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T 2 3-JUL-1994 14= 55 Dep.rtmeatof Epidemiology, 4ts Afihtazy Medical Univeriiey, Xi'ta, Cbina Y He, kcrvaer LS Li, proJsssor JYHI>ang,lWnMs Departmeat of Commuaity Medicine, Univesairy of Hong Kong, Hoog Kong z-H 12=. reader Department ofCordioloay, 4th Milltaty Medieai University, xi~an, ciina L S Li, projeamr R Y Du, yrvfeua. G L J'sa, PrMssscs J S Zbeng, laexwm. Corttspondence to: Dr T H Ism, Depanmont of Community Mediane. University of Hons iCoug. 5 Sassoon Road, Hong Kong. 8My199L":)8D1 380 44 71 495 3101 P.8o8/013 Passive smoking at work as a risk factor for coronary heart disease in Chinese women who have never smoked Y He, T H Lam, L S Li, L S Li, R Y Du, G L fia, J Y Huang, J S Zherlg Abstract Oblsrdpr-To study whether passive smo3dag at work is a risk factor for coronary Iteart disease. Desigte--Case-eo atrol study. Sattut~-Xi'an, China. Subjccia-59 patients with coronary heart disease and 126 eontrols, all Chinese women with full time jobs, who had never smflked cigaretrss. ..Rasultr-The crude odds ratio for passive smok- ing from huaband.eas 2'12 (95'/. confidence intervai 1•06 to 4-25) and at work was 2-45 (1-23 to 4-88). Zhe final logistic regression model, with passive smoking from husband and at work as the base, ineluded age, lsjstnry of}iypertension, type Apertonality, stndtotal cholesterol and high density lipoprotein cholesterol coucentrailons; the ad'yusted odds ratios for passive smoking from husbandand at.vork..ere 1-24 (0-56 to 2•72) and 1•85 (fl-86 to 3 •00) respectively. For passive smoking at work, statistlcally aigaificanc linear trends of increasing risks (for both crude and adjusted odds ratios) with increasing esposuses (amount esposed daily, number of smokers, number of hours exposed daily, and cumulative exposure) were obaerved. When t8est exposure variables wese analysed as continuous varfables, the crude and adjusted odds ratios were also significanL Conclusion--Pasaive smoking at work is a risk factor for coronary heart disease. Urgent public hesslth measures are needed to reduce smoldag and to protect noa-smo.kars from passive smoking in ~'.hi3a. ;nnroducdon Passive smoking has beca confirmed as a cause of lung cancer in adults a.ttd respiratory ill health in children,' but the role of passive smoking in causing coronary heart disease is still unsetded. Evidence that passive smoking is associated with coronary ha= disease is increasing. G+1anQ and Parmley reviewed the resulu of 10 epidemiological studies, together with physiological and biochemical data, and concluded that passive smoking causes heart disease.' The same conclusion was reached in a review by Taylor et al.' There have since been two caae-controi studies, both associating passive smoking with increased tisk of coronary heart d'iseaSe.• s As for the source of passive smoking, most previous studies reported assaelations with exposure from spouse exclusively. Of the 12 studies (eight prospective and four case-control studies) mentioned above, only two casccontrol studies presented data on passive smo]ang at work. In Britain Lcc u a! found no increase in risk for a combined index of passive smoking which included exposures at home, at work, during aravcl, and during leisure. This study had a small sample <:~.,r only 30 cases in mea and 36 in women.' In Australia Dobson st a1 found increaaed odds ratios for passive smoking at home for mea and women, but the odds ratios for passive smoking at work did not suggest increased risk-''fhi.s study had a Largcr sample, 174 cases in men but only 27 in momen. Stcc.uiand recenriy reviewed nine epiaemiologtical studies, pointing out that the lack of data on exposures to environnzenral tobacco smoke outside the home was one of the major weakaesses in the epidemiological evidence: G7sarz and Parmley also considered that the stitdies they reviewed underestimated the risk because exposures at home are generally smaller than exposures ataork.