Journal of Epidemiology and Community Health 1992; 46: 127-132

Social network and activities in relation to mortalityfrom cardiovascular diseases, cancer and othercauses: a 12 year follow up of the Study of MenBorn in 1913 and 1923

Lennart Welin, Bo Larsson, Kurt Svardsudd, Bodil Tibblin, Gosta Tibblin

AbstractObjective-The aim was to examine the

relationship between social network andactivities and causes of death.Design-The study was a prospective

cohort study of middle aged men examinedin 1973 and followed for 12 years.Setting-Gothenburg, Sweden.Subjects-The subjects were 769 60 year

old and 220 50 year old men who hadparticipated in a health examination.Measurements and main results-Main

outcome measures were mortality fromcardiovascular diseases, cancer and othercauses. In multivariate analyses cardio-vascular mortality was related to baselineblood pressure (p<0-001), smoking habits(p = 0 002), myocardial infarction or stroke(p < 0-001), and a low level of social activities(p = 0 04). Cancer mortality was related toage (p = 0 003) and smoking habits(p = 0-001). Other causes of death wererelated to poor perceived health (p = 0 02)and a low level ofhome activities (p = 0 004).In univariate analyses the above risk factorswere strongly related to all three causes ofdeath. In addition cardiovascular mortalitywas related to age, a low level of home andoutside home activities, few persons in thehousehold, and poor perceived health.Cancer mortality was related to poorperceived health, few persons in thehousehold, and a low level of socialactivities. Other causes of death wererelated to living alone, poor perceivedhealth, and a low level of social and outsidehome activities.Conclusions-Well known risk factors for

premature mortality like smoking, hyper-tension, and major cardiovascular diseaseare verified. Middle aged men with a good"social network" (here measured as a highlevel of social, home, and outside homeactivities) may be partly protected againstnon-cancer mortality.

The social environment, measured as socialsupport, social network, or social activities, hasattracted a considerable amount of interest duringthe past decade because of its possible role as aprotector against various diseases and prematuremortality.' 2 Most of these studies have beencase-controlled studies with their inherentdifficulties in disentangling whether poor socialsupport contributes to disease causation orwhether disease leads to poor social support andnetwork (for review, see'). There are, however,

several prospective studies in which poor socialnetwork has been linked to an increased mortalityduring follow up.> l" These findings may indicatethat a poor social network is one factor ofimportance in disease causation in humans.A poor social network seems to influence

morbidity and mortality in a general way and isprobably not linked to any specific diseaseoutcome.' In the Honolulu Heart Study12 noassociation was found between social networkscales and the incidence of coronary heart disease.In the Alameda County Study the "social networkindex" was associated with mortality fromdifferent causes of death including cancer,coronary heart disease, and other cardiovasculardiseases,'3 again indicating a non-specific effecton mortality.We have previously shown that the level of

social and other activities is inversely related tomortality during nine years of follow up amongmiddle aged men.9 Follow up has now beenextended to 12 years and in this report therelations of various social network measurementsto mortality from cancer, cardiovascular diseasesand other causes of death are presented.

MethodsSTUDY POPULATIONIn 1963 a random sample of 50 year old men (allborn in 1913) was drawn from the populationregister in Gothenburg (n = 973) and invited to ahealth examination. Eight hundred and fifty fivemen (880o of those invited) participated. Tenyears later, in 1973, a new sample of men born in1913 (60 year olds) was drawn including all menfrom the 1963 sample who were still alive andliving in Gothenburg and men who had movedinto the area since 1963. This sample consisted of945 men out ofwhom 787 (830) participated in amorning examination and 769 (81 0,,) in anafternoon examination one week later. Inaddition, we invited another random sample ofmen born in 1923 (50 year olds). Out of the 292men invited, 226 (7700) participated in themorning examination and 220 (7500) in theafternoon examination.Men participating in the afternoon examination

in 1973-74 (n = 989) form the study population ofthis report. All these men also participated in themorning examination.

