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Environmental Tobacco Smoke Revisited: The reliability of the evidence for risk of lung cancer and cardiovascular disease Robert Nilsson ESEF Working Paper March 1998 The European Science and Environment Forum 4 Church Lane, Barton. Cambridge, CB3 7BI~ Tel." 01223 264643 Fax: 01223 26.t645

ENVIRO,~MENTAL TOBACCO SMOKE REVISITED: TIlE RELIABILITY OF TIlE EVI.DkN( E FOR RISK OF LUNG CANCER AND CARDIOVASCULAR DISEASE Dep:utmunt of Genetic and Cellular Toxicology, Wallenberg Laboratory, Stockholm University, 106 ~1 Sto~.kholm, Sweden Tel: ~: 46~ ?30 5700 Fax: (+468) 73:5 7698 SUMMARY The t,,,rpottcd causal association between exposme to environmental tobacco smoke (ETS) and lung c.mce~ ,~s well as coronary heart disease (CIID) in non-smoking individuals has been oFmajor conc.~,, l to,~cvcr, in most previous evaluations of published evidence, insufficient consideration ',~'a~ t.~k,:t~ ~t" d~e impact of bias and confounding. In the major studies where both diagnostic quality as well as exposure verification had been carefully considered, adenocarcinoma was fotmd to predominate. This is inconsistent with the fact that all established human lung carcinogens, including active smoking, seem preferentially to induce turnouts of the Kreyberg I type. Although it is bi,Aogicall.~ plausible that ETS has a contributory role in the induction of lung cancer in non- smoking indi', iduals, a~,'ailable evidence indicate that a major part of the observed increase in lung cancer risk reported from cpidemiological studies on ETS-cxposed non-smokers can be related to miscla.~sificatton of smoking status, inappropriate selection of controls, as well as to certain coufi,,mding factors related to life-style, and possibly also to hereditary disposition. Important ccmtbmidin~ dietary Factors include inter alia a high intake of saturated Fat, which to a varying exte~,t is ¢,.,t~pled to inadequate intake of anti-carcinogens present in certain foods of plant origin. Dose ~csptm:,c extrapolation - supported by the more solid data-base for aclivc smokers - reflects a possible in,.tcase in lung cancer that appears to he more than one order of magnitude lower than indicat~:d b) the cpidemlological studies used to support regulatory action in the U.S. The epid~'~:~toh~gtcal studies on ETS conducted so far lack the required power of resolulion to confirm incr,:,:..cs ia risk of such low magnitudes. ]'he one-sided preoccupation with ETS as a causative fact~,~ ,f lu;tg cancer in non-smokers may seriously hinder the elucidation of the multifactorial aetiol,~y of such turnouts. Pooli,~g data from 20 published studies on ETS and heart disease, some of which reported higher tisk~ ti,m is [_nown Io be caused by active smo "king, show a statistically significant association with spou:,~l sm,.,king, but not with EIS exposure in the work place. The existence of publication bias for s,,,:ics oa E'I-S and CHD that reported a negative outcome is a matter of some concern. CHD nom:.~ib tricots a considerable proportion of the non-tobacco using population, and a large number of ri~k factors other than tobac,:o smoke have been implicated. Some of these, such as certain dicta, i. lhct,~t~, ~e the same as for the association between ETS and lung cancer. However, in most of t],c ~tudics published on the relation between ETS and CHD even many of the most common conf~,,~ding risk factors were ignored. In view of the apparent deficiencies in the published studies. there .q)pears to be insufficient evidence to support an association between exposure to ETS and CHD. I.urther, it seems highly improbable that exposure to a eoncentrati0n of tobacco smoke at a level of about 1% of that for a smoker, could result in aa excess risk for CHD that, as has been claimed, is some 30-50% of that found in active smokers. There may be valid reasons other than a hypothetical risk for lung cancer and CHD to limit exposure to ETS in places like offices and homes. Although there is insufficient evidence that exposure to ETS induces asthma, such exposuses a~e likely to increase the severity of this disease, and could also induce an increased sensitivity to respiratory infections, e~pecially in children. INTRODUCTION In a widely cited special news report in Science entitled Epidemiolog~ Faces its Limits (Taubes, 1995), the problems associated with epidemiological studies with modestly elevated relative risks (relative risks, or odds ratios below 2) are discussed, i.e. risks of magnitudes similar to those reported for environmental tobacco smoke (ETS). Somewhat pointedl) il ssas stated in relation to such associations, that "man), epidemiologists concede, that their studies are so plagued with biases, uncertainties, and methodological weaknesses that they may be discernln_~ such weak associations." The well-known biostailsti~ah Norman Breslow of the University ~-f-W-~'figt'-~,S~a~tl-e,~riticized epidemiologists who are carried away by the use of various "fancy mathematical techniques", and continued, L.But the question remains: What is the fundamental quality of the data, and to what extent are there biases in the data that cannot be controlled by statistical analysis?". Tim assessments of ETS conducted by U.S.EPA (1992), Tredaniel et al. (1994a), as well as the two recent articles by Wald's group (llackshaw et at., 1997; Law et al., 1997) on the purported associations between ETS and cancer and ischaemic heart disease, highlight this fundamental problem. Although critical view-points were p~esented by Lee (1987, 1992), the Rese~ch Service of the U.S. Congress (CRS, 1995), an European Working Group on ETS and Lung Cancer (EWG, 1996), as well as by this author (Nilsson, 1996, 1997), it is felt that many of the previous reviews have not paid sufficient attention to the various sources of bias and confounding involved. Due to the impact by the articles by tlackshaw et al. (1997) and a'L"-"-w e~" g[-'(~-997ii~l~iai e~p~i's wilt be given to these two reviews. ~ -- To avoid all misunderstanding, this author acknowledges that ETS may have a contributory role in the induction of lung cancer in non-smoking individuals, On the other hand, dose-response exlrapolation for active smokers and other data indicate a possible increase in lung can,~ef ~'t0 b~-~Udl~]oWrf than that indicated e.g. by U.S.EPA (1992) or by llackshaw et at. (1997). As the Aetifi~'¢~iddh'~ of the International Society for Environmental Epidemiology0 GOran Pershagen (1997) of the Karolinska Institute ("C~?n~i_ct_.~f~interest; pone") recently slated with respect to the role of bias in this context: "Indeed such biases may explain all or pa~ of the sometimes observed increase in relative risk of lung cancer in cases exposed Io environmental tobacco smoke (ETS)." Contra~, to what has been claimed, the more thoroughly conducted studies that were carried out since 1990 have provided progressively lower risk estimates for an association between ETS mad lu~..g c___anc_er. In particular, tiffs has recently been demunsuated by IARC's most recent major muhl-centre study (Bofetta et at., 1997) where no association was fotmd. As for the purported induction of eorona~ h-e-a~t~di~~, this author maintains that there is insufficient evidence to support such an association. Pooling of risk estimates from disparate studies - ETS and Cancer - Aggregating studies by means of a "meta analysis" will narrow the confidence interval, and may thereby demonstrate statistical significance for low risk estimates. Upon pooling the ~¢sults from 37 different studies from all over the world, Hackshaw et al. (1997) obtained a "robust" risk estimate of 1.24 for lung cancer associated with ETS. However, "meta-analysis" should only be carried out when the studies are unbiased as a group, and exhibit certain common basic features with respect to design and adequate quality assurance. The majority of the investigations included by tlackshaw et al. (I 997)

/ //are n~t comparable in many crucial respects such as factors causing bias and confounding, and that can be expected to differ greatly among the countries in Asia, Europe, and U.S. where these ,investigations were conducted. In many studies even matching for age was inadequate, and about half did not adjust for major confounders. Against the advice of its ~ri Scidntific Advisory Board that prcscntcd-~-fi-~h-~bjecf'-~"~d~-v~jk, 1993), U.S.EPA (1992) carried out a similar pooling operation, for 1 ! U.S. studies and obtained an overall risk estimate of 1.19 after adjusting for a very low rate of smoker miselassification bias. By using 90% instead of 95*/, confidence intervals, the meta-aualysis attained statistical significance. The r~';.'~ews conduct~'d'~y the IARC shaft (Saracci and RiboIi, 1989; Trddani'-'~'-~ a-T~199-4~'ncluded no formal tests for heterogeneity when morn- analyses or pooling of data were conducted, in spite of the fact that the results vary greatly by geographic region, and the reviewed studies seem to have been accepted rather uncritically with respect to quality. The U.S. Agency ¢xp.