epidemiological studies of hypertension in...
TRANSCRIPT
EPIDEMIOLOGICAL STUDIES
OF HYPERTENSION IN NEWFOUNDLAND
FINAL REPORT
PUBLIC HEALTH RESEARCH GRANT PROJECT #600-7 -10
Principal Investigator IAN E. RUSTED. M.D .. F.R.C.P .ICI
Co-Investigators E.C . Abbott. M .D , F.R.c .p .lel
J .G Fodor. M .D .• Ph.D I.R. Se nci •• t Ph,D .• A.RJ.C .
1. One tho~sand, four hund red and ninety-nine indi yi du~l s over the
age of 19 were studied in three N""fo~ndla n d fishing villages . nd
ina f ourth (control) mining and logging C01llnun i ty i n the centre
of the h l .nd portion of the Province .
2. Ked n sy, tol ic dnd dids tol ic p re,,~....,s of "'" les were hi gher i n the
th....,c fishing cOO111unities t han in the inland mining - loggin~
cOllrJlunity . The urne w.s true fo r femalc diastolic but not for
systo l ic blood press ure,.
3. The prcv~lence of hypertension, us i ng dge corrected scores, w.,
found to be hig,er in the Newfoundland fishi ng cor:rnunities than
~mo n g U.S . corrrnu ni t i eS surveYed in the U. S. Not ional Health S u rve~
and significantly abov~ an age and sex matched san:ple in the
lJIlitedKingdotl .
4. l fprev. l enceratesforroales.ndfe""'lc' • ....,cor:.hined,thehighe't
raU.s of hypertension (26 . 4~) were found in the fishing cotnnunity
of Fogo, wit h t he l owest r.te, in Badger , t he inl and corrr:1~nity (20 . 8~).
This compares with a lU prey"lence Nte i n the ~hHe popu l ation
s~rv~yed in the Nationa l Hca l th S ~ rvay.
5 . I n 1972, 479 indi viduals f rom age 10 to 19 ye~rs of age were
surveyed in Badger ~nd Fogo, 230 i n the fom-er a nd 249 in the
latte r cor:rnunity . The differences obscned jn thucar l ier adult
,uneyofbl oodpressure,re-.ppearedinthesurvcyofchildren;
the systol i c and diastolic prp.ssvres for both ~~l l e' .nd fem.le, ""re
s ignifi c~ntly hi ghcr in fogo than in B~dgcr.
6. Correlation ana l ysis of pressures in mothers and children showed
a direct re l ationsh i p i n Fogo but not Badger. InoothC()IIII1unities
therewH no cor..., l a t io n between bloOd pressures of fathers and
7. Analysis of variance of blood preHure scores of21Schild...,nwhll
at l east one sib l ing part i cipating in the rogo s urvey, and 197
children with at least One sibling in the Badger sruvey indicated
a highly significant s ibling clustering in Fogo. In aadger, the
tendency applied only to the systolic sco...,s. When parents were
added, the aggregation pershted in Fogo but oo t in Badger
lInalysisofbloodp...,ssuresof97adultsiblings liv in g in separate
households showed a siroilars ign ifi cance at t he 5% 1evel.
s. it is concluded that the family unit exerts an effect On both blood
pressure and body build . In Fogo, whe..., clusterlngwas roreexpl icit,
the genetiC]lOol was rore ho mogeneous than inB.dger. Some of the
differences (socio-economic,ellvironmenUll and nutritional) bet ween
the two c()llll1unities haw been examined . It is suggested that Some
of these fac tors (e .g . dieUlry) opcraUngduring the early life of
susceptible individuals rnoy have a li f e_long impact even i f the
factor does not continue to be present; lhe school/home environment
does not, in Hself,scemtoaffectbloodprcssurclevcls.
9. The sOdi"",1ntake measured 1n the four ( orm1 unities ,uneyed ranged
from 60- 300 " Eq/day (or 3 to 15 'Y" s~1t/dJy). Sodi lin i nt~~e
.. ~s l o"'!s t in Badger (122 • 39 1ft Eq) and highest in Fo go (157 • 48).
Th i s difference was statistically significant (p < 0.01).
Age and ~ex adjusted blood p~H ure scores in these two cOmlunities
followed the same. trend es thele.el of sodilll1 int.ke, i .e ., the
blood pressure values were generally higher in fogo than in
Bad9~r. In Badger , the~ was a statistically significant difference
in salt intake rehtionship (p 0.025) between first and third
and first and fourth systolic bl ood pressure Quartiles. In this
corrmunitj',thereisa posithe association between the level of
dietary salt intake and blood pressure le.els. There was nO such
~lationship in fogo, the salt intake being Similar in Nch quartile.
10. Mean blood pressu~ scores, with all fourconnunities cormined,
were higher in those with a rosHive family history of hyperten~ion .
In those with a Mgathe family history the mean blood pressure
scores were highest in the tertile with the highest sodhn intake.
Because of the high variance in bl ood pressures, the possibility
that these differences were due to chance cannot be confhlently
rejected.
11. Between 1973 and 1975,144 of the 210oroginal respondents in tile
dietary survey were re-assessed. The re-assessment inc luded a
co..,letephysicalexamination,re-measurementoftheBPlevelsunder
ncarbasalconditions,restingEKG,andadetailedinterviewabout
the medical history, present symptoms, etc. Based on t hese data,
t he group was devided into two groups of 93 verified "nonrotensi.es"
end 51 "hypertensives".
12. When theelectrolyteintale eHllb l ishedi n the 1968 survey
WIIS co..,ared in both groups, the results indicated that intake
of potass i um, cllldumaodmagnesium ... as lower in hypertensives
thaninnonro tensives-andthelevelsofintakeweresubstllntially
belo .. ~conmendeddal1y requiN.>ml,'nts in hypertensives . Salt intake
.. asMgherinnonnltensives(8 . 4~day) than in hypertens1ves (7.2
gm/day) . Itis possible thattl\e level of sodium intake may have
been sufficient , when accOll"4'anied by an inadequate intake of cations
(K+ , CaH, and HgH), to produce an increased p~va l enceof
hypertension in a predisposed genetically homogeneous popuhtion.
it is also virtual ly certain that, untll a few years before the
1961 survey, salt intake was considenbly higher in the three
coastal connunitieswhen heavily salted fish and meat were eaten
nlre frequently, i.e., beforerodern refrigeration and improved
transportation.
13. The results of the above studies, coupled with other data, strongly
suggest that the traditional nutrition pattern in the Newfoundland
population 1liiY be part of the web of causat1ve factors leadinoto
a high prevalence of hypertension.
14. The results of this project enabled the ossessrne~t of the proportion
of previously undiagnosed hypertensives among the studied
population. less than 301: of those .. ith diastolic blood pressu~
> 100 rmIHgwere receivingsorr.eformofantihypertensivetreatrnent.
Based on these data, a rodel ofa Colllllunity Control Program of
Hypertension .. as developed and is currently being tested in two
EPIOC~lOl0GlCAt. STUDIES
OFHVPERTENSIONINNEWFOl/NOlANO
PIJILICHEALTHRESEARCHGRANTPROJECT , 600-7-10
INTRODUCTION:
In the Province of N ..... foUf1dland. several lines of evidence h~ve suggested
that high bl ood pressure is IlXIre prevalent than in o t he r areas of Nortlt
America. Great Br i ta in or Ireland: (a) no.rrerouspractisingphysicians
throughout tI1e Province had confinned t hat high blood pressure was acolllOO n
find ing ; (b ) the results of an E-book t'orbidity Study conducted i n four
general practice areas within the Province suggested a hi gh prevalence of
hy pertension and its co~lications arong the reSidents in those areas It);
(c) t hese ifll' .... ssions appea r to be supporte d by rrortality figures which sho w
a high death rate attributable to cerebrovascuhraccidents in the Athntic
Provinces genera l ly and Newfoundland specifi cally (3).
tt;,tivatedbythisevidenceoneofthei nitialresearcl1projectsofthe
newly established Facult.Y of r.ed i cine of 1'e1OClrh l I..\"liversity of Newfoundland
was an epidemiological study of hyperte nsive disease i n New foundland . In
thi~ study attention was focused on four r ura l cOl!ll\un ities in Newfoundhnd
- Rarne •• Bay de Venle , Fogo and Badger (Fig. 1) which for centuries e~isted
1n relative holati on Mdwhere the diet of the people tradit ionally contained
a largoe qua nt i ty of salt . Heavily salted fish. beef and pori: were typic~l
COflllOnents of the everyday diet of rural Newfolllldl~nders until tI1e early 1960' s .