EXAMINATIONSThe participants came to the morningexamination after fasting overnight. Blood wasdrawn for serum cholesterol determinations andblood pressure measured in the right arm afterfive minutes' rest in the seated position.

Section of PreventiveMedicine,Department ofMedicine, OstraHospital, S-416 85Gothenburg, SwedenL WelinDepartment ofMedicine,Sahlgrenska Hospital,University ofGoteborg, SwedenB LarssonDepartment ofFamily Medicine,Uppsala University,SwedenK SvardsuddB TibblinG Tibblin

Correspondence to:Dr Welin

Accepted for publicationApril 1991

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Questionnaires about smoking habits, alcoholconsumption, and previous stroke or myocardialinfarction were completed. Smoking habits werecoded as 1 = never smoked, 2 = ex-smokers,3 = smoking 1-4 g/day, 4 = smoking 5-14 g/day,5 = smoking 15-24 g/day, and 6 = smoking 25g/day or more (1 cigarette= 1 g tobacco, 1cigarillo = 2 g, and 1 cigar= 5 g). Pipe smokers'consumption was calculated from number of 50 gtobacco packs/week. Alcohol consumption wascalculated from the reported frequency ofdrinking and the quantity and type of alcoholconsumed. 14 Reported cases of myocardialinfarction or stroke were verified from hospitaland outpatient clinic records.The afternoon examination included a detailed

questionnaire about various activities which wascompleted with the help of a psychologist. Theparticipants were asked about their marital statusand number of persons in their household.Questions about activities during the past year(table I) were divided into home activities (10items), outside home activities (14 items), andsocial activities (8 items). There were threepossible responses; no (score = 0), occasionally(score=1), and often/regularly (score=2). Theratings for each question were totalled to give atheoretical range for home activities of 0-20points, for outside home activities of 0-28 points,and for social activities of 0-16 points. Theparticipants were also asked to grade their healthon a seven grade scale ranging from excellent(score= 1) to very poor (score= 7).

FOLLOW UP AND CLASSIFICATION OF CAUSES OF

DEATH

All participants have been followed up until theend of 1985 with respect ofmortality with the help

of newspaper obituaries, parish registers, hospitalrecords, Statistics Sweden (the Central Bureau ofStatistics), and a re-examination in 1980. Followup with respect to mortality was 100,,. Causes ofdeath were coded according to the Internationalclassification of diseases (8th revision 1965). Forthe purpose of this report the causes of death wereclassified in three groups; cancer (ICD code140-239), cardiovascular diseases (ICD code 390-458), and all other causes of death.

STATISTICAL METHODSStatistical tests were done by comparing each ofthe three groups of causes of death with thesurvivor group (excluding the two other groupsfrom the analyses). Student's t test and the x2 testwere used to analyse differences in mean valuesand proportions. The correlation coefficientspresented are Pearson or Spearman correlationcoefficients. For multivariate analyses, thelogistic regression technique was used. Allstatistical tests were two tailed. Analyses weredone with the Statistical Analysis System (SAS)software. l5

ResultsDuring the 12 year follow up period until 1985there were 215 deaths (22" ,), 63 from cancer, 122from cardiovascular diseases, and 30 from othercauses. There were 190 deaths (25",) among the60 year old men and 25 deaths (11 O,) among the50 year old men.