~li~ec_~ted_ the type of approach carried out by Wald's group that consists in first obtaining an overall relative" ns~:'~stimate by pooling the results from many studies, and subseqt,ently adjusting this estimate for bias and confounding using certain default values assumed to have u,tiversal validity. U.SEPA (1992) rightfully emphasized the importance of making such adjustmcms with respect to factors that vary by study and type of society for each individual investigation separately, prior to any statistical treatment. Misrepresentation of smoking status in women is obviously to a high degree influenced by cultural factors such as social acceptability. Previous pulmonary disease, occupational factors, and extremely high exposures to air pollutants are ex~,nples of other eonfoanding variables that could be expected to be much more important in China than e.g. in U.S. or in UK. Some of the Chinese studies actually found a significant association between such factors and lung cancer of a magnitude that sometimes was greater than for ETS, and in view of the difficulties in obtaining accurate information on such variables in this cultural setting, the extent of bias introduced by such confounding may have been considerable. Thus, U.S.EPA (1992) concluded with respect to the 9 Chinese studies so far published that "There is too much obscurity and uncertainty attached to the studies in China for adequate data interpretation". Hackshaw et at. (1997~, on the other hand, included these studies in their analysis together w th 4 later published ifivesttg~ ations of questtonab e q~-'~li~y. How--r~#er'~ these investigators failed to include the results from a major collaborative international case-control study supported by IARC including a total of 650 cases and 1542 controls enlisted in 12 ccntres in seven European countries. In this study a non-si~cant increase of lung cancer risks of 1.16 (95% CI 0.93-1.44) for exposure to ETS from th"~ s"-~o~-, F.!~(0".9"~-1.45) for workplace ex spp._s_..me_z, and 1.14 (O.gg-1.47) for combined spousal and workplace exposure were ob~m-'~de (B~i~d~i al., 1997). Although conceptually sound, the U.S.EPA quality ranking system in four tiers according to "utility" before statistical treatment was, unfortunately, less adequate inasmuch this procedure, in the Agcucy's own words, was characterized by "a high degree of subjectivity". In particular, insufficient weight was given to smoking status. For a study to he at all considered as supportive of either a causal relationship, or of a risk estimate, not all variables causing bias and confounding can be expected to have equal importance, but certain basic quality_~riteria lalust, clc~l_~always be met. Cousidc~ing that a low misclassificatio~'ii~~ia'~'~ers tl~ai suffice to obliterate any statistical association, for a study to bc at all considered, it is of paramoant importance that information on smoking status and exposure to ETS be reliable. In many of the aggregated studies various dcfinit'~f the t~ff~m-~k-~-~'," "~k--~-~dk'e~'~" affd ~'~on-smokers" were used, and the efforts to verify smoking status varied from none at all to measurement of eotinine in urine. In some studies non-smokers may actually have had a history of smoking and some investigators classified cx-smokers as non-smokers. Further, in the majority of the investigations conducted on ETS no consideration was taken of confounding by diet, previous lung disease, etc. Thus, common sense would indicate that many of the studies should not have been included for aggregation by the British team. No amount of statistical manipulation can transfe~r ..X. ~.~u~nber .o.f studi¢~ that..ar._e, basicall.y_flaw~Ld with respect to a crucial factor like misclassification of smoking status into one good. X thnes bias is still bias. The apparent "robustness" of the pooled estimate presented by H~-ks'-'fi~w and co- workers (1997) is, therefore, to a large extent a statistical artefact. Only a few of the 37 studies raet basic requirements with respect to adequate design and quality, e.g. the Fontham multi-centre studies, that of Kabat et al. (1995), and to a somewhat lesser ext"fit the c//ml~ined studies of Brownsola ~1992~~)i' ih~'.~'0nly F~ntham and co-workers demonstrated a statistically significant association between E'I-S and lung cancer. Pooling of risk estimates; ETS and ischaemic heart disease This author has identified 20 published studies on the association between ETS and heart disease, out of which 9 where prospective, 9 case control, and 2 cross-sectional. Some investigations on ETS and heart disease reported higher risks associated with exposure to ETS than is known to be associated with active smoking - a most unlikely finding. Pooled data show a statistically significant association with spousal smoking, but not with ETS exposure in the work place. However, the defects characterizing the studies concerned with passive smoking and hcaiq disease arc even more apparent than for those for cancer risks, especially with respect to the lack verification of diagnosis and exposure as well as lack of control of confounding. In addition, there seems to have been Some publication bias with respect to studies showing no significant assuciatiun (~ee below)_ By aggregating 19 published studies, and not including the large _.Am~[!.cao C .a~._c.e~ Soci_.__e~_CP_~S-I study, Law and co-workers (1997) obtained an estimated overall relative risk in life-long non- smokers who live with a smoker of !.30 (CI, 1.22-1.38), and that is claimcd to be approximately equivalent to the risk associated with s..m.o.~ing..-_oh.t~.~!~_~._e.per day. In its document supporting proposed legislative action on ETS in U.S., OSHA (1994) presented a simila~ assessment. Similarly to what was the ease for the association between ETS and lung cancer, Law ctal. (1997) as well as OSHA (1994) refrained from any quality considerations when selecting studies to be aggregated in a recta analysis, Considering the relatively low risks reported for ETS in the literature, the impact on the reliability of these estimates caused by an extensive lack of control for common confounding risk factors can readily be appreciated. The main reasons given by La~v et at. (1997) for not including the largc._A.~.S_._C~P~-l.study that showed no increase in relative risk were (i) that the results were first presented by "consultants to the tobacco industry" and {it) "the difference is too great for the two_.gro__up_s~of_s.~d._i_e~s-~o-fie__C~.m .bin-~d" as.s~c'~lid estimates; one must be flawcd-'~. ' X~'t~h'c second argument, these authors had ~vldently no reservations against including studies (Garland ct at., 1985; Hc et at., 1989, 1994; Hole et al., 1989 - highest exposure group) where the risk estimates were equally disparate, but in this ease very much higher than their overall.¢ztifaam.oJ" 1.30. As was already mentioned they were even much highe.Lth~n-th~'s~s~o~iated w'~th active smoking. Out of 20 published studies, five are not available as peer-reviewed articles but raerely as abstracts, five are quite small studies (n<100), and in one (Dobson et al., 1991), with 343 cases the results must be considered invalid because data were collected from cases and cuntrols in different ways. As to the latter study, an increased risk was seen in non-smoking women exposed to ETS at home, but not for similarly exposed non-smoking men. There wa~ ..np_o~;k. increase associated with ex_po_su__.r_e.t_o_g.'l~.at thC.w_gr~k" place. Further, no definitions arc given of either "ex-smokers" or "non- smokers". For the deceased cases, the authors simply assumed that the smoking patterns were the same as for non-fatal cases, a source of bias that the authors themselves acknowledge, and they also

/, not~: 1hat "the distributions of so¢io-economic status mca.~ured by education were significantly diflcr,~nt among cases and controls". Out or" the five studies with more than 400 cases (Hirayama, 1981, 1984; Sandier et at., 1989; Layazd, 1995; Tunstall-Pedoe, 1995; LeVois and Layard, 1995; Steenland et al., 1996), the studies by liirayama (1981) and Sandier etal. 0989) are characterized by a number of &feels that makes annb sis less meaningful. Thus, in both studies follow-up was limited to individuals who remained in the study area, resulting in losses from the studied population. Further, Hirayama (1981) defied the ltdes of epidemiology by age adjusting relative risks for the female cases, not by the age of the won~an, but by the age of their husbands. Adjustment for common confounding facturs was not carri,-d out. In his first report Hirayama found no increase in ischaemic beart disease in non- smoking women married to smoking husbands (standardized RR=I in non-exposed; RR=0.97 for "moderately" exposed; RR=1.03 for highly exposed). The time period covered was 14 years. After only two more years of follow-up of the same cohort - and after the first reports on a hypothetical asso,.'iation between exposure to ETS and heart disease were published - this author (Hirayama, 1984) suddenly finds an association, and presents a relative risks of 1.10 and !.31 with respect to ischacmic hea~ disease for these exposed sub-cohorts. When it was subsequently pointed out (Lee, 19891, that such a risk increase during only two years was implausible, the previous figures for the first 14 years were re-stated by Hirayama (1990) to give the relative risks of 1.05 and 1.21. The cohor~ study by Sandier et a[. (1989) represenls a follow-up of two curlier reports on the association between ETS and lung cancer (1985a, 1985b) that do not fulfil minimum requirements for au adequately reported cpidemiological study. For this reason they were excluded in the analysis made by NRC (1986), U.S.EPA (1992), as well as by others. Non-smoking women exposed to ETS had ,u~ increased relative risk with respect to cancers of the cervix, breast, and endocrine glands, i.e. sites ~thich havc not generally been associatcd with smoking. As to the follow-up study, there was a gcnctal increase of all causes of dcarh in ETS exposed. Exposure