac ute rheum a ti c fever and rheumatic hea rt di sease h as fa ll en dramatically in 'wes tern' countries over th e las t 30-40 years and acu te cases are n ow rarely seen (Besterman, 1970; Sievers a nd Hall , 1971 ). Until quit e recent ly, rh eum a ti c hea rt 0003- 4983/78/0401.0 I0 I SO l.00/0

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CARDTOVASCULAR D ISEASES I

DEVELOPING COUNTRIES

disease was said to be un common in th e tropi cs but it is now recogni zed as one of the commones t form s of heart disease in develop ing countries (WHO , 1970 ). Ind eed there is evide nce from those co unt r ies th a t iris freq uently more severe and presents a t a younger age. vVill deve lopment produce a fall in incid ence of rh eum atic hear t d isease in developing countries? The reader may a lso be referred to such recent rev iews on cardiovascul a r d iseases in th e tropi cs as Heart Disease in the Tropics, by Miall and Brass ( 1972 ), Cardio vascular Disease in the TrojJics by Shaper ( 1972 ) a nd a book of th e sa me titl e ed ited by Shaper, l-lutt and Fejfar (1974).

E PID EM IOLOG ICAL METHODS I N CARDIOVASCULAR STUDI ES F rom an ep id emiological view point th ere are two m a in a pproaches to th e questi on of poss ibl e chang ing patterns of raised blood pressure levels, coronary heart disease and rheum atic heart d isease. F irstly one can examine da ta from groups of pcopl who have contrasting freq uenci es of th e di sease, living eith er in th e sa me or different countri es and who a rc not necessa rily from th e sa me or simil ar geneti c stock. Thi s approach has encouraged surveys of ' primitive', 'non-wes ternized' a nd ' un accultu rated' commun iti es in und eveloped and developing societies, w ith a view to compar ing their frequen cy and causes of card iovascul ar di sorders wit h tha t wh ich occurs in 'wes terni zed ' and 'c ivi li zed' developed communities. Secul a r changes can th en be gathered from long term dat a, but thi s approach suffers from th e fact th at genetical ly, and perhaps also environmen ta ll y, th e two groups of people may be very different. Some control of the environm enta l factors can be obta in ed by studying two different racial groups living in th e sa me area. This technique see ms good but is probably more suita bl e for d iseases caused by environme nta l agents th an th ose more related to persona l lifes tyle, as is thoug ht to be th e case with blood p•·essurc and C HD . An alterna ti ve is to look at the same or a simi lar genet ic group th at has comm uni ties or individuals w ho live und er different degrees of development a nd therefore have differe nt environmenta l cond itions (Cassel, 1975 ). In th is way it is hoped th a t the genetic component wi ll rema in static w hil e the effects of different environm ents can be exam in ed. One of the major d iffi cu lties is to esta bli sh how geneticall y simil ar or diss imilar arc th e co mmuni tie or ind ividuals studi ed. Such inves tigati ons a re usually one of two m ain types. The first examines at one particu lar time, or a t differen t times, one geneti c gro up in w hi ch communities live at vary ing levels of d evelopment. Comparison o f two groups at one point in time is based on prevalence data, w hereas exam ina tion of the same commun ity at two differe nt stages in its developm ent ca n be based on longitudinal observat ions. Th ere may be a large number of differences between th e commu niti es a nd to find w hich variables arc significant can pose major prob lems. The main methodolog ical difficulti es are those of the comparab ility of measurements between different surveys. Th e second ma in approach involves th e examination of mig rant individua ls, who move between commun ities, rather than to study th e whole comm uniti es. Here a lso the exa minations can take place at the same time or a fter a period of tim e. The main difficu lty is in th e interpretat ion of any differences a nd in knowing w het her th e migrants are intrinsicall y different in any impor tan t respects from th e or ig ina l popu lation that they left. These various epidem iological approaches have been well rev iewed for blood pressure studies by Cassel ( 1974, 1975 ), who a rgues that the bes t advances in our un derstanding of the aetiology of hypertension may be based on carefully carried out studies in migrant groups. Most of the reported studies have been based on prevalence data and few longitudina l studies have been carried out in developing countries.