In the early 19£0's •• f ..... years before tI1ls study began, economic
transformation reS ulted in a ch.ange from sa lted fis h operations to fresh
fish operations i n Rarnea and Bay de Verde. Thecl1angewascofll' l ete;nRamea
and in Bay de Verde it was partial. Fo~ , on the other hand. large l y
maint~ined its salt fish operations . The inland cOlllnllllity of Badger re1llll ined
economically deP<'ndent on mining and lo99in9.
itwashypothesizeU that theseenvirom.ental _nd socioeconO.llic cha"'Jes fl\ ight
modify the p~tterns of mrbidity ~nd mrtality caused by hypertension 10
ltwos considered of particular iq>Ortance, therefore, toOlO'!asure the
lllagnitude of thls probl em and thus establish a baseline forfutureco~arison.
The aim of the first part of this project w~s to veri fy the ~ctu~l
prevalenceofhighbloodprcssure1nselectedareasoftheProvince.
This descriptive study was designed as ~ cross-sectional survey of the
adultpopulat1on in three coastal cOlllllunities and one lntandcollJ1lunity.
The second part of the project studied the chaNcterof the familial
aggregation of blood pressure levels in children and adults in two co ll111unitles.
Among the objectives of this undertak1ngwas an evaluat10n of possib Ie
geneticandenvironmentalinfluencesonthedistributionofthebloodpressure
The third part of the study focused on the diet of popuhtion s!fIl)les
in those fourcoomllTlities inwnich the initial survey was carried out.
The diehry intake of five electrolytes (Ii~. K, Mg. Ca ~nd Zn) was
determined and their possible association w1th blood pressure levels was
analysed.
Thefourthpartofthlsprojectaddressed.itselftotheex;stlnglevel
of treatment of hyperten~ive patients in rural Newfoundhnd.
We~re lnteNlHed inasscss1ng the proportion of previously undiagnosed
hyp~rtensives i n th1s popuhtion with a view to determining whether Or not
j~rovementSJli9htbepossible.
The reSulH of this study have led us to design further research
proposals which may I cad to primary and secondary prevention of hypcrten~ive
d"ea.e 1n the Newfoundhnd population.
fOOOR, J.G., ABBOn, LC. ~nd RUSTEO, I.E. An Epidemiological Study of Hypertension in Newfoundhnd. C"nadlon Medical flssociation Journall008:1365,(1973).
2. ROSS J., A Study of Morbidity in Family Practice. Can ram Physician IS: 105,1972 .
3 . HOIWI,K.,a ndFOOOR,J,G. UnpublishedP.esults.
LOCALE AtHl'IETlIOOOLOGY
The popul Hion sMlp le was drawn from fou r wld~ly separated
cOllf11unit iesinNcwfoundland(Fig. l).each havingatotJl population of
~ppro~im.Jte ly 1.000 . Based on 1955 Ce ns us s tatisti cs (1), tile tot~ l
populations were: Ra ... a: 1,160; Fogo : 1 ,150; Bay cle Vercle: 838; and
Badger: 1 ,192. The popuhtion of vot in g ~ge (21 ye~rs and over) in 1965
was as follows: 513, 592, 483 , and 522, respe~ tive l y. All residents in
t hese areas are Ca ucasians andthemajorityareofEnglish , $cottish
or Irish ancestry. Except for B~dger. which was sett led hte in the 19t1l
cent~ry, evidence exists tIlH til e origins of other towns wa5 several
centurlesear1ier,althou9'lpenll1lnent sett ler.lentprobablydid notoccurunti l
the 18th century. Fogo, R~rrea and Bay de Verde are fishi ng v111ages and tile
rMlo r ity of t he e",loy~d males derive tIle i r i ncolll' from the fis hery. Ranea
and Bay de Verde both haverroclern f .... sh f lshpJants.mlch etrl'loy a la rge
nunt>erofm.JlesandfeIllll1es . Forllllllesi n Badger.theprincipa l occupations
are mi ning and logging . It is close to an urt>~ n cen t re and tile Trans C~nada
Highway passes through the town. The populat1on 1n each to" n js re I ati ~e ly
static but there 15 sorne emigration , espechlly ~1T1.lng the younger adults.
Fogo and Rameaa .... situate d On smaller islands off the coaHand are
access1ble only by boat or phne.
"B10<.>dp .... ssure clinics" were held in each tow n within a one rronth
period duri ng the Auturmof 19£7 . Cl in ics were held fromlTllrning un ti l
evening in each town . I n Fogo, tile Out-Patient [)epa r tmentof t he Cottage
Hospita l was used . In Rarnea , t he baserr-ent of the Nurs i ng Station was used
and in Bay cle Verde, a local Parish Hall was used. In Oadger the ~rea "sed
was On t he second floor of t he ToWll Coun~il Buildin g, accessible by
cllntling a flight of shin, A d~ta c~rd on uch indi~idu~l .,us cO"l'leted
prior to tile examin~tion e~cept for detai I s pertaining to the indi vi dua I' s
IledicalandFaml1yhtstory. Hetghtwas recorded in incheswtthoutshoes.
and weight .... ~s recorded in pounds, in the least amount of clothing consi~red
C<)nvenient. so that no corrections .... ere deerred necessary for relMining
clothes. All blood pl"€ssures wel"€ rreasul"€d tn the seated position after
three to fiverninutes rest-Ouring this period further details of the
poersoMl and hmily history .... ere recorded by the examiner. Subjects w@re
aSked if they knew of farnllYlflenDers with "high blood pressure". Responses
o«>re recor~d as "yes", "no' , or "uncerhin". If the response .... ~s "yes".
the relationship was recor<led.
T .... oexarniners were involved In all blood pressure readings and
no apparent difference in interpretation of diastoltcor systolic press ures
was noted bet><een the two. To reduce obserller bias and digit preference,
all bloodpressures .... ere recorded on one of two sphygrrornanorreters of the
London School of Hygiene and Tropical l'edicine(2). Clip-ontypecuffsw@re
usedw1th the above instruments.
The fifteen subjects .... howere unable to attend the Clinic in
Ra~awere seen at nome where their blood p...,Hure was 1fIe4suredwith a standard
sphygrrornanolfle ter . The two sphY\JTPlMnometers used On al l other subjects
halle ~1 re~dy been shown to be well suited to epidemiological studies
because of avoid~nce of observer bias and digi tal prefe...,nce (3).
sys tol i c blood p.-..ssure. Ph.se IV (change intone prior to dis~ppear.nce)
andV(pointofdisappearance) were recorc!edas the diastolic pressure. In
th i s report the Phase V diastolic blood pressure was considered for al l
analyses.
The survey of the ~dult population was co,"" lemented in 1972 by
examination of the blood pressure levels ofchlldren and youth ran9in9in
age from 10-19 yearL Two h""d"..d and thirty were examined in Badger and
249 in Fo'}O.