information was only collected at the imfiatinn of the study, and there was no vcrification of smoking status, diagnosis was based on death certificates, and there was no control of important confounding factors. The authors thent~,:lvcs seem to have been acutely aware of many of these shortcomings, and point out with respect to thclr results that "Misclassification of smoking status is also possible." As to the general incr¢,~c in all causes of death in ETS exposed it was noted: "The general increase in mortality leavc~ open the possibility that the life styles of people who live with smokers differ from those who do not live with smokcrs. Factors such as alcohol consumption or dietary habits which arc correlated with both smoking and risk for some diseases (and which were not collected in the 1963 census) seem especially likely to be alternative explanations for our findings, to the extent that diets or alcohol use are similar among household members." Whereas the smaller studies tended to give higher rdative risks, the reported estimates were close to unity in the more recent extensive studies in U.S. with more than 18,000 cases (Laya~d 1995; LeVois and Layard, 1995; Steenland etal., 1996). On the other hand, the cross-sectional study (n--428) from Scotland by Tunstall-Pedo¢ etal. (1995) demonstrated an association, but there are certain problems w~th exposure characterisation that make the results difficult to interpret (see below). In the CPS-II study, a significaqdy elevated adjusted relative risk was found for men (1.22; C! 1.07-1.40) but not for women (I. 10; CI 0.96-1.27) when based on emrent exposures. Adjuslment was made for a number of confounders, but not surprisingly not for die?~'y factors. Neither the Surgeon General (1986), nor NRC (1996) were able to determine that ETS is associated with heart disease, and emphasized the need for additional studies. The evidence in support of such an association was evidently also found inadequate by U.S.EPA 0992) which refiained from including any assessment thereof in its extoasive evaluation of the effects of ETS. Later studies have given even less reason to change this conclusion. Funding and Publication Bias - In the special news report in Science (Taubes, 1995) that was mcntioncd initially, one researcher with thc National Institute of Environmental Health Sciences, Research Triangle Pa~k, NC, was quoted to say that "Investigators w~ e__~__[~C_t su~_.p_~~ and investigators who don't find_.an_e_ff._ect..~do_n't.j[e_t su_._p__po_.~. When t~mes are tough it becomes extremely difficult for investigators to be objective". Similar problems seem to exist also for the publication of negative result.% especially if the topic is tobacco related diseases. Sweden has the highest number of snuff dippers in the western world (more than 10% of the male population), but the incidence of oral cancer remains~lo~ by internatioh~/[ar-ds. Without being able to provide acceplable e~at]~s, i-~ b~en virtually impossible to have some American medical journals publish the results from two extensive epidemiological surveys recently conducted by Swedish physicians that show no association between snuff dipp.inlL~and._the__ja¢id_gd~c.e_~ur~_ _of._~e head and neck re.gi_~on (Schildt et at., 1998; Lewm et at., 1998). Upon reviewing these studies, ~e'S'-~t~ Government Agency for Health and Welfure judged these investigations to be of high quality and noted, that "although these studies carrot exclude such a relationship, no significant association between snuff dipping and cancer in humans can be established". In a systematic survey on publication bias by Easterbrook etal. (1991), the authors conclude: "we have confirmed the presence of a systematic selection bias in the publication process according to study results. Studies with a statistically significant result for the main outcome of interest were more likely to be submitted for publication and more likely to be published than studies with null results, after adjustment for confounding factors." Where there seems to have been no significant publication bias with respect to the lung cancer studies, such bias seems to have existed for the studies onETS and CHD. Thus, the results from the largo American Cancer Society CPS-I study covering some 15,000 heart disease deaths were never published, but are only "known from indirect sources (Le Vois and Layard, 1995; Law etal., 1997). Similarly, a 2-year study on the atherogenic i~ro__..perties of tobacco smoke in 220 beagle dogs fed 5% cholesterol diet, and that was sponsored and directed by the National Cancer Institute (NClT~c-~-thh"Nali0h:~ff'deart, Lung, and Blood Institute (NHLBI) carried out by Hazleton 1978-1980 seems to have met a similar fate (Hazletun, 1981). Biological plausibility - Lung Cancer - ETS contains the same carcinogens as mainstream tobacco smoke (U.S.EPA, 1992), and it is therefore biologically plausible that ETS could contribute to an increased risk for lung cancer in exposed non-smoking humans. The main problem is to quantitatively define the level of risk, where the quality of the epidemiological information is of paramount Hackshaw et al. (1997) imply that ETS has been associated with an increase in squamous cell and small cell carcinomas (Kreyberg I type) as well as with adenocarcinomas (Kreyberg II) in a manner consistent with the effec~ of tobacco smoke. However, for an analysis of histological type to be at all meaningful, two factors tuusl be carefully considered: (i) diagnostic quality as well as (ii) exposure verification. Most pathologists recognize that a large proportion of the information found in hospital records with respect to histopathological and cytological analysis is incorrect. For this reason Fontham's group (1991,1994) employed a pathologist specialized in pulmonary pathology who found that 20% of the lung cancers were originally misclassified according to histological type.

Secondly, ~iace active smoking primarily induces type greyberg I tumours, the exclusion of active smokers ol cx-smokers who have been misclassified as never smokers is crucial. The Wald group makes the nfistake of lumping all available studies together in spite of the fact that the aforemenlioned precautions had been taken in a fe~v investigations only. Not surprisingly, they In the fi*st ,¢port from Fontham el al. (1991), where both diagnostic quality as well as exposure verification had been carefully considered, an apparent increase in risk was only seen for adenocarci,,Jma,, but not for squamous cell, 6i imhll cdll edr--Cinom~-]ff the fullow-up study (Fonh-fham ct aL 1994), at/ increase was also reported for primary carcinomas other than adcnocarcim,ma, but the odds ratio was statistically not significant. The fraction of adenocarciu-mas was almost 80%, with 20% belonging to other categories. Brownson et al. (1992) as well a.s Kabat et al. (1995), who conducted adequate histological verification for most cases, similarly fi,tmd that adenocarcinoma was by far the most predominant cell type. In the Doll et at. (1957) study on active smokers the relation is reversed; in women only 20% were adenocarcinomas and $0% ~*cre of other histological cell types. The predominance of Kreyberg I type turnouts in some studies most probably reflect the inclusion of active smokers among cases. Most auth,~¢z do not seem to have realized the implications of this finding in a broader perspective. All estabhA,cd human hmg carcinogens, including inorganic arsenic (Newman et at., 1976; Axelson et al., 197S~. asbestos (Auerbach et al., 1984), chloromethyl methyl ether?ois-¢hloromethyl ether (lAP.C, 1'~74), coke-oven emissions (Kawal et at., 1967; Blot et al. 1983), chromium compound~ tBaetjer, 1950; Bidstrup, 1967; Hueper 1966), certain nickel compounds (Sandemaan, 1973; Stmdc,,nan ctal., 1989), mustard gas (Yamada, 1963), alpha particles from radon daughters (Archer et al., 1973; Horacek et at., 1977; Saccomanno et al., 1971), as well as mainstream tobacco smoke, seem preferentially to induce tumours of the Kreyberg 1 type. It is, therefore, biologically lfighly implausible, that in contrast to all other kn'-~'hu"~'rn tSu--I/i~o'nary carcinogens - including active smoki~g - ETS should induce mainly adenocarcinomas. The objection could be raised, that mformauon oa the agen s described above~ve almost exclusively been derived from exposed male workers. Thns, in female active smokers the associated incidence of adenncarclnoma tends to be higher than for males, but there is, nevertheless, a marked predominance of Kreyberg 1 type turnouts. Hackshaw ~t al. (1997) quote evidence that ETS exposed individuals exhibit increased levels of DNA and haemoglobin a,lducts characterized as "tobacco specific adducts", and conclude that "It is therefore exl.cctcd that exposure to enviroument'--aJ t'ob"~£d sr~'~ c~ses cancer". Firstly, in all of the four cited studies, d-aminobiphenyl (4-ABP) and 3-aminobiphenyl (3-ABP) adducts in haemoglobin were measured, but no DNA-adducts. Further, 4-aminobiphenyl, an antioxidant in robber, is ccmdnly not specific for tobacco smoke, and 4-nitrobipbenyl - emitted by e.g. gas stoves - gives the ~unc addnct. Secondly, the measured increases in adduct concentrations were small, highly variable, and for many exposed individuals not even detectable. When, e.g. in the study of Maelute et al., (1969), purported n_on-smoking E'l'.S._~posed individuals who had adduct levels consistent xsith active smokin.g (g5-1-50"~pg/g haemoglobin) ~e ~J~cquded, the response in ETS exposed indix iduals becomes even less convincing. Thirdly, the presence of an adduct like a,_~p in haemoglobin can at mos! be used as a measure of exposure, but not equated with a pro-mutage~c (cancer initiating) lesion in DNA. ~.