` In China, our earlier study on non-smoking women in Xi'an included 34 cases and 68 controls.' It found an adjusted odds ratio for passive smoking from husband of 1•50 (95% confidence interval 1-28 to 1-77). How- ever, this study did not include details of exposure for passive smoking at work. The present study is a second asrcottttol study which aims to study whether passive smoking at work is a risk factor for coronary heart diaease in women who have never smoked. It takes into account passive smoking from the husband and other risk factors. Subjeets and methods Tlu cases were patients with coronary heart diseasc (non-fatsJ, intadeat caxe) from the three large teaching hospitals of two medical universities in Xi'an betweea December 1989 and November 1992. 7Iu futal diag- nosis was myocardial infamdon according to WHO cziteria' or coronary stenosis confirmed by coronary arteriography. Coronary artetiography was performcd using Judkins's tcchaique'° and analysed by two experienced cardioradiologisss independently. The criterion of diagnosis of coronary heatt disease was a finding ofmorc than 50% occlusion in at Icast one of the major attaies. The agreement between the two radio- logists was over 90%. Patients with occlusion of 50°/* or less were ezcluded. The controls were from three sources: patients admitted because of suspected or diagnosod coronary heart disease but confirmed to be normal after coronary arteriography (no coronary stenosia at all); other medical outpatients attending cardiology depxrmsents (patients with psychosomatic symptoms, nienopausal syndrome, dysrhythmia, or non-cardiac chest pain); and a random sample of healthy subjects from a community screening programme for coronary heart disease. The latter two groups were confirmed to be free of coronary heaxt disease by WHO csiteria' atld~y normal exercise electrocardiography. A standardised questionnaire was designed to eollect~ inforttlation on demographic characteristics (such asN ethnic origin, age, residential history, edueationalCJZ level, occupation, and marital status); history of(Z hypertension, hyperlipidaemia and diabetes me7litus; ~ fsalily history of hypertension, stroke, and coronary heart diseAse; history of smoking and passive smoking ~ from husband and at worh; drinlong history; exercise; and psychosocial factors (such as Type A personality, ~ experience of mental trautaa, and saassful life evenrs). ~ The intetviews were carried out by three trained interviewers, before coronary arreriography for patients scheduled for coronary arteriography or diuing recovery for titose with myoeardial infaretion. '17se non-response rats was 8°/.. Physica3 exaalirrauoss followed standard me-t'taods HM,] vax.Ui,ia 308 51imsfvwxY 1994

20-JUL-1994 14:56 and included hcight, weight, body mass index, systouc and diastolic blood pressurc, chest tadiogtaphy, and dectrocardiography. Laboratory investigations included serum concentsstions of total cholesterol, triglycetides, low dcnsity lipoprotein cholesterol, high density tipoproteia cholesterol, and apolipoproteiQ A-i and B and tesss of liver and renal function. Only ethnic Chinese women who had never smoked (lifelong non-smokers) and who had a full time job were included (full time housewives, peasaats, and those who were tttired for five years or more were excluded). Passive smoking from husband was defined as siving with a amoking husband for over five years. Single women would have been considered as not exposed, but all subjects were found to be married. Passive smoking at work was defined as working with smoking coworkers in the same office or factory unit for over five years. Periods away from the work environment were considered as no esposure in the workplace. All subjects were found to be either not exposed or exposed for over five years. TAYLS='-4=hQ/ntk77R1Ct OfCuLS and Gi)1UMt No f•!.) No C)4) ofaw ofoooaata C6naawade (P-59) (n- 126) )e Pvi7as Ac= tywi+): K.