Two blood pressure neasurements were taken On each child at
approximately 15 minute intervals . Data was also obtained on body weight,
height,armcircl.Ollferenceandpulserate.
Age and sex adjusted scores introduced by Hamilton et al (4)
were ..sed to render the collected dolt. co""aNble. OtherCO""utationswere
made ",ingstandarddeviation ""its (SOU), introduced by Kass and Zinner (Sl.
The SOU· x - ~ where x is tile observed blood pressure value and i i$ ~
tile mean value of thecorrespondingage-andsex-gl"Oup . Thus,theSOU
enables us to determine whether the blood pressure un der consideration
differs~rkedly from the average In tIlatcategory .
RESlA.TS
Sa!T!llinqRates
A total of 1,499 (a l0fe~les and 689 N.les) persons over the
age of 19 we"" seen during the inlt1l1 sttidy*. Using the 1966 Census data
one estimates that from 60S to 90S of the population we".. covered by the
Survey. The response rate of females (Table 1) was generally satisfactory
for drawing valid conclusions (particuhrly in Bay de Verde). The response
rate of males (Table 2) was less satisfactory, as in the case of Bay de Verde.
SOllie of the male inhabitanhwere ",available at the ti me of the survey
because their occupation necessitated frequent periods away fl"OlIMllne.
nUllbersH~l ed'n eachage9rouPlnshown tn Ftguns 2 and 3.
l'Iean8loodPnssunsRelatedtoAgeandSex
ftguns 4a and ~b show the "'un systolic and dtastollc blood
pnssunvaluoesforstxdecades.forbothsexes . tneachofthefourtowns.
ValuoesforthoseSOyearsandoverwenexcludedbecauseofsmallnUll'bers
In each of tne four towns. Anlncnlsetnmeansystolicanddlastoltc
pnssunwas noted with tncreaslngageuptotheageof70-79.after
whtch then was a tendency forbloodpnssun levels tostabtltZ1!.
lnelcn town,systoltcpnssunswenhlgnerln .... les than In
fell>llu In the 30 - 40 age group. However. tn the older age groups, the
bloodpnssun levels of fellllles exceeded toose of males. and with the exceptio n
offogo.showedasteepergradtent,wtththe dfffenncbeing ma tnt.ltned
Only .. lnordiffennceswennotedbetween lllll le andfe..alediastolic
pnssunswtthnoconstanttnndtohlgherpnssunslnfe .... les. Systolic
anddlastollcbloodpnssun values of males frolll Bay de Verde IndRaroea
wen located betwen the hlltlest val\les tn F09l and the lowest tn 8adger.
Theulll' tnndwas discernible for fl!lWl le diastolic but not forsystoltc
bloodpnssuns(Ftgu,..,.,4b). (urves ford;'stoltcpnssuns tended to be
parabolic and the gradtent was sl _Ilar for the four towns and betwen the
"Hypertenston " PnvalencelJsI"qYarious Crtterta
Table 3 shows the age adjustedpnvalence ra tes forrespondenU
with "hlll bloodpnssun" and "borderline blood pressuN!" . tn the four
surveyedconllUntttes.
The cut-off points for the two above lllentioned ClUlgortes wen:
160"," Hg systolic Or 95 .. Hg diastOlic ~nd 140 ... Hg systolic Or 90 1ft Hg
Diastolic, respectively.
Prevalence rates for ' hlg, blood preHure" lias higher for feroales
(27-30%) than for lWl les (14-l71) In three towns. InFogo,the ratesllereequal
for lWllesandf~l es(261 )asCOlllParedlllthBadgerllhere the rateforf~les
lIasthesamebutonlyI4.lIInJMles.
The "borderline" pre~sures" lIere, IIlth the exception of respondents
In Fogo, higher for IIIIIles (23-271 ). All three flshlng cOll'JllUllltl es h~d
significantly higher rates than those found in the U.S. IIhlte populatlo n
Role of Body Stature
Tables 4MdS COlIIPare the Broca !nde~ values for females and
lI'ales In the studied comunities. Obesity lias IIOre frequent in femln ;
theprevalencerangellasbetweenl3-XlI . Theanalogo usproportionsforllo11es
range between 10 and 131. Although,as expected,the bodyweight generally
showed a Significant correhtlon to the blood pressure levels (Table 6),
it can only 1Io1~IIIo111y upla!n 231 of the variance In the group IIIth the
hlg,est calculated valueofr-O.49l {Badger, females less than 40 years
of age).
The association between the body weight and blood pressure was of
littl e or no sl9l1if1cance !n lil Ies less than 40 years of age.
OISCUSSIOH
In his review of the geographic distribution and etiological
factors of hypertension , Epstein (7) reported that therellu lWIrl<ed
skepticislllintheepidemiologicalcollllunityofstlidiesco..,arlngblood
pressuredistributionsindifferentarels. Epstein felt that "The sl..,lest
*Srocllndex: Standardwelgllt In(9- helgllt In em Minus 100. Deviations above and belOll are Indicated by plus Or Minus values: underwelgllt(-6or n)re); normal weight (-5 to+S) ; oYenft!lght{+6to+l5); lWI l"tedlyoYer--..elgllt{+16orllllre).
~pprod~". taken by some . is to say that all these differen~es are fi ~titloos .
and due to non-~o~arable or careless techniques In blood pressure measure
mentand nonrepresentattveSdfl'1lll ng. lIhi1ethese factors enter into the
picture. it is rrr.>re likely that true popuhtion differences <Iouist" .
On tIlebasls of our data (hble3),weconc1ude that the prevalence
of hypertens ion is indeed higher in Newfoundland than armng the ~o"..,arable
white!>OpulatloninNorthAmerica . ForfelM.les the prevalence rate (as in
the case of Ramea) waS alrrr.>st double the reported prevalen~e rate of 15S for
U. S. white females (see Table 3) . The prevalence rate for males was
higher In Newfoundland than for white U.S. males . It Is also noteworthy
that the !Ilean blood pressures were higher than those observed in U.S.
studies. Analysis of age and se~ adjusted blood pressure scores also Indicated
tIlattllebloodpressu!,)"valuesobservedintheNewfoundlandruralpopuJatlon
were significantly ~bove blood pressure levels of an age and se~ matched
safl'1l le in the ~ltedKingdom (8).
fromtheresultsobtainedthereseemtoberegiona] varlations'n
the prevalence of high blood pressure In Newfoundland In that valuesWl!re
hi!11er arrong the coastal fishing co rmllmltles than In the inland mining and
logging town of Badger. If the prenlence rates forrTIIIl es and ferTIIIles are
contllned,thenthehi!11estprevalenceofhypertenslon Is noted in F090.
The validity of our findinQs is supported by an I"dependent study
whl~h cOfl'1l~red the II>lrtal1ty due to cerebrovascuhr stroke (eVA) in Newfoood
land with the rest of Canada (6). The standard rrr.>rta l ity ratio of eVA ' s was .
found to be approximately XIS higher In NewfoundJand than in tile rest of
Considering those hctors which could ~ontribute to the observed
pattern of blood pressure distribution, two areas were e xamined.
1) The nl1eof genetle heton.
2) Theinfl'-'E'neeofenylronment.
The following tvo parts of this report ooa1 with these tvoareas.
-13-
~ l'ICiiRF.l ·
NEWFOUNDLAND
PAR T I
f~malu a&~;::: 19 yur.
Badger
hyde I'erde
Fogo
PART I
T~e cote ~f poctlclp.nlon of the nd"lt p"p"lotlo" ~f four 1I""f~Yndl<l"d co .. -.. "nltl~ " In t~e blo"d pressure . "r~e y
~y ~~" Mid c.-unitiu
F.XAM(N~O
00. ,
PART I H'1:
100 FOGO
AGE GROUPS
PART I l'i<:'1 J
AGE GROUPS
---~~--~.