~q~ereas in a large co-operative study sponsored by U.S.EPA, a significant increase in pm- mtltagenic DNA adducls as well as DNA damage in lymphocytes could be linked to exposure to ambient air pollutants, neither DNA-adducts (assayed by the super sensitive 32~ postlabelling assay) nor DNA damage was found to be associated with exposure to ETS (Binkova et al., 1996). In contrast to ETS exposure, a striking increase in promutagenic adduct levels from the potent carcinogen benzo[a]pyrene could, on the other hand, be detected upon consumption of grilled hamburgers (van Maanen ct al., 1994). This polyaromatie compound h~ a carcinogenic potency equal to that of NNK, the most active among tobacco specific nia-osaralncs. In conclusion, the predominance of adenocarcinomas that has been found to be associated with E'IS in non-smoking won~~i~a ~ ]~rgerstu~lics ~i"~dd~-~tc quality, is inconsistent with the induction of hing cancer by tobacco smoke as well as by other known pulmonary carcinogens. For this reason, a significant part of the increase in lung turnouts seen in individuals exposed to ETS is most pr_oba_.__bly..ea_..us_e~l_ b~y. other facto_~o The Aetiology of Adenocarcinoma in Non-smoking Women - The incidence of lung cancer in non-smoking Chinese women is extraordinarily high, some 2-3 times higher than for U.S. non- smoking women (IARC. 1990), a fact that cannot be ac¢oumed for by exposure to tobacco smoke (Gao et al., 1987). Except for some geographical localities, e.g. Xuan Wet, Yunaan, this can also not be explained by exposure to other air pollutants, like the burning of smoky coal. The remarkable fact is that these high incidences - as well as the marked differences found between different ethnic groups of Chinese - are retained in the Chinese female populations in Singapore (Law et at., 1976; Coleman et al., 1993), l,long Kong (1-1ong Kung Cancer Registry, 1982; Coleman et at., 1993), as well as in U.S. (Fraumeni and Mason, 1974; tlinds et al., 1981; Green and Brophy, 1982). The fact that adenocarcinoma in non-smoking women is much more prevalent than in non-smoking males, as well as the large differences for lung cancer prevalence in non-smoking women between different ethnic groups, has been attri..ku_.~.to hormonal factors by some authors (Chaudhuri et at., 1982; Lubin and Blot, 1984; Gao et at., 1987), but dietary and/or heredit _~," fa__.cturs may also be invo_~d. Biological plausibilily; Coronary Henri Disease - The improbably high risk estimates (Law et at., 1997) obtained by pooling data from all available studies on the relation between coronary heart disease (CHD) and exposure to ETS point to the presence of considerable bias and confounding. The increase in mortality risk with respect to heart disease is relatively modest for active smokers. Thus, Pfaffenberger et at. (1986) give an estimate for relative risk of 1.84 (CI, 1.64-2.04), whereas in the British Doctors study the reported risk was 1.56 (Doll et al., 1994). A somewhat higher risk of 1.94 (CI 1.80-2.08) was reported by the ACS PS-ll Study (Steenland et al., 1996). For this reason, relative risks associated with ETS in the range 2-14.9 as reported by tie et at. (1989, 1994) from China, by Garland and co-workers in the U.S. (1985, 1986), as well as by Hole et at. (1989) for the highest exposure group, lack all credibility. These studies were all included m the meta analysis by Law et at. (1997). The cohort study published by Garland et al. (1985), where no definitions were given of "formeC or "never" smokers, give an adjusted RR=I4.9 in non-smoking women married to current or former cigarette smokers. Not only ¢,'ill lhe low number of eases (n~19) in this study prevent a meaningful analysis but, in addition, it seems that the authors got their data mixed up, and subsequently, the sensational ILK of 14.9 was reduced to RR~2.7 (.Garland, 1986). Using the estimate given by the Wold group (Hackshaw et al, 1997) themselves, that exposure to ETS corresponds to 1% of that for an active smoker, simple dose-response considerations would indicale that their own estimate of RR=1.30 is wholly improbable. Rather than choosing the most simple and likely explanation for this "large effect from a small exposure" (Law et al., 1997), namely that the risk estimate obtained is biased, a number of more or less credible hypotheses have been advanced. "~'-~

In the co~Icxt of a possible association between ETS and heart disease, a possible role of carbon monoxide due to the formation of carboxyhaemoglobin (COHb) has been considered (OSHA, 1994; Glanz and Parmley, 1995). However, in the case of ETS the Icvcls of COHb are only in the range of 2.-4%, lying just above natural background levels that obviously arc due to bacterial formation of CO in the intestinal tract. Based mainly on some heavily criticized investigations (NRC, 1996) of very limited size, Glanz and Parmley (1995) as well as OSHA (1994) claimcd that COHb at conccntx.qions in this range, and down to 2% r~.y_~ggravatc angina, a level not uncommon in individuals exposed to exhausts from automob~cr cities, liowcvcr, a more thorough study with the p~ticipatiun of U.S.EPA coul~cmonsu'atc any clinic.ally, s_i n?L~.C~._~h.I effect even at 3.8_°/.~_~ ~:Olib either with respect to the onset 0f angina, or on other relevant parameters (Sheps et al., 1997). In addition to effects on plasma fibrinogen concentration and high density lipoprotein cholesterol, Law et al. (1997) correctly assess the possible effects of ETS mediated by COHb as being of minor importance, and focus their attention on the effects of tobacco smoke on platelet aggregation. Although it is clear, that platelet aggregation is affected by active smoking, adequate evidence demonstraling that this effect "may account for the large effect on risk of ischaemic heart disease" from tobacco at the extreme dilution represented by ETS is lacking. To support this postulate, Law et al. (1~97) cite one flawed human study, as well as experimental evidence. In the experimental study on I':TS by Davis et al., (1989), the effect on platelet aggregation and endothelial cell counts were re,;otded a~er 20 minutes' exposure of 10 young males to tobacco smoke ia a hospital corridor, lhe values observed a~er exposure to ETS were compared to those found after 20 minutes' "control p~riod" which "consisted of siRing in the laborato~, where smoki!)g.~ prohibited". Given no description of the laboratory in question and its use, t--he ti--~me spen-'-'~t-i~ the ho-~pi-~l--~r~aor might as well have been the real "control period". Exposure to ETS was monitored by measuring carboxyhaemoglobin as well as plasma nicotine. Small changes (exaggerated in the published figures b:," magnificatiun era section of the vertical scale) were observed for these factors. However, "After passive smoking, the percent carboxyhaemoglobin level did not correlate significantly ~.P>0.60) with the piatelet aggregate ratio or the endothelial cell count."...'bleither the plasma nicotine concentration after passive smoking nor its change from before to after passive smoking was significantly (P>0.20) con, elated with the corresponding values of the platelet aggregate ratio or the endothelial cell count". The authors finally point out that "The significance of enhanced platelet aggregate formation and an increased concentration of anuclear carcasses of endothelial cells in blood after passive smoking is not known." Obviously, no valid conclusions with respect to the effects of ETS on platelet aggregation can be drawn from this study, nor from any of the other cited investigations, In view of the relatively low exposures used, Glantz and Parmley (t995) as well as Law et at, (1997) put considerable emphasis on the results from the experimental investigations on the cardiovascular effects in rabbits and rats induced by ETS published by Zhu et al. (1993, 1994). However, these studies exhibit some unusual and most puzzling characteristics that indicate that they did not conform to GLP standards, including a lack of adequate control of exposure, as is e.g. shown by the finding that there was a statistically significant increase in the COHb concenlration also in supposedly "non-exposed" control rats (Zhu et at., 1994). Further, as judged by COltb levels up to 9%, the exposures used were far above those representative of ETS. Whereas there was a gradual increase in total cholesterol in controls, exposure to SS was found to cause a gradual decrease. Finally, the experimental protocol for the rat stodies reveals a number of artificial features, e.g. artery occlusion by a coronary artery snare occhider - that resulted in an approximately 35% infarct size area was found already in the controls - that makes comparison with exposure to ETS in humans extremely diffic,tlt. Similar objections can also be raised with respect to the promotion of l0 the spontaneous development of aortic plaques in birds by SS (Penn et al., 1994), especially in absence of adequate control with respect to the effects of stress. In the rabbit study (Zhu et al_, 1993), the area of atherosclerotlc changes was said to have been significantly higher in the aorta and the pulmonary artery in animals exposed to artificially produced ETS, than in controls. Atherosclerosis, although very difficult to produce in experimental animals like rats, can be induced in the rabbit