~SS 19~ 61{s) ;056 39(66) 59(47) 6-26 0•04! M.rirat ~nws: Marfini 53(90) 119(94) DivoeeaA I (2) 2 Cl) Wlide,.od 5(9) 5(4) 1•60 "5 ooao.u.a ICK•„----t 16 cm ( 34(27) 31 ~ mScet » (~6) () 1-s1 0•47 sduonm (yoa+): 0-3 1(2) 1(1) ..a 15(25) 24 (21) 7 9 16(27) 34 (27) 1042 8(14) 33(26) *13 1902) 32(25) F-29 0-37 Twazta-Espoxwe oapmsfvrmakinaas 91 mmrols crndaata Ne(%) espo-d to No ('/+) pmlre exporcd w sumaking u" ~ lsufAwd at•sosic canav(,: No e«aasry uaioaspbyx osima he- d+.n.e(R.t,S) 2903) 21(3II) M;.dlsAO.ea., aa+as ma,osy Jx.es d>efte (a-26) 12(46) 8(31) C.-(a.59) 33(6f) 33(S6) rw=.e ar-Pa:eivs •mrkers feu., k,a3and and at awk and ovds addr rod•os emm arylra.t dueau cHee oaas ntio Noof Noof (9SS4coafideeos Y' ce,cs eoyo•o7a inta.i) (totreetsd) 9.,tue P.ni.a fmpldp, ¢om hutlNpd: No 21 68 t-00 Yes 38 58 2•I2(1-06ta4•25) l-TZ 0-030 PaNire Cnoiiaa at rork No 26 83 1.00 Ya 33 43 2•45()•23t04•ef) 7•02 0-008 r,.uzrv--Straafud aeolysis jorPauiae rno7m.t f,o,n Jt,udsrdand ar roork Pa%rve EMakm8 ca„d. odd3 rusio Noot Noof (9SS.eoafiemos €mm hu,bmd A[.vo[R wa coauol• mtasQ (eomaed) P YaBu No Ne Y e+ No No Ya Yn Ya 11 )s 10 23 50 33 1s 25 1.00 2-07 (0•781o 5-55) 2r53(0•82 to 7-e3) 4-18 (1 •63 ro i0•92) x' 1-91 2-42 9-i3 0.17 0-12 0-002 O"m!1 df-!. r-n9i. Ta•,[!ot tAxd: Y' •-i9-94. P•c4•00 i. 44 71 495 3101 P.809/813 ~.cwut~y .....~...~ .. recording of the interviews (for 10% of hospital subjects), interviewing the husband to vaildate the data from the wife (for one third of hospital subjects), and single blind reintecview by a second interviewer who was not awsrc of the Case-control sratus of the subjens (for 30% of hospital subjects). Furrheanore, 26 patie.nts had inizialiy been diagnosed as having coronary heart disease and were interviewed before coronary atteriography but were subsequently con- 8rnxed by coronary arcetiogrnphy to be normal. This group of "**aguosed" patients , was accepted as contxnis and their exposure to passive smoking was compsred with that of controls and cases who had not had coronary arteriography to check for subjective bias due to interviewers. Por the caleniation of sample size required, it should be noted that the crude odds ratio for passive smoking from husband found in our previous study was 3•0.• 1sslsming the proportion of exposure to passive smoking at work in the controls was 35"/., for a sigitifltstarz of 5%and a power of 80°/., 58 cases and 116 controls (one case to two controls) were required to detcet a cude odds ratio of 2-5. The data were managed and analysed by using the computcrpaclagea of Epi-Iafo (5.0) and srss-rc (3.1). Tha statistical procedures used iacluded rc, t test, x' test, )e teu for trend, and standard muitivariate techniques for unmatched case-control studies (strati- fied anslysis and multiple logistic regression analyris)." Tiu present study included 59 cases of coronary heart disease (34 were confirmed by coronary arterio- graphy and 25 sv;th myocardial iafarction) and 126 conttols (61 confitmed as negative on coronary arterio- grapby, 28 outpetients in cardiology depasttaeats, and 37 ftom community screening). Ages of ases ranged from 37 to 67 years and of controls from 42 to 66 years. About 70'/0 of all eligible cases of coronaty heart disease tteated in the three hosp-:rals were included. Resalts The characteristics of the controls &om the thsrc sources