PART I FisJ' 4b
BAY DE VERDE
"" RMI(A BAOC(~
;'
.-;:/( ].'(1 _ 't
R .... o.' (c)
fo~o (0)
\lhit", -lio n.·hit.,
!J . O 21.8
17 .8 15 . 2
"hIgh . Sys(nllc ? l.;n '" d\~,t"1Ic ~95;
16'l
1.'> .1 n.1
n',",lerl I,," TIlu"d rrc"~"rcs
12.5 12.1
BQrderllrte - S~ ~l "j;, h,· t,;eert 100 ~nd HQ or dl~'lol!e b"l". ~n 90 ,00 95.
PMT ~
logo
'~'r.c,l ""er"Cjl'ht
>40yro ..
>.Oy ....
P~RT .!.
AIJJI:STED (OnSERVETl/J:XI'ITTFn)
RATlDANnEJ.IlODPRESSl1Rl
C('Erf]CIENT "f C'lRIIU.ATW·'
tevel of ~ lot r. t(o,'l "lr.nHica~,, ~ : ~\~
" ,ogo fe",~les 40 ye~", n - ~6 40 y~3r5 ,, - lOS Fogo ,.., 1.,. 40 ye.'r~ n - 75 40 years ~ - 78
8ad~H f~I!1 .~le. 1<0 ve.us n - 99 BaJgcr ,"~l,,-s /,0 ye", ~ n _ 86
40yMrs n - 99 1,0 y~~rs n _ 71
I. Ce~sus of Can-ada. Catalogue 92-632. Statistics Canada, 1968.
2. ROSE,G.A ., Holland,W.W., and Crowley. E.A. Lancetl:296,(1964).
3. T1BBLlN, G., Aurell,E., Paulin, S. , andSanne, H. HighBlood Pressure and Hypertensive Oisease in Hen Bom in 1913. In St.!Im1er, J., Stamler, R. andPul1l114n,H.T., The Epidemtology of Hypertension, first edition, Hew York: GruneandStratton, p.428,(1968).
4. flAHILTOO,I1 ., Pickering,G.W .• Roberts.J.A.F.andSowry,G.S.C. The Aetiology of Essential Hypertension. ClinicalSclence 13: 37,(1954). ----
5. !(ASS, E.H. and Zinner, S.H. Haw Early Qm the Tendency Toward Hypertension be Detected? Ml1bankMerrorialFundQuarterly47: 143,(1962).
6. HOGAN,K.andFodor,J . G. Unpublished Results.
7. ~PSTHH, c . H. and Eckoff, iLK. The <:ptdemiul091 of Hi~h olood Pressure-GeographtcDistributionsandEtiologlcalFactors , inSt.llmler,J., Stamler,R. andPullman,H.T., The Epidemiology of Hypertension, flrstedition, New York: GruneandStratton, p.155,1967 .
8. HAMILTON,I1 ., Pickering.G .W., Roberts,J.A.F ., andSowry .G. S.C. (1954a). "The aetiology of essential hypertension . I. The arterial pressureintilegeneralpOpulatioll. " ~. ~.,13.11
THE iNFLUENCE OF THE FA.'IiLVON
BlOOOPRESSURfLH£LS
Of tne fourconnun!ties surveyed, the 9reateH contrast In
prevalence of hypertension was found toexhtbet\<jeen Fogo and Badger. It
wasrieclried.therefore,tou.ndertakealRJrerietalledanalysisofthesltuation
In these t\<jo corrmunltles. Two specific research qcoeHlons were posed:
1) Are tI1e observed differences in blood pressure levels
between the adult populations of Badger and Fogo
obsenable in youths andchl1dren:
2) Is tI1ere any observable pattern in thedlstrlbutlon
of blood pressure values in each of these corrmunities?
In order to answer the above questions. In 1972 we conducted.
survey of youths andchlldren 10-19 years of age in Badger and Fogo.
n!thodsuseddurin9thissurvey~reasdescribedon?a!JlE!s7andB.
RESULTS:
The original differences in adult blood pressure values observed
In the survey carried out In 1967-6Bln the two corrmuntHes reap~ared In
the survey of children. As can be seen in Table I, the systolic and
diastolic pressure for both males and feMleswere significantly hillerin
Fogo than in Badger. Aswastl1ecasewitl1theirparents,tI1erewererlO
differences between tI1ecOIrrnun\tles in mean bodywelllU, height and pulse
rate in tI1e corresponding age and sex categories.
There also appeared tobea pattern to tI1e distribution of blood
pressure valLJes in Fogo. In this comnunity people"ith elented blood
pressures tended to be clustered in certain sections: no such patternw as
app.rent In Sadger (1). Recent surveys (2, 3) Indicated tI1at blood pres$~re
valLJes c.nb .... ggregatedin·hyt>ertensive families' lnd this posslbtlitywas
uplored.
Correlation ana1ysi5 was perfOrrT"ed for blood pressure values
between husband and wife pairs, however, no association was foun dineither
cmrmunity . It was postulated that if hmlly ~nvin:mrnent was a factor, its
effectwouldonlybecorneapparentafterthecouplehadlivedtogethera
lengthy period of tirne. Thus, since the divorce rate was neg1igibleand
ageatTMrriagewas fairlyunifonn, the age of the wife W4S taken as an
indicator of the length of the TMrital relationship . Ltsingonlythe45
famllies in which the age of the wife was 50 years or older, a statlstlca l1y
s i gnificantcorrelation(r·.29S)wasobtainedforsystolicbloodpressure
values of husbands and wives in Fogo . In Badger, for the 33 families in
which the wife W4S over 50 years of age, the blood pressures of husband 5
andwhesvariedinilependently(r - .020j .
The corre lation Of blood pressure scores between husbands and
wives with longer marital histories in Fogo, but not in Badger, CQuld
either be caused by sOralenvironrnental condition (which would roost prob ably
be tirne relatedj Or it could be a statistical artifact . However, if this
pattern were to persist when chi1drenwere analyzed, additional credence
couldbeplacedontheexplanationthat5~environmentalfactor(socia1,
psychologica1,dietary,physica1,orgeneticjwasoperatinginFogO.
The first item evaluated in this regard was the correlation between
blood pressure of pare nts and children. In Table 2 the correlations of
systolic blood press ure between rrothers and children and between fathers
and chl1dren. both in FogO and in Badger, are presen ted . The results indicate
that there is a direct relationship between maternal and chlldren's blood
pressure in Fogo, but not in Badger. In Fogo, theroother's systolic press ure
accounted for 12Z of the variance of the child ' s blood pressure. lnbotll
COrrJllunities there ~p~ared to be no correlation between blood pressure
values of fathe~ and theirchtldren.
An an~lysis of varhnce of blood pressure scores of 215 children
witn at least one sibling participating in tne survey In FOgo, !nd 191
childrenwHh at least one sibling in the survey in Badger, was conducted .
Clll1drenwere included in this !Mlysis whether or not their parents were
The Fratios, as shown in Table 3. indicate a highly signiftcant
sib ling clustering in F090. while in Badger the trend only held for tne
systolic scores. WhenparentswereaddedtocolT"4)letethefamtlyunit.tl!e
aggregation ~rsisted in F090but not in Badger.
In oroor to further elucidate the nature of the famlltal clustering,
the blood pressure levels of97 adult siblings (age2:19 yea~) living tn
dtfferenthouseholdswerestudiedusingtdentlcalstatisticalmetnods.
As is shown inTable4,bloodpressure levels of adult stblings
sttll displayed a similarity,whichwas signtffc!nt!t the5J level.
It is widely accepted that increased body mass is associated with
elevated blood pressure; in addition. it should be remeJrbered that nO
differences were observed in mean height and weight for these 00 cOrmlunittes.