under certain conditions. However, even in this species its development is slow. Thus, it is highly surprising to find that about 3~/~ of the surface area of the aorta, and about 25% of the pulmonary artery was covered with atherosclerotic lesions already in young controls after !0 weeks, and it seems likely that these rabbits were highly atherosclerotic already before the initiation of the study. In view of the their slow development, these changes were either due to disease or some hereditary defect, and a certain modulation of the extremely high background level observed can, therefore, have another aetiology than exposure to ETS. The predictive value of animal models such as these could at any rate to be very limited. In the large NCI/IqHLBI 2-year study mentioned above, increasing levels of cigarette smoke, CO, and nicotine during 2 years significantly reduced the severity of atherosclerotic l~siuns in 220 beagles while fed 5% cholesterol (Hazleton, 1981). Bias and confounding - Lung Cancer - Some investigators have suggested that most (Nilsson, 1996, 1997; Pershagen, 1997), and possibly all of the observed increase in cancer risk (Lee, 1987, 1992, 1995; Lee and Forey, 199:/, 1996) associated svith ETS can be ascribed to bias and confounding. Whereas OSHA (1994) failed to make any attempt to assess this problem in an adequate manner, U.S.EPA (1992), Wald's' group (llackshax~ et al., 1997) and others have been aware of the important role of such factors, and have in various ways attempted to make appropriate adjustments. Because smokers tend to live with smokers (Lee, 1987; Lee and Forey, 1996), the tendency to have the same smoking habits (expressed by the concordance ratio or aggregation factor) was also taken into consideration. However, they have underestimated the extent of smoker- misclassification bias, as well as the limited impact when correcting for confounding with respect to measured variables that are inaccurate descriptors of the underlying cause. Despite the critical viewpoints presented above, the relatively well conducted investigations by e.g. Fontham ct ale (1991,1994) do indicate an excess risk of lung cancer for ETS exposed non-smoking women similar to that indicated by Hackshaw and co-workers (1997), although this risk is characterized by a much broader confidence interval than that derived by aggregation of studies. The question then remains to what extent systematic bias and confounding could have been involved, and the Wald group made some efforts to estimate two systematic sources of error: misclassificatiun of smoking status and diet, while others were ignored, although the latter were probably important in some of the studies, particularly in those from Asia. Further, it seems quite remarkable that this group does not even mention the difficult issue of recall bias that is bound to have a major impact for studies with a large fraction of surrogate responders. Misclassifieatiun of smoker status • Due to the fact that most lung cancer cases can be attribotcd to active smoking, the ,¢,~.~f_ sver smp.ke~rs from repo~te_d___n__cv~cr smokers is of cardinal importance in this context. The critic~" ~drt from ~ "c~"~ns of ~he ~-C~n~'~olicy Research Division of the Research Service appointed by the U.S. Congress (CRS, 1995) noted e.g. for the Fontham ctal. data, that smoker misclassification rates less than 10 ]~_r cent would account for all of the measured risk at the highest exposure levels in'g~osc studies, "~n"~ even smaller rate - less than 3% - would cause those risk values to be no longer statistically sign/ficant at the 95% level For this reason, and in order to obtain objective verification of smoking status, in somc studies active smoking was ascertained by measuring the metabolite of nicotine, cotinine, in urine or saliva. II

U.S I~PA (19~2) divided misclassified smokers into the categories regular, occasional and ex- smokers, and passive smoking relative risks were corrected using a method proposed by Wells and Stex~'a~. AIthm~gh objective verification of smoker shams is problematic for occasional smokers, Hackshaw et al. (1997) makes no provision for this group that presumably was included among actixe smokers. Based on a selection of data from studies inx'olving e, ane.er cases, an overall misclassificatio~ rate of 1% for current regular smokers, 24% for current occasional smokers and 12% for ex-s~lol:ers, respectively, was obhained by U.S.EPA. On basis of a selection of 6 inve~ligation.s from Europe and U.S., Hackshaw et at. (1997) used an average misclassification rate of 2.t~% (range 0-3.3%) of the reported non-smokers that are actually active smokers. Using a much larger set of 42 s~udies, Lee and Forey (1996) found that the range of self-reported non-smokers who~c cotinine valnes indicated current smoking varied in various s~udies from a low of 0.5% to a high o~" 17.4%. Thns, not only was the selection of misclassification data by U.S.EPA as well as by the/~,,~ld team bia.ged, but the latter also make the unwarranted assumption, that misclassifications rate~ t~om U.S. anti UK studies would also be applicable to populations in countries like Greece, China, "and Jap:m. Although the data of Riboli et at. (1995) indicated small differences in misclassitlcation rates between participating cen~res in U.S., Europe and Asia, it is unclear on what basis the subjects had been chosen; there may have been extensive selection bias, and the representativity o~" li~e population samples may also be questioned. Lee (1995) published results that give an~ple support for an extremely high misclassification rate in ./apanese woman that will make any conclusions cow,reining Ihe association between ETS and lung cancer in non-smoking Japanese women extremely l~recarious, if not invalid. Using cotinine determination in saliva, Wewers et at. (1995) compared self:reported smoking with results from 783 immigrant men and 620 women from Cambodia, Laos, ,~r,,l Vietnam residing in Ohio. 58% of aIl~e_ver smoking women who were current smokers reporled being non-smokers, and 11% of the reported non-smoking women were found to be eurrem smokers. Undoubtedly, similar situations exist in other "traditional societies~ like China, and to a lesser extent also in Greece for women in the age group of interest here. Citing a~ overall r~te of 5.7% smokers misrepresenting themselves as non-smokers in four non-lung cancer cuhons from I IK and LLS., L1.S.EPA (1992) holed, that reported average misclaasification rates for lung ca~cer cases tend to be mu~h lower, and rejected the former estimates as unrealistic and not applicable t3~r adjustment of estimated risks associated with ETS. The situation may be just the opposite, and brings into focus possible life-style changes - including dietary and smoking habits - induced b2,' ~he detection of disease, and that may introduce a substantial differential bias. A change of dietary habits can be expected to limit the usefulness of food intake questionnaires in probing the pasl dics:~ry habits of cancer patients and, in addition, many patients will no doubt also give up smoking. The: impact on tendencies to misrepresent smoking stares is likely to be complex. Before discovery ~f ~l~e disease the would-be cases will, obviously, be as prone as the rest of the general popalatlo~ ~o misreport stun "king status, and in many cases diagnosis of disease will not restore a person's ,'r~thfialness, especially if he (she) is residing in a country where one may have to consider previous s~tem~en~ made with respect to insurance po!ic.i~___.vcifll diffe~ntiat~...p_~mi_~ (CRS, 1995). Ach~all.',', there i-~iiilTni~-t~t"a~'-m-~r~:]~ii.;se~Latio~'-of smoker shatus is higher among patients who have been._....a~d~!s._e_d..~?_.quit__s~ng than among individuals from the general population (Veliccr et al., 1992). The high proporlion of cancer cases that were unable or unwilling to provide urine san~ples for cotinine determination in the reports from the Fontham group (Ir991, 1994) as well as in some other studies fans a suspicion, that some of these patients for various reasons ,~e~ active smoke___~ but~wan_t_ed to collgf~.~is_.~ct._._~boli et at. (1990, 1995) and some other studies that cite low misclassifications rates similar to those of the Fontham group (1-2%) provide no inform~tion on the percentage of individuals who refused to provide urine samples. Fontham et al. (199.1) acknowledged these problems, but failed to modify their estimates of misclassificatlon rates accordingly. According In the opinion of this author, it would appcau more appropriate to use the misclassificcaion rates for "healthy" controls from the general population rather than the "apparent" values from cases when adjusting relative risks, or odds ratios. If the 5.7% overall rate oiled by U.S.EPA (1992) for the general population is employed, the association "bet~,,-~en]-2TS /u/d-Ifai~ i:~gnY.i:r ~ll'~61"~flaih statistical significance for the published studies from By relying on the use of cotinine as biomarker not only vdll some active smokers go ~ because of inter-individual differences in rates of metabolic conver~~e (see below), but due to it~_short half-life (18-20 hr)~ a tung cancer case chssified as non-smoker based on cofinine determinati~m~, ih--~'ri/~i'l~'l~, ligv~~'~n ~i a~ff~e S~n~0kdr'alt hd li-fg h-ntii a--'~ouple of days before sampling took place. While not admitting to have recently been an active smoker, some cases will stop smoking after detection of the disease, a change of habit that will ~go undetected and resulting in the inclusion of an "ex-smoker" with a cancer risk of th~,if~r an active smoker. In view of the fact that there is n_gbiom_ar_l~r that can be used objectively to distinguish ex-_~rs from~e~ve~'~o~k_ers, the misclassification rote for this group is highly conjectural. The method used both by U.S.EPA and by Hackshaw et at. (1997) consists in making comparisons of self-reported smoking for one and the same cohort at two different occasions. B~ed on one single (sic!) study (BriRen, 1988), the British group estimates that ..