wtre compared and no significant differenttis were found. The controls were therefore combined in subsequent analyses. Table I shows that tho cases and controls were similar in marital status, occupation, and educatioa but these were more older subjects among the cases. The mean (SD) age of the cases (58-0 (5•39) years) was greater than that of thc controls (55-0, (5,05) yeass; t-3-69, P-0-002). All the subjects had 1hWed in Xi'aa for more than 20 years. Results on single blind test-retest by two inter viewers on 35 hospital subjects (16 tases and 19 controls) showed good agreement, ranging from 75% to 95°!. for the 10 risk factors tested, with K values raaging fram 0-4 to 0-8 (nine x values with P< 0-01 and one with P<0•05; data not shown). Table II shows that the eaposure to passive smoldn~g in the misdiaguosed controls was similar to that of the controls shown not to have coronary heart disease but 1%, differeat ftom that of the cases. There was no history tdwr~ of excxss exposure in the misdiagnosed groups, suggesting that there was no subjective bias in the ~ interviews. M For passive smoking from husband, the crude odds ratio was 2-12 (1 •06 to 4-25) (table III).'I'b.e sizea of the ~ living qnartess of cases and controls who were exposed .~ to passive smoking from husband were not signh'i- rsntly d"iffereat. Table III also shows that the crude ~ odds ratio for passive smoking at work was 2-45 (1-23 ~ to 4•88). The statistical power, calculated from table W III with a sifpificance level of 5'/0, was 79°/.. Table IV shows the resulta of stratified anatysis for the naro rwestrer.a of passive smoking. The odds ratio for 1 1 BN1J VOLUME 308 5 r-ssxunxy 1994 381

4 a • .1 2,0-JUU-1994 i4=57 a.uuavtu+-~+ .+}+vouac w aiuw av...r..q -. ..., .,.n ..atyuu~ higher than expected from the additive model (2•07+ 2-53-1-3-60) but much less than expected from the alultiplicauve model (2•07x2-53-5-24). The crude odds ratio for any exposure (from husband or at work, or both) was 2-87 (1-28 to 6-55). Table V shows the final model of logistic regression analysis wt3ich included passive smoking from husband and at work as the base (these two variables were included irl the model before other variables were entered and tested) and agey,,~h,~g., history of hypertension, ^,Jpe A pe1ro333~Ity, and +h density hpOpFOCC1n cholesterol concentcation. Other risk factots bad also been tested by forward and backward stepwise pro- cedures but none affected the model sigaificantiy. The interaction term of the two passive smoking risk factors (passive smoking from husband multiplied by passive smoking at work) was also tested but was not sigaifi- cutt. The adjusted odds ratio for passive smoking from husband was 1-24 (0•56 to 2-72) and at work was 1•85 (0-86 to 4-00). Both adjusted odds ratios were smaller than the respective crude odds ratios and became non-sigaificant after the other five risk factors svert included in the final model. When passive smolang was removed from the logistic model the adjusted odds TAetsv-bledde eflorirna repwioe mlalys& af riai)facws Adiuxod odd.,.oo (95Y.®fidmoe ioea..p• Pr&Lte F•ma! mndd (saaon 1 to 7): 1 Aso(yars) 1•13(1N4TO1•22) 0903 2 x~:t~t,oE>,,pe~en 2•47(1•14:as-36) 0-022 3'CypeApasmWW 2•a3 (1•31 ms•s7) o•uos 4 Totat c(ta..a.sos (mrd<) s 1•02 (1-01 w 1-03) 6•aoo6 ~~ 0-%(0-90„0-90 0.00 6 Pa,sivessmolimgsum1*usb.oa 1-xs (c-56 to 2-72) o•so 7 pa,.ivo.mokotatwoet 1•65(o•a6tosroo) o•I2 Ot~er modd (fltaaes I to S emd pasd.e ototsg a t.ot0 1•95(O•90 to 4• 10)t 0-0$7 Otker ntodd (6aoa I to 5 md pfm.e fmoldreS SoLf hutDand o[eit40ei.oDboth) 2•36(1•Ol to5'55)t 0•O!9 'Adionw fee tn. otee:v.d.btcs m.he final modd. tAdleNttd for dse fitK fine v.ii.ble, .bo+e: oEds atlos Ios tLm r.riablet m tho other modds waa