Thus. height and wetghtwere examined as facwrs which mtghtexplatn the
observed pattern in blood pressure. Analystsofvartancerevealedthattn
Fogo, weight and height tended to be clustered in fa.,iHes (F ratios of
3.169 and 2.398. respectively). \lhi1e tnls pattern was repeated In Badger,
ltW!s not as pronounced. in8adger.tneFratio5were2.6Jlforweight
and 1.804 for height. Thus,aswttnbloodpressurevalues.tnerewasa
tendency for clustering In botn cOlmnmitles. This analysis. however . did
not reveal1f the famili@sinwhich there was hi~ body mass were too sarre
as those wi \11 high blood pressure 5cores . This step required a correlation
ofrrean family hei~t andrrean hmlly .... eight .... i\11 mean bloodpreHure .
Since the data on these variables .... as in standard devi4tlon units. it .... as
f:>05s1bletoobtainfamilymeansonallthre@. SpearmllnRankOrdercorrela-
tion5wereperfonnedand\11el"{'sultsare shown In Table 5.
In Badger. both helgh·t and weight tended to vary independently
and high blood pressure was associated wi \11 families who were heavier but
notnec@ssarilytaller(l.e . families .... lthatendencytowardobesity).
From the pattern In Badger. it appeared that high blood pressul"{' existed in
tMse famll1es .... l1ohada largerrreanbodymass.
it can be concluded that the faml1y unit exerts an effect on both
blood pressure and body build. From our data. at th15 stage. 1twas
difficult to judge whether itwu predominantly the gerletlcor theenvlronme ntal
co""onentwhich was operative in the phenorrenon of blood pressure andb ody
build clustering families. In Fogo. wI1ere the clustering was IOOre explicit.
the genetic pool was mud, IIIJre hOrn:)geneous than in Badger. However. there
.... ere other profound differences between these two cOlll11unities such as soc1o -
economic. environrrenUl. and in part. nutrltional factors.
The Shared environrrent. as well as genetic hctors. may account
equally for the similarity of blood pressure levels in these families.
One can theorize that if such external factors .... el"{' operating during
exceptionally susceptible periods urly in life. the iq'lact.,ight be lifelong.
even if th~ factor did not appear to be pres~nt. Observations lllilde i n
experlrrenUl hypertensicnmodels suggested that high salt intake has such I
"orodusoperandi" in rats (4,5).
Shared horne environrnentof adults cIoes not seem to visibly
influencebloodpressureleveTs. There were bro findIngs In tilis survey
which led uS to this conclusion:
1) The blood pressure levels of husband andwHe pairs.
'~e scrutinized in great detail the correlation of blood pressure
values bet><een husband and wife 'pairs in each of the fourcorrmunlties.
The only Hatlstically significant correlation was found in Fogo.
and only in tilose families where the wife was over 50 years of age. A
closer lool revealed that this fact was due to the increased frequenc yof
husband and wife pairs having reTatively low blood pressure levels as colll'are d
with that expected for their age and sex group.
A simihr pheno<renon was observed by Sackett (6) who analyzed the
Framingham material. We concur with his belief that the observed association
was spurious and was caused by the hct that marriages. where one of the
partners was hypertensive. were rore li~ely to be dissolved by death. Thl$
would oot be the case for those ctluples who were "nonrotensive".
~) The blood pressure levels of the adult siblings reseobled those
of their blood relatives and not those with whom they shared a
cOl!'mlnhoU'Sehold.
Welllilyass~thataninteractionofenYlronmentalandgenetlc
factors in infancy and early cIllldhood had pre-detennined the furtherdev elop-
ment of blood pressure levels and that the presence or a~sence of those
factors inadu1t life had only a limitedilr"act.
Sincenutritionisoneofthemainc~nentsofman'senvironn!nt
and a substantial nurmer of controversial reports exist about the passible
infl uence of COrTmJn ~~ 1t i nt~ke on blood pressure levels of hUlTldn populations
thts problem w~s ~n~lyzed in greHer detail in the third part of thts report.
1-' '-'" .. , .. '
,~
.. d,.r ,~
ALl. 00 SEI.IJWSTED 111.000 ""[SSORE \tORES j" '1"1 J«wroo.'<OLlI.~
_illES , (~n DI"" ~~(I 'fI)lln/S '0
".'.:.11
Fogo
B~dger
PARTIr
CO£FF Ie IIIIT OF CORRELATIO!1 B[TW£[II S~STf'lllC nLOOO
PRESSUR£ l[VElS OF PARENTS Aim C1IllDREII III
T~ IIEI:FOUIIOlAIIO COW-tulilTIES '
r - O.3S2
p 0.05
.: 8100d pressure v~lues compared to StandHd Devia t ion IInlts (SDU).
r; .... berofchlldren In Foqo · 125 . Numbero f families·44 .
• II"mber of Children In BadQer • 129 . lI .... ber of faMilies • 5~ .
PARTJ..:!
AIII.lYSIS or VARlAiIC£ OF TH£ BLooO PRES~U~E
HI CII!LOR£N 10 - •• ?f) YEARS OF Ar.E
S!A.SIRRELAT10N5H!1'
Fogo-SystolicB.P.
~etween f~n1il ies
fogo-OiastolicB . P.
Badger-SystolicB.P.
~etW!!en famll ies
With! n f~mll! es
Bad9Cr" -Diasto1icB .P.
Within familIes
p < 0.01
.. p < .05
I}<>qreesof
Sum of Squares
95 . 652
113.865
223. 209.5OS
11'
72.642
52.803
99.8B5
152 . 689
Square
1.347
FRatio
1.798'
1.0304
Between Siblings
Within Siblings
Between Siblings
WltMn . Siblin~s .
PARl IT
~t~\.1UF_Y~E.I_~!l.f_L!1£_!!!U_L9(1(} PR[S2!:I..R~
gp!!!?S!QJ.r!.1.QU...,}~.I@!._A!~O_.!!.!.l!!!..~
8QI!.~SlBlI!:~.!....!1l fOGO
P<O.05
HeiQht
Systolic
Height
Ohstollc
Pressure
Weight
with
Systolic
Weight
with
Ohstolic
PARI !l
R~tn: OROER (fIRRELATII)tJS FOR HEAN FflMIL Y
HElr,IITI,'IDWEIGIITIIITHMEArIFMILYBLooorRESSURF
,301
S19 " .09 sigs .01
,205
siS" .06 s19 - .05
,319
si9- ,005 Si9"
,281 ,322
Si9 - .01 siS"
1. AUERDlCE, \~. II ., Fo<br, J .G. and CCrson , L. N. A ~cth:xl for the Determin"l ion of Cl\lslering of High Bl ood hesstlre Va l ues . Proceed;",!" of U", 65th Ann!",l C~nadian Plblic ll("lth A",:oc;lItion ~, p.-.ga283 , J'-"""'20 , (l974).
2 . HIW;JoJ sn:IN, \~ ., Kantor, S . , IbrahiM, M. and Sackett , O. L. Familial Ag::j«><.Fltion of In~ t>rCl;.sU(C. ~ 195 :160 , (1966).
3 . HlIYES , e .G., 'l';roler, Il. A. and Cassel , J .e . Fami l y liggrsJa tion of Blood Pressure in r:vans County , Georgia . An:h , tntcm . B:d 128 : 965 , (l971).
4 . Ci\HL , L . K. effects of Qlrcnic !::<cess Salt Ingestion - E:q:erir.ent.al Ilypcrtcnsion in the Rat : Corrcl.<ltion with III""Vl Ilypcrtcnsi.cn , in Stamler , J ., Stamler , R. and PullIr.:m , N. T . , 'Ille EPidemiology of HyP£ICtcnsion, first edition, NeW York, ~ and Strllttoo , p . 2lS , (1958) .