~ of ever smokers were former smokers misrepresenting themselves as never~.k.~.rs. NRC (1986) cites (p. 235) one study where 4.9% of the subjects said that they had never smoked as ranch as one cigarette a day in 1982, when in fact they had previously smoked and reporu:d so in interviews, la the extensive study from UK reporled by Lee (1987), and that included 1537 subjects, 10% who in 1985 claimed to be never-smokers had five years earlier admired being active smokers, or ex-smokers. Even higher frequencies (I 7%) of inconsistent reporting were found in the WHO MONICA (Multinational Monitoring of Determinants and Trends in Cardiovascutar Disease) study in Germany (Wynder, 1993). Lee and Furey (1995, 1996) could confirm very high rates of ever smokers that later claimed never to have smoked; 11-18% in men and 5-/% in women. According to a report by Auerbach et al. (1984), upon re-interview of women who were listed as non-smokers in hospital records, 40% admitted that they had actually smoked. As demonsL~ated by Heller et al. (1993) who determined ¢otinine, not unexpectedly, many persons who previously gave false information on smoking habits will do so also at a later occasion. Citing themselves, Hackshaw and co-workers (1997) consider that their estimated misclassification rates are "likely to be robust'. Referring to incomplete evidence published by Lee ~1987) and Wald et at. (1986), U.S.EPA (1992) assumed that the majority of all misclassified ex-smokers gave up smoking at least 10 years ago carrying an approximatelL_13~.~ fis'~m relation to that computed for current smokers. The sole documentary basis given by Hacks~w et ~l. (1997) for endorsing a similar conjecture is a personal communication from a certain N. B.r.~n. Since cotinine data cannot'i'-d~i~guish an active smoker that stopped 2-3 ~-~o-/'r~'m'-~TrU~'~on-smoker, the risk for ex-smokers that misrepresent themselves as never smokers could, in principle, be equivalent to a weighted average from twice the background risk (very long time abstainers) all the way up to the same risk as for a current smoker. Bias due to Exposure to ETS Outside Home and Lung Cancer - Exposure to ETS outside home undoubtedly does occur to an appreciable extent, but Phillips et al. (1994) estimated this source to be less tmportant than exposure at home, a conclusion that was supported by the large international study by R~|~ et al. (1990) as well as by other investigators (Moms, 1995). U.S.EPA (1992) claims, on the other hand (p. 6-21), that "Background ETS exposure accounts for 2,200 [cases]

(72%) and sp, msal .~moking for 860 (28%) of the total [risk] due to ETS". Further, the Agency asserts that in most epidemiological investigations a significant downward bias is introduced by LMderestimation of exposure to ETS outside home, e.g. at the working place and during travel that compeusates for upward bias due to misclassification of smokers as non-smokers. Due to the extreme dilution of ETS in comparison with main stream smoke from cigarettes, it is hard to imagine that such exposmgs can noticeably counterbalance significant misclassification of active ~mokers as uon-smok¢~s (CRS, 1995). Also, it seems highly remarkable, that out of some 20 studies, only 2 (Kabul and Wynder, 1984; Fontham el al., 1994) have provided• any indication at all of an associat~~fin~'cancer and exposure outside home, an outcome fl.0%) dual could be attributed to chance. The first study by Kabat and Wynder 0984) includes very few cases, and a small, but statist/rally non-significant positive association between exposure at the workplace and lung cancer in non-smnkers was found for males, but not. for females. In their subsequent, larger and more c.a-¢thlly designed study there was no indication of such "an association (Kabat ct at., 1996). In the Fo,th.un ¢t al. study (994), a stgmficantl), mci'eased risk with respect to years of ETS..exposure was t~und for a pooled subset of 385 cases, where most of the women were exposed at home as well as at work and~or socially. The aggregated group with combined exposures was then compared to cunuol~ who were neither exposed at work, nor at home. Apart from striking differences in life- style bct~een females belonging to these two different categories, the fact that the risk for women that wc~e solely exl',oscd at work (and/or in bars, etc.) cannot be deduced is a matter for concern. Based ou cotinine data, the Wold group makes an upwards adjustment of the estimated risks based on exp,,~ure of the reference group to ETS outside home. This approach would be: valid were it not for certain biochemical realities. There is a widespread misconception that cotinine determination in urine a~d saliva does provide an adequate q:mntitative measure of expomire to tobacco smoke. Unfortunately, this is not so. ~,.~:-r~s ther~~n-b~ ~b-~ou[~t that-cotinine determination in most case""-s ~,ughly-~s~r~t~ between active smokers and non-smokers, the quantitative correlation between nicotine tq~talc.e and cotinine levels is strikingly poor (Coultas et al., 1988) due to large inter-i,di~idual difl;"rences in the rate of nic~ihe-~'~:'/abbli~n{. Using personal samplers to replace notork, a~b' inaccm:,c indicators of exposures to ETS, like number of cigarettes smoked by spouse, etc., Phillips et al., ( I ')94, 1996) could confirm this conclusion, especially for low levels of ETS. In a co,tuolled stody by Neurath and Pein (1987), an 8-fold difference in cotinine levels could be demonstrated in snbjects who smoked exact~_the.._s~"of cigareUes per day (19) for 6 days. "I o avoid confounding by i~idiTv]~.~i ~moking varigt~les~(~h'~i~'tl-O~'~t-"~.-'(199g gave 2 mg nicotine orally by capsule to 124 healthy, unrelated, non-smoking volunteers (80 female). In spite of the fact that each subject had received exactly the same dose of nicotine, there was a 16-fold differe,ce bePaeen the highest and the lowest value for urinary excretion of cotinine during a 24 hour period. In a subsequent investigation genetic polymorpkism of the CYP2D6 gene (controlling for deb~i~oquine 4-hydroxylase) was found to be able to explain for this variability. These studies also provided an explanation for th;: ~i:t~viously repod~-d-faci th;i ~e s-t~bje~t~'(homozygous for CYP'~Dt~ mutations; poor metabolizers of debrisoquine and nicotine), who reported themselves as active smokers, I~_c.otinine le_.....___~vels below the CUt79.ff_level used to distinguish smokers from non- smokers (Jarvis et al., 1987; Lee, 1987; Pl~illips et al., 1996). Even if cotinine d,la were reliable, they were used by Hackshaw and co-workers (1997) in an inappropriate manner. These authors claim, that due to exposure outside home, non-smokers living with non-smokers have on the average cotinine levels that are one third of those for non-smokers living with smokers. In the more adequately performed epidemiological studies, individuals that were appreciably expnsed to ETS outside home were by study design not included among controls. Although some bias may have occurred due to false reporting, there is no justification to assume that "controls" in the epidemiological studies on ETS were on the average exposed to ETS at levels that were one third of those found in smoky homes. Hackshaw et al. 0997) further assurae that "nicotine from tobacco smoke is, for practical purposes, the only source of cotinine.', offering an explanation for the fact that individuals not exposed to ETS at home, exhibit a certain background level of cotinine in urine and saliva. Apart from the fact that methodological problems when determining very low levels of cotinine may have pla)'ed a role, there are other explanations. The content of nicotine in one kg of fresh tomatoes, bell peppers, or eggplants approximately cor~.es-~-d~o-~ng~-~d~t h~l~of,_~i~i~aret~e delivering about I mg of nicotine. Likewise, certain brands of tea and potato'~eel~ also~co~-n-t~a'in significant quanti~ nicotine (S~eea, 1988). in this context e.q~m¢--I'/o-~/~/~ intakes cannot be ignored in view of the fact that estimation by means of personal monitors have demonstrated that average ETS exposures in British homes of non-smoking subjects (Phillips ¢t al., 1994) was about 0.012 mg of nicotine pot da),, corr~spouding to the intake of 40 g of a mixture of fresh to-mat~e~ an"d"gYd~'t/~p~p~-'~O-n~3 ppm nicotine. The corresponding equivalent intakes for exposures in Swedish homes would--even lower (Phillips et al., 1995; 1996). An almost identical result is obtained using the estimate of Hackshaw et al. (1997). These authors assume that exposure to ETS is about 1% of that of a smoker with a relative risk of 19 (i.e. associated with 20 cigarettes per day and above). One third of I% of 20 x I mg equals 0.013 mg of nicotine. In conclusion, the upwards risk adjustment made by Hackshaw et al. (1997) for exposures of controls outside home must be considered as invalid. The Search for More Reliable Biomarkers of Exposure to Tobacco Smoke - Although not providing evidence applicable for long time abstainers, the measurement of