es.mdslly me same u dnou Ywevn above and sro aot1eowa. 44 71 495 3101 P.010i013 (1-92)Vbut was sriil not signi5cant However, the adjusted odds ratio for any exposure (from husband or at work, or boih) was 4o ificant (2-36; 1-01 to 5•55). The relation between odds ratios and amount of exposure to passive smoking from husband and at work were examined. For passive smoking from husband, the crude odds ratios showed significant linear trends with amount smoked daily by husband, duration of a(posure, and cumulative exposure (amount daily multiplied by duration), but the aends became non-sigaifinnr after passive smoking at work and the other five risk factors were adjusted for in the 5nal model (data not shown). However, for passive smoking ac work, table VI shows that sigaiScant linear treads were found for the crude odds ratios in amount smoked daily, dusation of exposure, number of smokers, esposure time daily, and cumulative exposure. For adjusted odds ratios, the linear trcnds were significant for all the variables except duration of saposure. When passive smoking from husband was removed from the logistic model, the odds ratios for passive smoking at work were only slightly higher, suggesting that the effeet4 of mtilticolineasity of the two exposure variables were small. Table VII shows simiIar results when these variables were analysed as contiauous variables, and table VIIL shows that there were sigaificant trcnds for the two ir.tdices of combined acpostue from husband and at work. Discussion The outcome or end point of this study is non-fatal incident cam of coronary heart disease. This is similair to those in the previous four case-control studies on passive smoking and coronary heart disease."' 1Host prewous pfospecrive stndies used mortality as the outcome measure. Despite the difference in end poilit, the relative risks for passive smolC3Cg were quite similar.' Although there may be preyalente-incidenee bias in using non-fatal cases, the obvious advantage is that s1le:pauents can provide more and better infor- mation oh expost>re and other confounding factor:. QtlesTionnnirr.a or interviews are the key in3tt(1- ments in studies on passive smolang. Cummings ea al TAata vi--Aauive awbinr ol esnnE and adds raaos ojearvrtarylsma disame Seeeed .d9a.ecd Noof Noof CGndeodd.aeo Faetadjmtatoddaa.tio €•raSue T.aine odds Psaai:em:otm><at.etk eacs ooaaoli (9Y% eonAdmeeuuavai)(95%oonddeaeei6tarsl)' (dobslle><) (I3aouaond) ntivt No ofeiosaes/daf smolred by oo.orkess: o-5(,rnt.urute) 26 e3 6-10 10 23 1•uo 1•28(o-50to3•24) ae7(aao,o2-ss) 0-9s 11-20 13 14 3•42 (1•SS to!•7+) 295 (1b7 to 6•28) 0•019 0•022 3•04 a-2c B 4 6-3e (1-57 re 2ra4) 3-36 (0-B1 m iS-SE) , 3-66 Ten fa amd ntM ". ofazp~(Tezra): 0.S (.aiuaay ssto) 26 t! ~-16 15, P<fl OOi 1•00 6.13 L 12 2•13(0•70tn6•40) 3•OS(0•90rs10•58) 3-20 2-14 25 31 2•57(1•2f1o$d2) 1•56(P61tol-64) 0•24 0•12 1•62 Testfortt,121d XI.7-73, P<0W5 Noot®o)ores 0 26 83 1t+o © s 2 16 36 t•42(o-64co)•1s) 1•16(0•48w2•EZ) r23 3 - - 12 6 6•3a(1L97ee21+51) 5-06(1•42eu12-02) 0•019 0•024 5•17 Z04 S 1 1!•96(1-67to378•20) 4•11(0-39to43-68) 4•SO Nl Trst for ccad ~('-17•50, P<0 00! Fxposnse dme daily (hoas): ~ 0 26 83 1-2 8 30 1 -00 0-8? (0°.1 to 2•23) 0•62 (0•22 co 1-80) 0•65 ~ 3-4 15 11 4+35 (1•164 to 11•73) 4•03 (1•33 to 12-25) 0•001 0-002 4416 O ~05 10 2 i3•96 (2-98 t0113•32) 21•3Y (2-71 to 16a•DO) 22-49 r + Tar Coramd z'-21•58, t<0•0001 ~ Cumulatlre o:vowre (dsaccsa/dayayeari:.mokess+soue,): . 0 26 83 1-00 1-2000 13 32 1•30 (0-35 to 3-03) l•00 (0•)9 te 2-57) 1-05 2001-4000 5 3 2-00 (O•S1 to 7•55) 2•03 (0••17 [o 8•67) 0•00S 0•003 2.11 ~ }I001 13 3 1S•96 (3-B9m 75•27) 9-23 (2-01 m42-23) 9-63 Teat foe ecad )e.ZO•76.P <0•001 Aajt>.d~fr,rye. Lataay et>aspeemom, pasonaury t7p., toaw dsolnmai, biah destritykyoprotein eholeaetoL .nd pa.irvs rmolmes from pwb.nd. }Adiwtod for ..:ia6los.bo+rq exapt for pri+++"c unoJimg &M Ausband. Tht 9'SY. ean8dmcc ocn..b .,,, a11 dis6tlr hi8he utd rbe ! values atc al1 a(i~ lo.er t6m tho.e borStxt ufitvted oddr ratio md are noc.hmea 382 B.titJ yor.uME 308 5PRastuam 1994