5. ~n=.Y, G. R. TIle ~riment.al ~idemiology of Scdiun Olloddc TOxicity in the Rat , in StMUcr, J . , Sta1t"~er , R. and Pul lIr.:m, U. T. , ~nip)ogy pf Hyr&rtensjoo first edition, I:",,· Yo rk : Grune and Stratton, p . 240, (196.? ) .
6 . =rr, D. L. Blood Pressure Correlation in Spouses , in Epidemi.ology o~ Hypcr:"1ISion . Proceedings .of the Ccrlferenc:c on l lypcrtensl.On 1 74 . F. ,lor: P . Cg" lesby , Olicago.
low salt diet WH the only effettive therapy of hypertension
until the nineteen fifties. Wlththeintroductionofawidevdrietyofanti-
hypertensive drugs, the pradisingphysichn paid less (or no) dttention to
dietetk therapy. Continuing reseu'Ch in thls field wn motivated more by
scientific than pra'1'kltk reasons, although the ~ssjbi1ityofa high salt
inta<e being associated with the prevalente of hypertension inNe..f oundland
was one of the factors which firHled to these studies.
There are numerous reasons why there has been a recent increased
Interest in this problem. AIro ng these are the following:
1) The,.., is a growingawa,..,ness that a lifelong drug treatment
IsnotacceptabletoasubstantialproportlonofhypertensiV1!
patients. Thishcttsbestm.Jnifestedbypoorc~lhnce
with thetherapeuticregimen(l,2, 3).
OJ iilemagnltudeof the problem in the cor.rnunHy precludes a
satisfactory solu t ion based on individual management. The
best hope fora decisive turnabout in the presentsHuation,
as far as the morbidity and mortality caused by hypertension
is concerned, h primary prevention. Nutritionallntenentlon
practica l posslblHtyofprtrn.J.rypreventlon(4) .
A review of the present situation In the "salt and hypertension"
field is therefore justified by more than academic renons.
The abundance of salt in the everyd~y diet is ~ rehtlvely new
occurrence. [)uring the phylogenesis of m.Jn, sodium 1~t~ke waS ",lnl"""l,
probably not more than lO-15mEq per day. Upuntllaboutthe19thcentury ,
salt was a relatively SCarCe and highly prized cOO1'l'lOlllty. Salt improved
the palatibtlityof food and sometultures ntribed to It a mod elevating
effect. hnong Shvic nations, the custo.o of offering bread and salt to
guests was a gesture of reverence. Its ... tderavai1abllltyandHsusefor
conservation of food led to vastly increasedconsl#lption. ThissHuatton
was parttculHly prominent in Newfoundland,..tJere salting fisn and beef were
tNdltioMl methods of food preservation.
Sincethebeginntng'ofthe20thcentury,therehasbeenspeculatton
about the possible role of dietary salt Intake in the etiology and
patkogenesisofhypertension.
In 1904. MOard and 8eaujard (5) detnOnstrated that restriction
of salt In the diet could reduce hypertension. Kempner's (6) low-sodll.-,
rlce-frultdiet, popularized In 1940 .... as the first 1arge sca1e. sue cessfu1
attempt to reduce blood pressure of hypertensive patients bynutrltiona 1
intervention. Shortly thereafter, other Investigators reported that
high salt Intake could induce or aggravate el evated blood pressure levels
Inpatients. Thesec]lnlca1 observations stimulHed experimental resean:h.
which led to the hypotnesis that a direct causal relationship lllay ex 1st
between salt and hypertensive disease. [);ahletal(7)delllOnstrated that .
In the laboratoryrat,a highly susceptible strain can be identified
which develops hypertension with Increastngsalt tntake. Theyhavealso
5h~thattheyoungertheanhllalatthethnettwasfedh;ghsaltdlet,
then"(lre raptdwas the development of hypertension (8). Even a short
exposure fora period of two to shweeks to the high salt Intake In
early life was capable of producing a permanent elevated blood pressure
(8). Thesefindingsonexperillll!ntalhypertenstonwerelaterexpandedand
conftrmedbya n...aber of other authors (10,11,12) .
However, whe~ attempts were .. ade to extrapolate these experime~tal
fi~din9s to h\llllll~ populations, they were met with some co~troversy.
O~ Table I are listed those better ~~Oto~ aut~T$ who have
loo~ed at the possible association bet..een sal t consumption and
hypertension. The authors In the left column of this table all found
positive correlations between the level of dietary salt intake and t he
prevalence of hypertension In a vartety of different populations . Thus,
a reasonable body of data exists to suggest a~ association of salt
conSll11ption andl1ypertension between populations (13,14,IS, 16,17,18).
A nl,l'l'tJer of studies haveatteqlted to show a correlation within a
population between sa1t Intake and hypertension. Arn:lngthesestudles
wereonesoonebySnecklothandhlscolleagues(19) in the West !ndies and
[)awtler and his co-authors (20) i ~ the Framingham study. However , these
researchers did not find anyassoclatlon between the urtnary sodita
output and blood pressure levels within the study papulattons. On the
otl1erhand,l-tlallandOlc\ha_(21)observedanlnverserelationshipbetween
the urinary output of sodi .. and hypertenston in their Soutl1 Wales surve y.
COnsidering tI1ese controvershl reportsandthei~rtMtpractical
Iqllicatlons of this proble. it was decided to evaluate the relation
Of tI1e dietary level of five electrolytes (Na,I:,Ca,l1g&Zn) in four
soo-saqlles of the general papulation in the rural areas of lIewfoundland .
~:
!n the first part of the survey carried Out fn 1967-68,asaqlle
of sixty individuals in each of the fo~r towns was selected to be
included in a dietary study. These groups consisted of reSidents who
gave an assurance of cooperation with the study ~nd a<flerance to the
protocol . An attempt was Illi!OO to have ~pproxirnately equal nurooers of
edeh ~ge group and ~ b3hnced co~sHion of the sexes. C~reful efforts
were maoo not to reveal the purpose of this aspect of the 5tudy and
thus avoid a orodHic3tionof the diet on the part of the respondents.
There were two ~urvey periods, each l asting seven days . The first
period was in the winter and the sHond in the s...rrner . Of the 240 persons
chosen, 210 cOlTl'leted the first survey . One hundred and twe nty-seven
respondents p.rticip~ted in the second survey.
Participants prep~red daily ·ph.ntom" diets which were placed in
individual one gallon po lyethelene jars. Each nDrning all food
collectionsof thepreviousdaywereweighedandhorrogenizedina
Waring blender. Onehundredm1aliquotsofthehorrogenatewere
rerrovedandfrozen. The electrolyte content In aShed samples of the
food was determined from these. The sodh.,. and potassillll content in
the food aliquots was measured by f l ame photometry wi th lithium as the
internal standard. The di etary zinc, calc1l1T1 and magnes;lITI content were
estimated for all samples by atomic.bsorption spectrophoto...::try.
Acc urate collec t ion of food samples was insured by daily visits to each
house by a dietician.
RESIJ..TS:
Figures 1,2, 3and4111 us tratedallyvarlatlonl n sodl".,.l ntake
for four Individuals. It was necessary to sttidy these four individuals
over a period of seven days inoroorto t3ke into account the dally
variation of sodium Intake . Despite this varhtion the mean ln t3ke
for these seven days was remarkably similar for the two seasons of tI>e
year , winter and surmer. The r~nge of measured sodjllTl intake was between
60-300mEq/day,cQrrespondingapproximatelytoadletaryultintakeof
-43-
3-ISg/day.