adduces in haemoglobin could, in principle, extend the time period for estimating exposure to tobacco smoke from 1-2 days using cotinine as biomarker up to 4 months (the life time of the human erythrocyte) prior to sampling. Provided that diagnosis of lung cancer - that may cause drastic changes in life style - takes place within this period of time, more relevant estimates of current smoking habits could thereby be obtained. This principle has been attempted using adduces from 4-amoinobiphenyl. However, because of the lack .of__Jline~i~ in relation between exposure and the level of 4- aminobiphenyl adduces in ~'a~'~lobin, as ;,v-¢l~ as~s--~at ~nter.individual differences, this biomarker seems, unfortunately, to be less appropriate for dosimctri¢ purposes. Researchers at the Stockholm University (unpublished results) have found that acrylonitrile, a component of tobacco smoke, and that reacts directly with nucleophilic centres in pro~ more adequate for this propose. Bias in the Studies on ETS and Coronary Heart Disease - Only in two studies (Garland et al., 1985; Svendsen et al., 1987) seems there to have been attempts to validate the diagnosis, e.g. by assessment of autopsy material, and the notoriously unreliable death certificates were mostly used. Although the extent direction of" the bias inLroduced by this inadequacy may be difficult to predict, this deficiency underscores the presence of a general quality problem. The loss from the populations due to inadequate follow-up for the Hirayama (1981. 1984) and Sandier et at. 0989) prospective studies has already been mentioned. The prospective cohort study by Svendsen et at. (1987), including non-smoking men married to smoking wives, was on he other hand reasonably well designed. However, in addition to few recorded deaths, this study suffered from the drawback that the studied population was not representative of a normal population but was selected because these individuals were perceived to constitute a high-risk cohort. Further, "non-smokers" included never smokers as well as ex-smokers who quit prior to entry into the stud)'. As pointed out by Law et al. (1997), in contrast to what is the case for lung cancer the bias introduced by smoker misclassification is bound to be much smaller for the association between

exposu, c hJ ETS and hcan disease than for lung cancer, because the relative risk for ischacmic heart di.seasc in smokers is only around 2 as compared to 10-20 for heavy smokers. On the other hand, th:re is evidence that many smokers with CHD continue to smoke against the advise of their physici~ms, but tend not to reveal this fact (Lee, 19gg; Velicer et at., 1992; Suadicani et at. 1997). This represents a high-risk cohort, where smoker misclassification would have a relatively high in,pact. In many of the cohort studies information on smoking status was not obtained by persoual interviews, but solely by self-administered questionnaires, and special efforts to confirm the accura,'y ol" ~he exposure information were only made in three studies. To exclude -',,'five smokers, Tuns~ll-Pedoe et al. (1995) measured cotininc in serum. Exposure to EI'S v, as co~related with the presence of chronic respiratory distress, angina, CHD, and serum colinine. There was a significant association be~,een CHD and ETS of 1.6 (CI 1.1-2.4) based on sell:reported exposure, that was decreased to 1.2 (CI 0.9-1.7) when the association was based on cotininc dat~. For m~gina, the RR was 2.1 (11.1-3.9) based on self-reported exposure but only 0.8 (0.4-1.5} when based on cotinine measurements. For this reason, the authors suggest that the self- reported data cou~ld be biased due to the__ fact ~t~t i_udividu_al.Ls with symptoms tend to exaggerate exposure. Farther, ~haracterisati~-~exposure was ~'ot'~tisfaetory inasmuch as the selected individuals were asked if they had been exposed/not exposed to tobacco smoke "from someone else in the last duee days', but no information on previous active or passive smoking seems to have been collected. Confounding and Lung Cancer - Assuming a similar distribution of histological types of lung tumours for L'fS exposure as for active smoking, moa of the inc~ _a~e.~_in..._Kr__e ~y_~Ltumours, ~ only a parLo! t all--ochre_as could be ascribe tod-i~-~/scl~.~s[~i~ation. This directs the aUenti'~n to the possible role of confounding factors possibly associated with ETS exposure. Axnong the various l~ck~¢s taken into consideration, occupation, previous lung disease, and exposo~e to other air pollutants may have been serious sources of confounding in some of the smaller studies with few non-smoking cases as well as in some of the Asian studies. Further, it has been known since long that prcdisl,~:~ifion to lung cancer is influenced by hereditai3, factors (see e.g. literature cited by Roots et at., 1992), a fact that was n~d~-d'~'any significant extent in most of the studies on ETS. In several s~udies, like those of Fontham et al. (1991, 1994), adjustment for confounding factors often result,:d in downwards adjustments, but they were nol sufficiently large to "explain" the increased lung cancer risk in ETS-exposed individuals. The methodological errors involved in these adjusm~ats a~¢ illustrated below: Socio-economtcfactors of the type that is usually recorded (income, education) are causally only indirectl) rchtcd to lung cancer, because low social class is o~en associated with life-style factors, like inappr,~i,riate diet with low vitamin intake and high fat retake, a background of various diseases, hc=cditary disposition, etc., all of which can be more directly linked to lung cancer. A higher prevalence of,liseases of various kinds have been associated with low socio-economic status (Schmitz, 1973; Swedish Cancer Committee 1984a; Ehrenberg el al., 1985), and that has even been claimed to i**clude a~ll¢C_Cf_~hi_l~.o~..d~cancer (Ponle and Trichopolous, 1991). Thus, unequal inch*sion an~ong cases and controls of small groups of disease-proue indivi~d_.ual_s from, low socio-economic background may give rise to a consid~'ra-'b'l'e In many st~dics on ETS no matching for socio-economic variables was carried out, but when included it ~as usually can'ied out in a superficial manner. In the Fontham et al. (1991, 1994) studies, selection of a major par~ of the population based controls was e.g. carried out by random 16 digit dialling. As pointed out by Poole and TrichopouIos (1991), in U.$. persons of very low socio- economic status are difficult to identify, contact, and recruit as controls by this method, but such cases do appear for treatment in the type of hospitals from which the ETS cases were recruited by the Fontham group. Thus, in the Fontham et at. cohort, there were about 50% more cases than controls with household incomes below $ $,000. Further, around 60% m'h~'c~e-F-than controls ~d 1 not even have high schoOl ed~/,ti0n. Fdr ca~es-(or their spouses) belonging to this sub-set 16% lacked regular employment. The absence of such disease-pro~e cohorts from investigations ~:xp~surdg~ the-gvorl~plac6 may offer one explanation why, ia spite of considerable effo~, no significant association betxveen exposoro to ETS at the workplace and lung cancer has been in general been found. I! is important to rcalise that even when the "true" cause for a disease is causally urn'elated to ETS, but linked to life-style related factors that are associated with low social class correlated with exposure to ETS, adjusting for social class~ofie.___~ s~__~e._~yu..~de relative risk associated with ETS, but does not eliminate the association. Assume that the induction of lung cancer in non- smokin'~-~v-d'~'e-6-ff~-romo"'~-'61L~l-by-a-'c'~t-~'~ dietary factor that is inaccurately measured by social class. Misclassificatioo amounts to 20°A in both directions. Let us also assume that exposure to ETS does not affect the disease, but is correlated with the dietary factor in question. A c._~.~ associated with passive smoking of 1.31 is only reduced to 1.19 when the OR is standardized with respect to social class. In oth~/'~b'/" ,~cause the social~I~'-~ descriptor ina~mirrors the causative factor, an apparent association with the mother's sm_..._oki~ng is retained even after adjustment for social class (Lee, 1989; Tzonou, A. et al., 1986). Diet In a co-operative study between medical institutions in Hung Kong and the Karolinska Institute, Stockholm (Koo et at., 1988), the authors note that "Non-smoking families had healthier life-styles than wives with smo_.ki__qg.h.~an_~~, thereby~ngin~ into focus what may be e~i~u-ue nature of ~h~ ~ding that includes multiple risk factors including an unhealthy diet (Sidney et at., 1989; LeMarchand et al., 1991; Thornton et at., 1994). The negligible effects attributed e.g. by H~kshaw et al. (1997) to confounding by diet (2%) using flawed input data cannot be considered to be valid. ~ Mainly due to various methodological inadequacies, data have not always been consistent, but there is, nevertheless, convincing evidence demonstrating that intake of fruits and vegetables (carotenoids, vitamin A) as well as of selenium has a protective effect with respect to hing cancer incidence (See literature cited in Fraser et at.. 1991, St2~helin, et at., 1991, Candelora et al., 1992, .I and van den Brandt et at., 1993). Of main interest is the case-con~ol study including 124 cases of lJ histologically confirmed lung cancer in lifetime non-smoking women by Candelora et at. (1992). ~ Data from this investigation indicated, that high vegetable intake and intake of carotene had a s~ong~l protective effect. In comparison with the lowest qum'tile of consmnption, individuals in the highest[l[ quartile of vegetable consumption had the greatest decrease in risk with an OR of 0.2 (CI = 0. I-0.5). To obtain reliable information on diehaxy habits a superficial questionnaire is far fi'om adequate (IARC, 1990). According to Wynder (1993) of the A~nerican Health Foundation, investigations on food intake indicate the average individual to underreport caloric intake by 20%, and fat intake a bias of some 30% is not unusual. In those few ETS studies where dietary data had been collected and used for analysis, with the exception for llirayama's cohort study (1984a), they were all designed as case-control studies. As such they suffer from Lhe disadvantage fi~at dietary information nf reasonable reliability will be limited to the time period shortly before or after diagnosis. In view of the reD' long latency periods for induction of lung cancer, and due to changes in life styl~ caused by detection of the disease, su~'h information is obviously of little utility. Therefore, it is not 17