UNIVARIATE ANALYSESAmong the three traditional risk factors forcoronary heart disease, systolic blood pressurewas higher and smoking was more prevalent

Table I Home activities, outside home activities and social activities. Possible responses; never or no (score= 0>, occasionally (score= 1), anldoften/regularly (score= 2)

Home activities

RepairsHobbies (eg stamps, photography)StudyingReadingGardeningPainting, carpentryBoatCarSauna bathingExercise bicycle (indoor)

Outside home activities

Swimming, bathingCycling, skiing, skatingHunting or fishingMushroom or berry pickingCinemaTheatreConcertsSport eventsHorse racing eventsRestaurant diningMuseums, exhibitionsTravelling abroadTravelling in SwedenChurch attendance

Social activitzes

Parties at homeOrganised sports (soccer, handball, etc)DancingVisiting relativesVisiting friendsTrade union meetingsOther association meetingsStudy circles

Table II Traditional coronary heart disease risk factors, social network, activities, and health in relation to various causes of mtiortality during12 years offollow up

VariableSystolic blood pressure (mm Hg)Smoking, pointsSerum cholestrol (mg'0,)

(mmol/litre)

Unmarried (" )Number of persons per householdHome activities (points)Outside home activities (points)Social activities (points)

Cancer den=63Mean

148 43 51t2516-49

23-82 05t6 927-264-55t

eaths Cardiovascular Other causes Stirvivorsdeaths, n = 122 of death, n = 30 n= 774

(SD) Mean (SD) Mean (SD) Mean

(25 1) 155 2§ (29 0) 139 3 (25 2) 142 9(1-42) 3 11* (1 59) 3 03 (1.63) 2-78(47) 256 (48) 244 (53) 249(1 22) 662 (1-24) 6 31 (1 27) 640

(0 63)(3-92)(3 62)(2 22)

23-82 14t5-80t6-97t445§

(0-76)(3 42)(3-58)(2 36)

Perceived health 2.87* (1 61) 3 03§ (1-76)MI or stroke before examination in

1973-74 (",,) 48 21 3§

MI = myocardial infarction. Tests for significance were done compared to "suvivors"*=p<005; t=p<001; t=p< 0*01; §=p<O00001

4333t1 77§4-33§5.77t4.33*3-41t

(0 77)(2 76)(3*55)(2 32)

(1-82)

3.3 26

(SD)(22 8)(1 49)(46)(1 19)

(0 89)(3-52)(3*57)(2 23)

(1-43)

17 82 377 097.995.33

2 39

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among those who later died from cardiovasculardisease than among survivors (table II). Smokingwas also more prevalent among those who laterdied from cancer. Men who died from othercauses did not differ from survivors with respectto coronary heart disease risk factors (table II).

Marital status did not differ between survivorsand those who later died from cancer andcardiovascular diseases. Among men who diedfrom other causes, 4300 were unmarried(divorced, widowers or bachelors), a significantdifference compared to 1800 among survivors(table II). Men who died (irrespective of cause)lived in households with fewer persons than menwho survived (table II). Men who died fromcardiovascular diseases and from other causes hadsignificantly lower scores (points) for all threetypes of activities compared with survivors, whilemen who died from cancer had significantly lowerscores for social activities only (table II).Men who died had perceived themselves as

having poorer health (scores were higher) thanmen who survived (table II). Previous myocardialinfarction or stroke before the baseline exam-ination was more common (21-300') among thosewho died from cardiovascular diseases thanamong survivors (2-60,, table II). Conversely the50 men with myocardial infarction or strokebefore the examination had a higher cardio-vascular disease mortality (52°o) during follow upthan the other 939 men (10bo, p<0O001).

Figures 1-3 further illustrate the gradedrelationship between the factors that werestatistically the most strongly related to the threecauses of death. Cancer mortality (fig 1A) waslowest among non-smokers (1.50°,) and wassuccessively higher among ex-smokers andmoderate smokers. Heavy smokers had thehighest mortality (104%0). Those living inhouseholds consisting of 1-2 persons had highercancer mortality than those living in largerhouseholds (fig 1B). Participants with low scoresfor social activities (fig 1C, 0-3, lowest quartile)had the highest cancer mortality (10-60o), while

10

8-

6-

4-

2

0

Figure I Cancermortality during 12 yearsoffollow up in relation tosmoking habits (A), thenumber of persons in thehousehold (B), and socialactivities (C). Univariateanalyses.