Table 2 shows the mean and standard deviation values of the
sodium intake in the fourcolTJllunities studied. Thesodill/llintakewas
lowest in Badger (122 t 39) and highest in Fogo (IS7 i48). Thls
difference is statistically significant (p,O.Ol). The fact that the
inland town of Badger had the lowest sodium intake may reflect tlle
kindofi"l'acttMtthecons~tionofsaltedfishhashadontheother
threecoaHal cOlTJllunities. Itis interesting to note that the next
lowest mea n sodhnn intake was found in Ramea which cO"l'letely changed
its salt fish processing operations to fresh fish operations in tlle
early1960·s.
BaydeVerde,whichprocessesbotllsaltfishandfrrshfish,had
a hi9hermean sodium intake than botll of tlle cOIIJIIUnities mentioned above
but was lower than Fogo, whiCh had tlle highest mean sodillll inUke. As
was pOinted out earlier, Fogo still maintains a predominantly salt flsh
opention. These figures may be dellXlnstrating the effect that social
and economic changes have had on tlledietetichabits of tlle people
residlnginthesecor.Tnunities.
ltlsalsointerestinqtonotethatinthef:w{)lOOstcontrastinq
cOlll11unities,tlleaqeandsexadjustedblood pressurescoresfollow tlle
same trend as the level ofSOdillllintake (Table 3).
Ilalesineachcolll11unitywerefoundtohavehighersodill:llintake
than females, but the differences were not statistically significant.
There were no significant differences in sodill/ll intake between
respondents with low and high values of the Broca index. As can be seen
in Fig. 5. the mean values of the sodiumconsu"l'tion in each of the
connunitieswas lower in the lowponderal index" group. This probably
reflectstllefactthattlleserespondentshadaIOWl.'rfoodcons~tion.
In assessing the relationship between corr ... :mHlt intake and
casual blood pressure leve Is, cOl1l'arisons were made arrong four Q~arti les
(lowest to highest) of systolic blood pressure distribution in the
two cOOlllooities ~hown to have a statiHically significant
difference in sodium intake (Table 4). These COl1l'ariscns revealed that
tIlerewere statistically si?nHicant rehtionships (p.:O.025) between
the fit>tand third quartl1e as well u between the fit>tand fourth
quartile of tile systolic blood pressure distribution and corrm:m salt
intake in the cClI'IIlunlty of Badger (Table 4) . ~o such statistically
significant relationships were found when thesarrecol1l'arisonswere
made On dllta obtained from the corrmunity of Fogo.
Effect of Positive FamllyHistory:
history of hypertension aroong fit>torderrelatives from those who had
a negative family history and tIlen cOl1l'are tile mean blood pressure
levels expressed In age and sex adJusted scores in three tertilesof
saltconsul1l'tion. The results of this analysis are presented In Table S.
T-.ro trends are discernible from these data :
a) Ther.lE!an blood pressure values are higher In the group wi til
positive family history ;
b) intnegroupwithnegativefaml1yhtstory,thell"@anblood
pressure values were highest in thehighesttertileof
sodiumconst.qltion.
However, since the variance of blood pressure in tIlese family
groupswashigh,thepcssibilitythat thesedifferencesweredueto
chance cannotbeconfl<.\ently rejected.
ltwasrealisedthatcasualbloodpressurell"@asurementscouldnot
wHhoutquestlon be taken as an indication of the presence Or absence of
hypertensive dhease. Thus itw.s necessary to do a thorough clinical
evaluation of tile respondents. The next step, therefore, was to identify
those who could reliably be labelled as true hypertensives.
In the time I"'riodbetween 1973 and 1975. a re-examination of the
original group of 210 respondents from the fourcorrmunitieswhich
participated in the first dietary survey was undertaken . Of these
people, 144 were re-visited and a detailed examination was
carried out . This examination included:
(1)aninterviel<l;
(2) me.surements of body height and weight:
(3) a 12-leadHG:
(4}12-bloodpressureJleasurements-sixin
supine and six in se.tedposition afte r
a r.llnlrntJ1'11 of 't hour rest .
With regard to those respondents who had died during ti1e period
fol101o'ing the first survey, t/1 eir medical records and death certificates
were reviewed and based On ti1is evldence the blood pressure status was
assessed. Ulti""tely, we had a cOlI"4'lete set of infornation about 93
"normotensl""s· and 51 "hypertensives"_
Respondents accepted as hypertensives were those who had, during
ti1ewhole of the obsenationperiod,blood pressure levels of at leas t
160 rrm of Hg ~ystol1c and/or 95 nrn of Hg diastolic, or were per1lloJnently
receivingant ihypertensivetreatl'l('nt. The mean blood pressure level
of "nol"1llltens ive~· w~s 136 "'" of Hg systolic ~nd 78 II1II of Hg diastolic
wi V1 an average age of 45 years. The core,pondi n9 val ue~ for the
"hypertensives· were 175 nnofHg systolic and 103 nnof Hg dintolic
with an average age of 49 years.
The next Hep was to ucertain whether or not those respondents
who were classified as hypertensives did have a hig,er salt conS\llll tlon
Table 6 shows the average dietary electrolyte inUl:eand the
range of their variation as detenulned durlng the survey for the flve
electrolytes: Na. K, Ca . Hg andZn. The sodi llll lnUl:e for hyper
tensives corresponded to approxilllately B.4 gCDllmn sa lt per doly wMle
the nonrotenslves cOnlS lm!d about 7.2 9 of cormr,m salt per doly. As
indicatedlnthlstable.thecoeHic1entofvariation .... asO.30 .... hich
lndl~tes that the vari ation of sodi lm jnta~e arrong individuals .... ithin
the hypertensive and nonootensive groups respectively was not excessive.
in addition, thedletarycons~tlonofpotasshlll,lMgnesl Ull and
cal clllllwas lower among t/lehyper tenslves as cOllflared .... lt/l the nonl'l)
tensives . Zinc .... as the only cation which was const.medmore by the
hypertensive group. These values were surprisingly low, s ubstanthlly
belowthelevelrecolm'endedbytheCanadianOietaryStand.JrdBureau,
The following procedure .... as used to further analyse the difference
insodiurn consUIIfltion between nonrotenslves and hypertensives in t/le
fourconmunities(Table7).
Each difference In saltcons lIIIption between nonrwltenshes (H)
andhypertenslves (H) was weighted by the reclprocal of its variance ,
l.e.thewelghts .... ereW . l/(SEofdiff.j2, inooalestheweighted
averagedlfference .... as 33.38 with a stand.Jrderrorof 11 . 155 between
the salt consllllPtlon of the norwotensives arid the Jlypertensives, t .e.,
thehypertensivescons~sI9n1flcantlY.l!!!s.i1tthanthenonootensives.
This relationship was not so clurcut in the fema)eresponde nts . For
them the weighted average dHfHence was 5.396 with ~ standard error of
6.848. This gave a Z-ratio of 0.79 which was not statistically
signi fic~nt. Thus, it was concluded that salt const.lllption was lower
in the hypertensives than in norrrotensives and this difference was
highly significant in males.
Also ,theNa/KandNa/Caratiodidshowaninverserelationship
to the preYdlence of hypertension in ma les and a positive relationsh ip
with hypertension in females. See Tables 8 and 9. Thesedifferences
were not statistical ~y significant.
DISCUSSION:
Du r findings as far as theinter-individll<l.l differences in salt
i ntake and hypertension are concerned are in keeping with those
reported by MiaI! (22) and more recently by Berglund {23}. In this
study we did not find a positive associat ion between individual salt
intake and hypertension in a cross-sectional study of adult population.