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STUDIES I N ' PRIMITIVE GROUPS ' Many blood pressure studi es have been mad e in und eve loped , more ' primiti ve', more ' isola ted' , ' non-wes terni zed ' a nd ' unaccultura ted' popul a ti ons (summ a ri zed by K ca n a nd H a mmill , 1943; Bays a nd Scrim sh a w, 1953; Lowenstein , 196 1; Hui zinga, 197 1; Sh a p er, 1974). Some o ft he more recent surveys have includ ed suc h di ve rse popul a ti ons as Au stra li a n a borigin es (Casley-S mith , 1959; D ongen et al. , 1962 ), P olynes ia ns in th e Pac ific a nd N ew Zeala nd (L ovell , 1967; Prior, 1974), New Guin ea hi ghl a nd a nd low la nd popu la tions (Sinne tt a nd Wh yte, 1973; Stanh?pe, 1973), Mel an esia ns in th e New H e bri des (Norma nT aylor and R ees, 1963 ) a nd Bnttsh Solomons (P age et al. , 1974), Co ngo Ituri Fores t Pyg mies (M a nn et al., 1962 ), n_o mads from north ern K enya (Sh a pcr, Wright a nd K yo bc, 1969), the M asaii from T a nza m a (M a nn et al ., 1964), Braz ili a n Tnd ia ns (Lowenstein , 196 1) a nd Hi ghl a nd Gu a tamal a n Indi a ns ( Hoobl er et al., 1965 ) . Most o f these studi es were ca rri ed out o n p eo pl e who a rc not , if a t a ll , closely rel a ted to th e a ncestors o f th e major p opul a ti on groups. Th eir usefuln ess for co mp a ri sons is th erefore limited. Even a m ong such a vari ety of indi genous p op ul a ti ons a ll th e res ult s support th e conclusion th at m ea n bl ood pressure levels show little or no ri se in old e r age g roups, th a t hy pertension is ra re, th a t C HD ri sk factors a re no t a pparent a nd th a t CHD it self is ex trem el y rare. So m an y different studi es amongs t ma ny different ge ne ti c groups have had similar findin gs that it is unlikely th at th ere is any ge ne ti c or rac ia l immunity to hi g h blood pressure a nd CHD. STUDIES BASED ON ONE GENETICALLY SIMILAR GROUP first, we m ay consid er so me examples of studi es carri ed out a t th e sa me ti me but in differe nt co mmuniti es. Studi es on Pol ynes ian islanders (Prior, 1974), M ela nes ians (M addocks, 1967 ) a nd South African Zulus (Scotch, 1963 ) a ll sugges ted th a t hi gher bl ood pressure levels ex ist a mon g th e more developed and urba ni zed communiti es compa red to rura l popu la tions. A stud y ca rri ed ou t on a gene ti call y hom ogeneous popu la ti on living in two entirely diffe rent e nv ironme nts in highl a nd a nd lowla nd a reas of C hil e (Cruz-Coke et al ., 1973), revea led no hyper tension in th e highla nd p eople. The genet ic co mponent of th e b lood pressure var ia nce was grea ter than th e e nvironm ent a l one in th e accultura ted group li vi ng in th e more d eveloped lowla nd areas . A careful socio-cultural stud y was carri ed out a mongst Papago Indi a ns in th e U nit ed States (Patrick a nd T yroler, quoted by Cassel, 1975 ); 5 1 co mmuniti es were ra nked according to th eir d egree of mod erni zation a nd a stra tifi ed random sampl e of m en aged40- 49 years was examined . Th ere a ppeared to b e a _good associa tion b e tween th e d egree o f moderni zati on a nd th e preva le nce of hypert ensiOn. However, Norman-Taylor a nd R ccs ( 1963 ), in th eir New H ebrides survey, did no t fin_d a ny ri se o f bl o~d. pressure in th e m ore moderni zed a nd accultura ted group compared with th e m ore tm ditiOna l g roups. An interna tional compa rative study was und ert a ken a m ongs t three Negro rura l p opula ti ons in .Ja ma ica, T he Ga mbi a a nd Tanzani a using sta ndardi zed prevalence survey m e thodology (Vaugh an a nd Miall , 1977). The J a m aican p opul a ti on w as near Kingston, th e capital, a nd showed mean bl ood pressure levels close to those from m oderately d evelop ed communiti es in N igeria (Akinku gbe a nd Oj o, 1969) a nd Ugand a (Shap er a nd Saxto n, 1969 ), a nd to those of E uropeans. H owever, the p op ul a ti ons in Th e Gambi a a nd Tanzani a were rura l subsistence farmers in a reas where very littl e d evelopm e nt had occurred , a nd here only th e fema les showed a small rise in old er age groups, th e m a les

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CA RD IOVASCU LAR D ISEASES IN DEVELOP ING COU TR IES

show ing no ri se at a ll. Coronary hea rt di sease a ppeared to be very ra re in a ll three studi es but rh eum a ti c heart di sease was co mpa ra tively frequ ent. Th ere a re very few co mmun ities th a t ha ve bee n well studi ed a t different tim es in their own d eve lopm ent. On e trend that has bee n well d oc um ented , but whi ch is of d oubt fu l validity, is th e rise in th e preva lence of hyperten sion in Uganda around th e nort hern shores of La ke Vi ctori a, studi ed in successiv e surveys. Donni son ( 1929 ) fo und no case of persistent ly ra ised blood pressure in two years o f examinin g labo ur recruit s a nd \ \'illi ams ( 194 1) found no sig nificant ri se of b lood pressure amongst a mixed assortme nt o f clinic a ttend ers, outpatien ts a nd peop le at vill age ga th e rings. Howeve r, Shape r a nd Saxton ( 1969), working in a nea rb y popul a tion, found blood press ure levels for eac h age group simi la r to th ose for Ame ri ca n wh ites, w ith 23 % hav ing hy pert ension (:;> 160/95 ). Ca sci ( 1975) qu o ted th e ri se in b lood pressure leve ls found in P a lau , but not in Ponape, in the U .S. Trust T err itori es in th e Pac ific since d evelopme nt occurred in P a la u followin g th e Se ond W orld W a r. Some fac tor, or fac tors, a ppea r to ' protect' th e peo ple of Ponape but no t those of P a lau. Th ese a rc probably th e best co ntroll ed studi es of rep ea ted cro ssec ti ona l d a ta on th e sa me co mmuniti es, but th ere ccms to be a n a bsc n c o f good longitudin a l data on individu als in suc h co mmuniti es.