Non Ex 1-14g 15g/day /day

Smoking habits

4 3

participants with scores above 3 (the three highestquartiles) had approximately the same cancermortality (4.9-5.7o0).

Cardiovascular mortality (fig 2A) was lowestamong men with systolic blood pressure of 140 orless, 8 7-6 90o (the two lowest quartiles), andincreased successively to 18-90 among men witha blood pressure of 160 or more (the highestquartile). For social activities (fig 2B) there was agradual increase in cardiovascular diseasemortality with decreasing activity from 8 2%0, to18-60°. Participants grading their health as good(fig 2C, scores 1-2) had the lowest cardiovasculardisease mortality, 98"0 -7 8"0. With lowergrading of health there was an increasingcardiovascular disease mortality to 15 100 (grade3) and 17 700 (grade 4 or more).

Figure 3 illustrates the three variables with thestrongest correlation to other causes of death. Forhome activities (fig 3A) there is a successivelyincreasing mortality from 0-5 to 5-70. withsuccessively lower levels of activity. Number ofpersons per household shows a similar relation,those with four or more persons per household(fig 3B) having a mortality of 1- 100 whichincreased successively to 9. 30 , among those livingalone. Mortality among those who graded theirhealth as good (fig 3C, scores 1-2) was 1 600. Forgrades 3 and 4 or more, mortality was 4 3(0 and5200o respectively.The 60 year old men had significantly higher

blood pressure and smoked less than the 50 yearold men. Their marital status did not differ from50 year old men but the 60 year olds lived insmaller households (data not shown); 60 year oldmen also had significantly lower points for allthree activity variables than 50 year old men.Mean values for home activities were 6 57 and7-79 respectively; for outside home activities 7-46and 8-77 respectively; and for social activities 4-95and 5 80 respectively (all significant at p < 0 00 1).

Neither frequency of drinking nor type oramount of alcohol consumed was related to any ofthe three groups of causes of death. Total alcohol

=1 w771777,

Persons in the household Social activities

20

15-

10-Figure 2 Cardiovascularmortality during 12 yearsoffollow up in relation toquartiles of systolic bloodpressure (A), socialactivities (B), andperceived health (C).Univariate analyses.

0

140 159

0

I0@

LISystolic blood pressure (mm Hg) Social activities

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310 7-9 5-6 0-4Home activities Per(

consumption, expressed as gram alcohol perperson per year, was not related to any of the threegroups of causes of death (data not shown).

INTERCORRELATIONSThere was a highly significant correlation(r = 0-44-0-53) between all three activity variables(table III) and between the two social networkvariables marital status and number of personsper household. There were significant correla-tions also between these two variables and theactivity variables (except between marital statusand outside home activities). Smoking did notcorrelate with any variable except for a negativecorrelation with blood pressure. Blood pressurewas negatively correlated with the number ofpersons in the household and social activities.The possible confounding factors (see below) of

perceived health and myocardial infarction orstroke before the examination were correlatedwith each other (table III). Poor perceived healthwas more common among unmarried men andamong those living in small households or alone.Poor health was also strongly correlated to lowscores for all three activities. Men withmyocardial infarction or stroke before theexamination also had lower scores for all threeactivities compared with men without myocardialinfarction or stroke (table III).

CONFOUNDING VARIABLES

Age is, of course, an important confoundingvariable since it is related not only to mortality butalso to almost all social network and activityvariables (the level of activity decreases with age,see above). A poor social network and low levels ofactivities appear to be important predictors ofvarious causes of mortality, but those already ill atthe baseline examination (higher scores forperceived health or previous myocardialinfarction or stroke) might be more isolated andless active due to the illness (table III) and theillness makes them more prone to death. This isevident from table II; men who died during followup perceived themselves as having a poorer health

09

1 2 3 34 >4 3 2

ceived health Persons in the household

than those who survived. Perceived health waspoorest among those dying from cardiovasculardiseases and other causes. Participants withconfirmed (and not only self reported) diseaseslike myocardial infarction and stroke at thebaseline examination also had a highcardiovascular disease mortality during follow up.Therefore, health status at the baselineexamination is an important confounder and mustbe taken into account when the predictiveimportance of the social network and activities isanalysed.