20-JUL-1994 14:57 -r,ax e.vn-Paszivc s+wkiar e+ aaorJe as rontinrreus varia~ and odds rudos oJco.onary Tuarr deuars second crude odds ru;4 P'aie,dinued odds r:r;o- ad;,lasd P.as'r.r.o,o)oo¢.cv«kncenanuous.anable. (95Y.eotfldmceMtern!) (95'/.eon!' emtclva[) edd3tuiot Amouni daily (dtueQedoa7) 1•066 (1 -035 to 1•106) Durn;onofezm.u=e (veu+) 1•a17 (1,o1sao 1c76) Na of fmokers 1-633 (1•26S to 2•1DU Esyosura- doly (hau+) 1•480 (1•234 to 1•775) Cmauiadre Qpo+uze (oyutuc+Iday-Y- „aokM:houts/100) i-03a (i020to iOSa) 1-050(U007 to 1•094) 1•D51 1-027 (a-sn3 to 1-061) 3-o2a 1 -425 (1.o4a ro 1 -937) 1-ao 1'1+7 (1•145 to 1•829) i•a5f 1-031(1-0S t to 1•D62) 1-032 -ndj„ta (or age, histaty of hvs«unsiatr Qer,ae,vn M)e. WW d>olccaa, ludt 4Mw 1*0~ aba"wa. aad as,ai.e.moiwot liom -'--^ + tr,a;taeed fu..3;.bLe. .1 ae, e:ce" c>x pn•+ve ,awtons sum hwssad. The 99.4 eontldmn mtMv11S .R .u ,asadyh;d.athn aho.e(or d+. rnY,eimrcd odds twoft .odare ea abc+.a. r,," vm--Q.ntiard ePa+lne w 9anicr srtak* !-« tturr,ond and ot marir aadoddc raaos ejeormroyl,rm dvau Pr.tue Yva7ue Adionad tteds raao (slobs Pmeu Indirnefeembieeidapmvxs (9SYsmefidtncriosnyd)• te<t) Rsod) >>,a~ w 0 t.oo 1-499 1 .79 ("5 so 4•92) 500-999 rs5(o-92to?•io) Da4 o-a23 ? 1000 3•9S (1-03 w 15•33) taees B=: Saoes D (nii) 1.00 se«. i powssyo.ate) 1•~s (o ss w ras) seoee 2(mod=su ayo,etc) 3-l l(1,os m 9•12) 0.059 0.008 scwe 3Nd, croaare) 7-61(1•15 to 50- Is) ',wmmd sK s•, hatar9 ef>>"enrommf pR,oayxy rmw. tow doks- tadL and high des.in fiaowe® mdamrai. tSum ot cuamladve eTomme (mm httsbmd (dprauea/d+r7-mrs) and m mda oe-posur. at r+oet (.mo.m eWo.ed/d.r=d-t>on otCXy-). 3Cumubwe uyonue from Lu,b.ad (dtaasddqinats) .u aecoded iMO Couc otq.,ti~ (foo(e 0-!w erpenat. tooeo 1- 1-099, seott 2-400• 799, aeote 3>soo). .ad cummul,dve esro.tm u woek (ciPsoadd.r= yasssanokas.Lmes) waa recaded into laos etugvoo (surt 0-no cqx.ure, mom 1.1.2oce, .core 2.zoo1-400), scm as4oot). sat mo sooess .ete .dd-3 (r.nse D-4) .od ,ecnded inra 4 oeo=ma (sute o.no c+poaee. rea[t 1.1 w 2, 3eose 2-3 to 6. /CDIt 3-5 eo 6) to &tat Iolks 8. showed that subjects were able to report an accuratc histoty of exposure to passive smoking: the level of agreement between subjects and su:rogates on exposure to tobacco smoke at work was 78°le (x•.0•5); the level of agreement for exposure to spouse smoking was 86% (K-o-7).= We used the test retest method with two interviewcls: the agreement for passive smokiag at work was 74•3'/0 (k-0•5, PG0~01), and for passive smoking from husband the agteement was 91•4% (K-0•8, P<0'01). We did not interview subjects again on quanuty of exposure, but for this aspect the agreement should be lower. Validation by cotinine testing was not possible for past exposures in case-control studies. The analysis for trend should yield better evidence for causal inference of whether or nor there is increased risk due to exposure but would not be precise enough for risk assessment for unit dose of eYposure. Because different sources of subjects might be a potential source of bias in the present study, exposures to passive smoking in each of the two series of cases (those confirmed by coroaary ureriog(aphy and by myocardial infarction) were compared with exposures in each of the three sources of controls (cases confirmed negative on coronary atteriography, outparients, and community controls). The crude odds • ratios for passive smoking from husband ranged from 2-0 to 2-3 for cascs confirmed by coronary