We found an inverse relationship. Interestingly enough, it was
reported that rats with experimental hypertension given a free choice
ofeiti1er saline solut ion or water ingested signlficantly less saline
than norrrotensives (24). It is possible that we are actually observing
a similar "feedback"rnechanism in our population. This idea seems
plausible based on the results obtained (Table 4) in the two corrmunities
of Badger and Fogo. Only in Badger was there an observable gradient
within the corrmunity. in that the lowest quartile of blood pressure
levels had the lowestconslJ11ltion of sodium and as the constJlllltion of
sodium increased so did the blood pressure leyels. InFogonosuch
trend was observed.
lie would li~e to suggest that the trend seen in Badger may be due
to the susceptibility of the population in this conmunity to sodium
intllke, as opposed to the people of FogO .. ho have the hi~hest mean
sodilllll intake and. so have reached the pOint of ~odium Hturation.
COnsequent ly, no gradation in HIt intake corre~pondin9 to blood pressure
leveh is observed in this conrnunlty. Since there is still soemphysiological
physiologicallatitudepreservedforsa1tcons~tioninBadger, .. e
appur to have a dose response effect bebleen sodill11 intake and blood
pressure levels.
There is cOMincingexperlmenUl evidf,nce produced by Meneely an
associated (25) that a high level Of potdssium in diet can prevent or
arTl'!1 iorate the "hyper tens inogenic" effect of ~al t. Cal cill11 can exert
a ~imilar p",tective effect, as documented by Langford and Wahon (26)
.. hO basiully supported thenotionofa correlation between salt
intake and hypertension, even onan individual level. flc .. ever, these
a uthors proceeded to point out that the prevalence of hypertension
.. as inVersely related to the intake of calcium and potaHium. The entire
g",upofsubjects .. hich .. asstudieddisplayedanunusuallylowintake
of K,Ca,Mg and Znand in some cases theintake .. asclearlydeficien( .
Onlysodi ....... asbeing ingested at levels f.r.bove the physiological
requi rement - in n;lS t case~ 15 to 20 time~ above the requi red I eve I (27).
it is possible that .. ewere facing a sHuationsimllar to the above
quotedexperimetnsinourstudiedpopulation.
Ina population .. itha fairly horroqeneous genetic background and
·sensltized"hythelackofhalancingc.tions, the relatively high
sodi um intake may have eleci ted the "epidemic" of hyperten~ Ion in the
threefishingcOImIunities.
ltis also possible that the observed pattern ofelect",lyte
intake reflects other dietaryhablts Which facilitate the development
of hypertension. Recent reports fr(M'nSacks, RosnerandKass (2B)
-49-
indicatedthatvegetarhnshadal~rbloodpressurethans\lbjectson
mixed diets. In this study hypertension seems to be rehted to an
unbahncednutrttionanda relative ab!ll1danceofsodt~. Wecanweculate
further that thesocloecono.ic level and its inverse relationship to
the frequency of hypertension reported in a large mllrtler of U.S. studies
m.ly be Of relevance in the conmunities which we have studied.
Also. theeffectOfa deficient diet could be COqlOundedby the
lack of electrolytes in the drinking water- a situation characteristic
ofallfourconrn!ll1itiesstudied. Thedrtnklngwuer In each of the
studied areas is extremelysoft,containingless than ZIJPpmofCaCoJ .
These results have led uS to constder the posstbtllty ofa
nutritional intervention study. IfltcanbedelOOnstratedthatamre
baJanced dietlfOuld have an effect On tile level of blood pressure, then
anatte~ttopreventthedeveloprnentofhypertensivedtseaseinat
least a segment of the populatton un belll/lde by correcting thequallty
TAJV\fjASHIU9571
SASAKI (19621
SALT AND HYPERTENSION
I.ANGFO~O (19731
NOo,s"-'ClAlI<f<""'!I'l'lOSE 
DAILY SODIUM
JOO F - 12 dage 58
b -O-mean
. : ""~, """ 100
300 DAY DAY
mean
' - "0'9'61 _Ej __
.. t:.J. ",,,,, DAY DAY
SURVEY 1 SURVEY 2
)00
100
~
~
R • 12 « age 42
~~"-tJ- t!J DAY DAY
DAY DAY SURVEY I SURVEY 2
)00
PART III
flGURU
DAilY SOD IUM
B - 129 age 54
DAY
SURVEY 1
DAY
SURVEY 2
300
" 300j ~100
1j
f 100
o
~
~
DAilY SODIUM
R - 10 9 age 53
DAY DAY
R - 11 Q age 49
OAY OAY
SURVEY I SURVEY 2
Bay de Verde
Fogo
N£WFOU~OLANO HYP:::RT[~SION SURVEY
MEA~Na+ INTAKE ±S.O. mEQ..!DAY
1n±39
NlJ.IBEROFRESPONDENfS
01 .. 0011'0100<1 .... ".' •• ",... ".1 !oil
S,.ooltc.lOO<Ip, ... " ."., ••
01"'.It<.100<1 .... "" •• ,,,,..
-58-
TA8LE4
NetlntakelnStratifledSa~ 1 eofPopulatlonln Two Newfoundland COrmlunities (Badger and FogO)
by Quartl1es of Systolic Blood Pressure Distributton (Age and Se~ Adlusted Scores)
Meanua+intake 122*39 157148
'L...- P<O.OI -----1
N,' "' 1st quartile (lowest)
2ndquartl1e
3rdquartile
~t.' quartile (~jitc~t) 13!1.84t36 15~.54 t 39
Statistical Significance
of Quartl1es 1 vs II ! P~O.02S NosignHtcance
1 vslV P<O.025
NEwrOUNDlANQUYPERTENSIONSURVEY
HlTAlOFFOURCOMMUNlTlES
THE HlfLUEIlCE OF SALT INTAKE ON THE BLOOD PRESSURE LEVEL
BLOOOPRESSUREVALUESG IVENIN
AGE ANO SEX ADJUSTED SCORES
TERTIlES OF TIlE snOiUM HHAKE
MEOiUM NaC!
LOW NaCI
TOTAL
SYSTOllCBLOOOPRESSURE
(MEAN,!. STANO.DEV.)
FAMILY HISTORY
POSITIVE ~IEr.ATIVE
+12.1,!.40.1 ~ 18.3 ,!. 37.2
n - 58
+ 33.6,!.41.2 +2.I,!31.9
n-18 n - 53
+ 23.7!-39.8 +7.9,!34.4
n-15 n - 36
n " 36
+15.1,!39.9 +9.5,!34.9
..... IEWfOUNOlAltO ltvPUTtNsrON STUDY
M£ASUR£D INTAKf OF FIVE ELECTROLYTES 8Y OIAG~OSTIC CATEGORIES
/.\9
-61-
N[WFDUNDlANn HYPERTENSION STUDY
THE DIFFERENCE or SODIUM INTAKE IHN/fEN "NORMOm~::'1 VES" IN) AND
"HYPERTENSIVES" (HI IN 11 COMMUNITIES
/,1ALES (n· 75) rtr.1ALES (n " 98) Dlff. SE OF bTrF- SE OF
COMMUNITY IN·H) DIFF. (N-HI OIFF.
RAMEA 35.01 17. 49 -6.10 1l.08
FOGO 47.13 17:84 -17.14 14.18
BAY de Verde -44. eo 39. 83 15.20 11.19
DADGER 33.79 31.7D I.DI 8.79
~
'Ie.
NIl( so
.!'M!.J.!! TABLES
NHIFOU~!lLANO HYPE~TENS!ml STUOY
M/CA and riA/I( r~tios in the diet of "NOr"flXltensive"
and "Hypertensive" re5pondents
UJ:..U
~ HYPERTENSIVES
n " 37 n"17
6.91
2.20
3.75 3.32
0. 92 0.65
ELEMENTS
"10 C.
"I,
-63-
£M.!...ill TABLE 9
NEWFOUNDLANOHYPERTENSIONSTUOY
NAI CA a nd '~AI K rat I os I n t he diet of" No rmo tens I v e"
and "Hypertensive ' respondents
~
NORlIOTENSIVES HYPERTENSIVES
n - 47
6.35
1.40
3.13
0.50 0.62
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