MULTIVARIATE ANALYSESThe logistic regression technique was used andonly variables significantly related to the specificgroup of causes of deaths in the univariateanalyses were entered into the equation. Since thethree activity variables were strongly correlatedwith each other (table III) only the variable withthe statistically strongest relation to the end pointwas chosen. Futhermore, each group of causes ofdeath was analysed compared to survivorsexcluding the two other groups of causes of deathfrom the analysis.

For cancer mortality none of the social networkand activity variables remained as significantpredictors (table IV). Age and smoking habits,however, were still related to an increased risk ofcancer death.For deaths from cardiovascular diseases, social

activities remained as a weak but significantpredictor (table IV). Stronger predictors ofcardiovascular disease mortality were systolicblood pressure and smoking habits, as well asmyocardial infarction or stroke before the baselineexamination.For other causes of death a low home activity

score as well as poor perceived health remained assignificant predictors (table IV).

DiscussionThis prospective study confirms the well knownrelation between mortality from cancer and

Table III Correlations (expressed as correlation coefficients, r) between factors significantly related to any of the three groups of causes of death

Systolic Outsideblood Perceived MI or Persons Home homepressure Smoking health stroke Married per household activities activities

Systolic blood pressureSmoking -0 15Perceived health 0 01 0 06MI or stroke before baseline

examination -0 01 0-02 0 20Marrieda - 0-02 - 0 03 - 0 14 0 04Person per household - 0 14 - 0 04 - 0 10 - 0 05 - 0 96Home activities - 0-06 - 0-05 - 0-22 - 0 11 0 27Outside home activities 0 01 - 0 04 - 0 18 --0 11 0-06Social activities - 0 07 - 0-05 - 0 20 - 0 07 0-16

MI= myocardial infarction'Married men were assigned score-- 1, unmarried men were assigned score = 0If r 0-07 then p<005, if r>0-09 then p<0O1, if r 0 11 then p<0001, if r)0 13 then p<00001

10-

% 6-

4.

2-

0

Figure 3 Other causes ofdeath during 12 years offollow up in relation tohome activities (A), thenumber of persons in thehousehold (B), andperceived health (C).Univariate analyses.

0-220 090 12

0-460 44 0-53

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Table IV Multiple logistic regression analysis of risk factors (significant in univariate analysis) for cancer deaths, cardiovascular deaths, and

other causes of deaths. Each group of causes of deaths was compared to the group of survivors

Cancer deaths Cardiovascular deaths Other causes of death

Regression Regression RegressionVariable coefficients SEM p Value coefficient SEM p Value coefficient SEM p ValueAge 0-221 0 073 0.003 0-053 0-033 011 0-036 0-048 0-45Systolic blood pressure - - - 0 025 0-004 0 0000 - - -Smoking 0 297 0-092 0 001 0-237 0-076 0-002 - - -

Perceived health 0-140 0-085 0 10 0-134 0-072 0-06 0-271 0 112 0.02Myocardial infarction or stroke

before examination 1973-74 - - - 2 415 0-361 0 0000 - - -

Unmarried - - - - - - 0-022 0 580 0 97Number of persons perhousehold -0-223 0 200 0 27 -0 072 0-148 0 63 -0 733 0 390 0 06

Home activities - - - - - - -0 206 0 072 0 004Outside home activities - - - - - - - - -