artcriography and from 2-0 to 2-2 for thosc confirmed by myoeardial infarction; for passive smoking at cvork, the crude odds :atias ranged from 1•8 to 3-6 and from 1-9 to 3-6 respectively. As the results of separate analysis were consisteilt, pooled analysis was justified. Results of various quality control measures on selected subjects suggested that the data should be reasonably reliable and free from bias. Moreover, people in Xi'an were unaware of The issue of passive smoking, and bias due to overreporting of exposure in coronary heart discasc patients was 3mlilce3y. 'f he bias 44 71 495 3101 P.a11i013 due to misclassification of current and ex-smokers as lifelong non-smokers should be small bocause the prevalence of femalc smokea in China was very low as compared with Western countries. Tiu prevalenoe of rcgular smokess in females aged 40-65 was 8•6% in nce province of Shaanxi, of w3vch Xi'an is she capiral." Both this and our previous studies showed that passive smoking from husband was associated with coronary heart diseass. The crude odds rado of 2-12 (1•06 to 4-25) in the present study was smaller but consistent with the value of 3-00 (1-26 to 7-17) in the previous study.' Although the adjusted odds ratio of 1-24 (0-56 to 2-72) was not statistically significant, it was consistent with the previous adjusted odds ratio of 1•50 (1-28 to 1'77). The variables adjusted were not the same in the two studies, and passive smoking at work was adjusted in the present study but not in the previous one. Thus the results of thesc two studies, together with the evidence from other countries, are strong evidence suggesting that passive smoking from the husband is likely to be a causal factor for coronary heart disease in women in Xi'an who have never smokLd. To the best of our knowledge, this is the first study showing an increased risk of coronary heart disease with increasing exposurc to passive smoking at work (ande and adjusted odds ratios were 2•45 (1-23 to 4-88) and 1-85 (0-86 to 4•00) respectively). With the exception of number of years of exposure, the linear trends for amount exposed daily, number of smokers, number of hours exposed daily, and cumulative expo- sure were all statistically significant. These results strongiy suggest that passive smoking at work is a risk factor for coronary hcart disease, even after passive smoking from husband is taken into account. When passive smoking from husband was not included, the adjusted odds ratios were slightly higher. Comparing the odds ratios for the two sources of environazental tobacco smoke, the crude and adjusted odds ratios for passive smoking at work were slightly greater than,those for passive smoking from husband (although the 95% confidence intervals overlapped). If Lliese were not duc so chance, the higher risk for passive smoking at work may be explained by the fact that exposures to tobacco smoke at work are higher than exposures at home because the dcsuiry of smokers is higher at work, and the length of stay at work for a working woatan is longer than the time she is exposed to her husband's smoking at home. Stratified analysis in the present study suggests that the effects of the two ane additive and that there is no significant iateraction. Because the prevalence of smoking among men is high in China and most men smoke freely at home and at work, women arc heavily exposed to environmental tobacco smoke and the magnitude of the risks could be quite high. To conciude, the present study provides furrher evidence that environmental tobacco smoke, including smoke at work, is likely to be a cause of coronary heart disease. ?he weaknesses of the present study are recognised and further studies are required to investi- ~ gate the role of passive smoking