~.t~rprising that whereas e.g. Fontham et al. (1991, 1994), found an effect of diet' others did not. For tl~e cohort studied by Alavanja et al. (1993), where a striking association between lung cancer and intake of saturated fat was found, no effect of diet could initially be detected (Bmwuson et al., 1~92). As mentioned above, diagnosis of cancer may often precipitate d~astic changes in dietary habits as prescribed by the physician. In the subsequent follow-up of the Brown.son et al. (1992) cohort, an elaborate questionnaire was, therefore, used by Alavanja et at. (1993) in the in-home i nlerviews for all cases during a period of 4 years prior to the first diagnosis of lung cancer (a period d~cing which preclinlcal symptoms of disease should not have affected dietary practices). It would seem that in the studies reported by Fondmm et al. (1994), who similarly to some other investigators (Hirayama 1984a; Wu et al., 1985; Svensson et al., 1989; Kalandidi et at., 1990) found some protective effect of diet, this information had been collected and analyzed in a less than optimal f.ishion, and that a more adequate approach would most probably have greatly enhanced the extent ~,f confonnding by dielasy factors. I.,~w intake of fruit and vegetables may in itself constitute a risk factor, although the effects of the :,nti-c~rcinogcnic constituents in food arc evidently very complex, as illustrated e.g. by the failure of II.c._~Le~]~___lf to protec, t against cancer in a recent intervention stu__t.t.t.t.t.t.t~_(Hennekens et at., i 996). I lowev~r, in Western societies a lack ol ~'~ c-"~mtitucnts i--------'s often coupled to an increased i~takc of animat (saturated) fat (Wynder, t993; Becket, 1995), and smokers generally have a higher ~ht consumption and a lower intal~e of fruits and vegetables. This all means that if you live with a ~-,]oker, the fat consumption of that household v~uld be different than if you lived in a family that had no smoker in the household (Wynder, 1993). There is long-standing and well supported ~ ,-vidcnce, including five case-control studies and one cohort study, which link an increased risk of~ hmg cancer to increased fat intake (see literature cited in Aiavanja et al., 1993). Further,| ,-::perimental studies indicate that dietary fat can act as a promoter after trcaUncnt with an initiator | Iillirt, 1986; Birt and Pour, 1983; Beems and van Beck, 1954). g,~ :,a extensive case-control study comprising 429 non-smoking women with lung cancer and 1,021 , ,.~t~ols, including an in depth analysis of the possible role of various dietary factors (Alavanja et ~,1., 1993), passive smoking did not affect risk estimates. On the other hand dally intake of fat ii,~0.0~), saturated fat (jy=0.0004), oleic acid (p-~0.07), percent of calories fi'om fat (P=0.02) were ,aivariately associated (trend, p<0.10) with an increasing risk of lung cancer, while percent of , ~dories from carbohydrates (P---0.09) was associated with decreased risk. Whereas in previous ~,:vestigations. cholesterol and total fat consumption appeared to be relatively weak risk factors, this ~[udy revealed that they did not have an effect independent of satmated fat. Previously observed ,~,~dest decreases in risk associated with the consumption of vegetables and fruits could also be ,,,~#irmed. The relative risk among non-smoking women observed with increased saturated fatL~ .',ausumption was more than six-fold greater for the highest quintile than for the lowest quintile. Tbe~ • fleet of fal intake was more pronounced for edenocarcinoma than for other cell types. Fo~ .,denocarcinoma there was a l i-fold elevation in risk in the highest versus lowest quintiles ~ ~¢~trated fat consumption. Neither saturated fat intakc, nor selenium intake, was controlled for in~ ,'w of the epidemiological studies on ETS. It is somewhat surprising, that reviewers such ', .;fl~,m et al. (1994), Tr~daniel et at., 1994, and Hackshaw et at. (1997). fail to mention even the ~ ,~e~ce of the aforementioned study. • • ~,~ a possible linking of, on one hand high fat intake less healthy life style and exposure to ETS, • ~,,I on fl~e other, lung cancer, one could possibly object that no association with ETS was seen for .... • ,.t,l:~n cancer controls in the Fontham eta[. study (1991). However, apart f~om the fact that ,.,ihi,g is known about the actual fat intake for lhis group, no simple relationship exists between high ~at intake and colorectal cancer, where fibre intake (Weisburger, 1997) as well as hereditary factors like the recently identified non-polyposis colon cancer susceptibility gene a~e involved (Rumsby and Davies, 1995). In summary, it is difficult to define the hue extent of confounding due to dietary factors, but in light of the evidence cited above, this source of error could have been considerable, and together with misclassification of smoking status be of sufficient magnitude to explain virtually all increase in lung cancer in smoking women exposed to Confounding factors - ETS and Coronary Heart disease - Coronary heart disease (CHD) normally affects a considerable proportion of the non-tobacco using population, and a large number of risk factors other than tobacco smoke have been implicated. Some of these, such as many dietary factors, are the same as for the association between ETS and lung cancer. In a representative study of relative risks with respect to cardiovascular death conducted by Pfaffenberger et al. (1986), hypertension (RR=2.2; CI, 1.94-2.42) earned the highest risk followed by cigarette smoking (RR=I.84; CI, 1.64-2.04), history of parental CHD (RR=I.33; CI, 1.13-1.53), and sedentary life- style (RR-I.31; CI, 1.09-1.53). Other well recognized important factors are abnormal serura lipid patterns, diabetes, overweight, history of CHD, as well as a high fat diet coupled with a low intake of fruits and vegetables. Intakes of fruits and vegetables, aspirin as welt as of moderate quantities of alcohol have a protective effect. However, in most of the studies published on the relation between ETS and CHD cvcn many of the most common confounding risk factors were ignored. Out of 20 published studies no control of major confounding factors was carded out at all in o studies, intake of aspirin was not recorded in 19 studies, lack of exercise not in 17, a family histoD of heart disease or diabetes not in 16 studies, and social class and weight/obesity were not taken into account in I 1 studies. In 10 studies cholesterol in sen.an was ~neasured. Although considered to be a risk factor per se, it should be noted, however, that due to the operation of feedback mechanisms regulating cholesterol uptake and biosynthesis, the levels of this lipid in plasma is not a reliable index of dietary fat intake (Brown and Goldstoin, 1984). One of the most remarkable deficiencies with respect to confounding in this context, is that in spite of the universally recognized importance of dietary factors in preventing cardiovascular disease, information on diet (fat intake) was only collected in one (sic!) study. In the recent large U.S. studies, a number of confounding factors including social class, history of hypertension, weight, diabetes, dietary factors, alcohol, exercise, family history of heart disease were recorded. However, for the investigation by Layard (1995), as well as by Le "¢ois and Layard (1995), adjustment for such factors were said to have had little effect on the reported associations, but no specific data on such adjustments were presented. Steenland et al. adjusted for several important confounders, but failed to include dietary factors. Whereas a large number of risk factors have been associated with an increased risk of CHD, and while most of the required data for assessing the magnitude of bias introduced by such confounding in these studies are lacking, Law et al. (i 997) presented a highly conjectural estimate of an excess risk attributable to dietary differences and raised cholesterol values amounting to 6%. Based on small recorded differences among the scarce data available, other potential confounders were ignored by the authors as having little impact on the estimated risks. These authors also proposed a most unusual inte~reunion of the excess risk of 6"/* found in long-term tobacco abstainers, inasmuch as they believe this risk to "set an upper risk of confounding that is similar to our direct estimate of con founding." According to current concepts (Swedish Cancer Committ~, 1984a, 19