MIGRA NT STUDIE S Studies on mi gra nt g roups who have moved is an accepted tec hniqu e a nd gives th e bes t res ults when co mpa ri sons ca n be mad e be twee n those who have moved away a nd th ose who hav not (Cassel , I 974) . Thi s approach is helpful in lookin g a t ge ne ti c and env ironm ent a l co ntributio n s but the opportun it ies and dra wbacks a rc ma ny a nd have bee n di cussed for ardi oresp ira LOry di sca es by K aga n ( 1970), who po ints out th a t mig rant s ma y be a v ry different type of person from tho e who did not move away . In ca rdiovascul a r di sease a classic mig rant gw up stud y was ca rri ed out on J apanese living in J a pa n, H awaii and Californi a . Th e in cid e nce of CHD roe (in th ose who had b n r sic! nt for many yea rs) higher in Ca liforni a th a n in J apa n, with H awa ii int ermedial , a nd th e r verse was tru e for th e incid e nce o f strokes, whi ch rem ained hig hes t in J apa n (Gordon , 195 7). Compara tive studi es on migrator y g roups moving from ' primitive ' to developin g soci ti s arc few, but tend to show th e d evelopme nt of higher b lood press ure levels a nd a n in erea ing in cidence of CHD as the mi gra nt g ro up becomes 'wes terni zed' and accultura ted. East r Isla nd ers who had migra ted to Chi le a nd th n re turn ed were found to have a st eper ri se of blood press ure levels in rela tion to age, a nd esse nti a l hypert ension wa detected in mig ra nts but n tin the stationa ry isla nd ers (Cruz-Co ke et al., 1964). In a stud y of rura l a nd urba ni zed Guatama la n Indi a ns hig her bl ood pressure levels were found in th e a cultura tcd g roup, a nd this was on ly pa rtia lly ex pla in ed by grea ter body mass (H oob ler eta!., 1965). A group of nom adic Ni lo-Hamit ic Samburu tr ibesmen from nor th ern Kenya were studi d a ft er th ey had joined the army a nd a ft er a few yea rs th ey were fou nd to hav ra ised blood pressure levels and increased weight when omparcd w ith their nomadic ntrols (Shaper et al., 1969) . F lorey a nd Cu ad ra do ( 1968) carri ed out a blood prcssur survey of a pe V erdeans still li ving in th e islands a nd another a mongs t immi grant dcsc nd a nts living in New Eng land, U.S.A. There were lower levels amongst the isla nd ers, but th difli r nc was not ignifican t a fter a djustm ent for difli re nces in weight. Th ey ascribed the differ nee in blood pressure levels to weight a nd no t to environm ent a l factors. Another a pproa h is to examin e ea rly and late arrivals in a mig ra tory mono-e thnic group . A group of Yemenite J ews who h ad lived in Israe l for m ore th a n 30 years was

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compa red with a group of more recent a rrival s and wit h a general sa mpl e of th e I srae li popul a ti o n. The CHD ri sk fac tors of obes it y, bl ood pressure levels a nd se rum c ho les tero l were g rea tes t in the Isra eli s, nex t in th e lo ng-stay Y c m cnit es a nd leas t in th e new arri va ls. Th e a uth o rs conclud ed th a t thi s represent ed th e impac t ofw cs tcrn-sty lcd soc ieties (Brunn e r et al., 197 1). By exa mining wh ole po pul a ti ons before indi vidu a ls c hoose to mig ra te a nd th en fo ll ow ing th e sta ti ona ry a nd mig ra tory g ro up ove r time, d a ta for the in c id cn c o f ca rdi ovascul a r d isord ers can be o btain ed wh ic h is m ore sound th a n by using o nl y p1·cva lc nce measures. Th e T okel au Atoll Stud y in Polynes ia w as a b le to d o just thi s a nd it s findin gs sugges t th

A review of cardiovascular diseases in developing countries.

Annals of Tropical Medicine & Parasitology ISSN: 0003-4983 (Print) 1364-8594 (Online) Journal homepage: https://www.tandfonline.com/loi/ypgh19 A rev...
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