Social activities -0-096 0-069 0-16 -0-113 0-054 0-04The three activity variables were strongly related to each other. Therefore only the variable with the statistically strongest association to the endpoint waschosen for the multiple logistic regression

smoking habits.'6 In univariate analyses, but notin multivariate analysis, number of persons perhousehold and social activities were related tocancer mortality. This is explained by the agefactor since a higher age is related to lower levelsofboth these social network variables and also to ahigher incidence of cancer mortality.Among the traditional risk factors for coronary

heart disease, smoking and blood pressure, butnot serum cholesterol, were related to cardio-vascular mortality both in univariate andmultivariate analyses. All social network variablesexcept marital status were also related tocardiovascular mortality in univariate analysis butonly social activity remained as an independentpredictor after multivariate analysis.Other causes of death could not be predicted by

the traditional coronary heart disease risk factors.The social network variables as well as perceivedhealth were all related to other causes of death inunivariate analysis. After multivariate analysisperceived health and home activities remained asindependent predictors.We do not know whether our findings apply to

women also. In one study social isolation seemedto be a risk factor for total mortality amongwomen as well as among men3 but others4 5 havefound that women are less susceptible to a poorsocial network than men.

Social factors like marital status and level ofincome also influence the likelihood ofparticipating in a population study. Analysis ofthe non-participation group at the examination in1963 showed that these men were more oftenunmarried, and had more alcohol problems and alower income than the participants.'7 The non-participants also had significantly highermortality during follow up. 8 From these findingsone might infer that the impact of a poor socialnetwork on mortality is probably greater in thegeneral male population than is evident from theresults of this cohort study.The causal interpretation of the associations

between poor social relationships and activitiesand an increased mortality might be explained bythe "drift hypothesis". '9 Those affected bydisease drift downward socioeconomically andtend to lose contact with friends and relatives. Ourfindings partly substantiate this view since wefound an association between perceived poorhealth and a low rating for all activities. Also thosemen with objectively confirmed disease(myocardial infarction or stroke) had lowerratings for all activities. We do not, however, have

any longitudinal data on change in activities inrelation to change in health; thus the "drifthypothesis" remains speculative.The "vulnerability hypothesis" proposed by

Cassel20 might also explain our findings. Thishypothesis indicates that social factors or a strongsocial network (measured by us as an activityscore) protects against noxious stimuli whichmight otherwise cause disease and death. Wefound that men with high activity scores were lesslikely to die from cardiovascular diseases andother causes but not from cancer.Our data may thus support (and do not

contradict) the two hypotheses which have beendiscussed by House and coworkers in a recentreview:2' (1) lack of social relationships causedisease and death; and (2) sick people are lesslikely to maintain social relationship and morelikely to die because they are sick. Both thesemechanisms may be operating at the same timeand both increase the mortality risk.A previous analysis from this study9 supported

the theory that poor social support and a low gradeof social and other activities caused a generalsusceptibility to disease and death. Our presentfindings indicate that the risk of dying fromcancer is not affected by the social support and thelevel of activity. Susceptibility to fatal diseasesseems to be restricted to cardiovascular diseasesand other causes of death. With othermeasurements of the social environmentJenkins22 found that mortality from cancer amongmales (but not among females) was stronglyrelated to social and demographic factors likeliving in poverty areas, areas with smallhouseholds, and high divorce rates.Two other studies, one Swedish7 and one

Finnish,'0 have reported an association between alow index of social network and connections on theone hand and an increased risk of cardiovascularmortality on the other. The social network index ofthe Swedish study and the social connections indexused in the Finnish study were not identical to eachother and to our social activity score but includemany similarities like contact frequency withfriends and relatives and frequency of meetingswith associations. This contact frequency withother people might be the most importantprotective factor of the social network.We did not measure the quality of home,

outside home, and social activities. It may well bethat this quality offor example social participation(social activities) is more important than itsquantity as a factor of premature mortality. 1I

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This study was supported by the Swedish Heart-LungFoundation and the Swedish Medical Research Council(B90-27X-06276-09A).

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