at work and its ~. intcraction with passive smoking at home and from other sources. However, China is the largest producer and consumer of tobacco in rhe world-30% of the l~ world's cigarettes are consumed by China's 300 million }A smokers. In 1984, the prevalence of smoking in the ~ popuiation aged 15 and above was 61% in men and w. 7% in women. Forty per cent of non-smokers were exposetd to environmental tobacco smoke for over 15 ~ minutes a day: 67% of the passive smokers were exposed at tsoase, 14"/o at work or in public places, and 19% both at home and at work." Smoking among young people has increased in recent years." Despite the eGilrtS to control 319a1'.ins, most women ara sti3p BMY voiuaE 308 5 gseRunaY 1994 383

2.0-J1JL-1994 14:58 OiII1C2I impucOti00.s • pphether passive smoking is a cause of coronary heart disease is still tontmveaial • Previous studies have shovrnn that coronary heart disease iu assocazted rvith passive smoking at home but not ©aislt passive smoking at work • This stndy shows that for womea's passive smolrini, at work there were sigui5cant liaear trcnds of iaasased xisks of coronary hcart dlstasa with +^masing eaposures, even afcet adiustmeat for major risk factors and psssive smoidag from hasband • Urgent public hralth measures src nccdcd to leducC smoking m China rxposed to tobacco .naoke at home and at worlr. They are also tu>aware of the Inazards of passive smoking sad are in a disadvantaged position to protect themselves from environmental tobacco smoke. Urgent public health measures an required to reduce smoking in Chiaa so as not only to protect women from eaviron- mentsl tobaceo smoke but also men from the hazards of active smokiag. We t5anic the 3rd Intenational Confa+sce'oa Pterentive CArdiolov for its Young Iavestigswrs Aoard, the Stm Yat Sen Fowxdation Fund, and the Chiaa Medial Board FeIIow- 44 71 495 3101 P.012i013 ship of the Facvlty of Medicine, Univexaily of Hong Kong, for suppoeaag Dr Y He's trsearcls in Hong KoaV~Mr C M Wong for sariarfnl advioe, ltiiiss S F Chung for resesrch asssscsnce; and Miu M Chi for derieai assisnoee. 1 Uaiu9 Swa Fa.ssa+mul I'-kCaM AscKY. R.ob.wy A..tA fw 4 y0"s s..M:tr +.r E•••• --I .dw iu~om ma*ioV.W. DC Us Fa.r®®u A.rc+fesAv-w. 1992, z Mmoc s+L FM+es urm. r,.c,o soimW ,m l.ca,c m~ .o:...iniopr, yayfi0iep,.nairoee®isr. Gl'~ar..~.19s1,aJ:1•1s. s T.ykr A8 J~r DC. Kaa® ii fievfeaoawY wira. ®ots aea nnGo.,.euLrdias.clRad:w 1942X&e9v.7o2. 4 Dc`.m -AJ. JL-Lmz~dnt Iiir4 Heiler BF. tSold DM. tsi.e a®ot1M aeA Ae mtefCe>rtsW..k a..Wti..rydadLAGlY.t- iM I;iflc7lST. 5 VecQ+. Ct. D'As.6xe 1. €z as1 bUi. Topne: O. la..l.e Naii.6 ..d Me ri~k~swn ~}oc=dul icLrcam. io.oa 19933~Ly0S6. a l.e Psd. (3t~6edra J.,Me,u.l4tit sama,mn;y.[arNp ar,~y~ r drt o[ Ln =.eQ a.d u®ae saea:or4acatad d+.erea e. y GW 19Sb;Sio47-1QS- 7 SYsa1aA K. lr.e .molia< -8d ths d.k d Lnat drt..e.,fiNLf i!!2'JL'R 9f-!, a Ks Y. fJ LS.>1r IIi L' 7S,?bcui ]t1. Ta GL V7MSe.'. Mow a.ti.a .nameasrearsi'raW- pw,/P+..Fla l9as:ztas.22. ~ Joint Lsnasuuai Sp^cq d Fnesaaoa af Ctadide1'eWadd lln" .: oePd.a+. 21+t F«~. .. SQodadaadnM o( C}iira! Nama.d.auW_ x-Wd6mt .o. alo.b ra .;kuJoi 1T79yMama. 10 Rttlia 7dP. Selecti.e ooear7 xftCd0VMptif• p+R L AfoaaAmmom traefppaeal wchaie. It.Bdqp 19i7;Me15.24. LI &md9v AI$ DV NP- Si.ir:vl..eiak ...eAw rrY.rh. Vd 1. 71.r r.ber m Ooo< . (aUr4e.oj tadis. lJ'M ImomEiOea A~eaq for ltsand, l9sD. 12 Gtatmiwp RAb t•Leldb Sb wbm4 MC, MABb" 1K. Muwuemm a[ >~aas.res.... op.wl.e aae~e.A w 7Ff~~e.:er I9a9;uk1+'~ 13 Wat XZ, fiaes M Cl- DY, 25..{ lYL G® SZ,15s bC. d..9ria 4 .lat I .lr ,l...aw.r .u.i:V ...aw wWobt. 3.114p *ww' Hw ta06bmL 19f1.0aGhoesia 14 MGebr 1. Nw SIC tbrkoa A. Iam T$ Mqq C.3ootft rosi d:as 3 o.m. a smfer eliat• Zsim C.rrt 19l9•,2:7-L uu.w raJ~>>s+~D