(Circulation. 1998;97:1870-1871.)
© 1998 American Heart Association, Inc.
A Prospective Study of Passive Smoking and Coronary Heart Disease
C. R. E. Coggins, PhD;
; DABT
Lorillard Tobacco Co,
Greensboro, NC
To the Editor:
A recent article1 on environmental tobacco smoke
(ETS) and coronary heart disease (CHD) contains conclusions
that are not supported by the scientific data.
Among other failings, the data are based entirely on the answer to a
single question asked 15 years ago on current "exposure." There is
only scant discussion of the subsequent validity of the findings to the
present day, in which smoking restrictions in the workplace are
very common. Even though the authors used additional questionnaires
every 2 years (to assess cardiovascular risk factors
and the occurrence of major illnesses), for some reason they did not
think it necessary to ever repeat the question on current
"exposure." As in virtually all epidemiologic studies on ETS,
actual exposure was not determined. However, the surrogate used to
assess exposure in this study is especially weak.
Of the 17 multivariate relative risks
presented, no less than 11 (65%) could be the result of chance
alone, because the confidence interval presented includes the
null (in which the disease incidence would be the same in exposed and
nonexposed groups). The remaining 6 relative risks have lower
confidence limits that are above 1 (and are thus statistically
significant), but the associations are extremely weak. The results of
the Kawachi study are thus in very close agreement with those from the
much larger cohort in the American Cancer Society's CPS-II
study.2 It is important to note that neither of
these two studies shows a statistically significant value for
coronary heart disease in women "exposed" to smoke at work.
Indeed, the authors of the CPS-II study concluded that their findings
"do not show consistent dose-response trends and are possibly
subject to confounding by unmeasured risk factors." The
same may well be said of the Kawachi study.
Implausibly, the relative risks presented are only slightly
smaller than the value of 1.78 that was reported in CPS-II for CHD in
current female smokers aged 35 and above.3
Layard4 combined the ETS results of the CPS-II
study with two other similar studies to produce a data set with
>19 000 CHD cases (compared with 152 cases in the Kawachi study). The
pooled relative risk for this data set was 1.00, with a 95% confidence
interval of 0.97 to 1.04, a statistically nonsignificant finding that
the Kawachi report fails to mention.
The recent statement5 "by scientific standards,
the weight of evidence continues to falsify the hypothesis
that ETS exposure might be a coronary heart disease risk
factor" clearly remains valid.
References
-
Kawachi I, Colditz GA, Speizer FE, Manson JE, Stampfer MJ,
Willett WC, Hennekens CH. A prospective study of passive smoking and
coronary heart disease. Circulation. 1997;95:2374–2379.[Abstract/Free Full Text]
-
Steenland K, Thun M, Lally C, Heath C Jr. Environmental tobacco
smoke and coronary heart disease in the American
Cancer Society CPS-II cohort. Circulation. 1996;94:622–628.[Abstract/Free Full Text]
-
DHSS. Reducing the health consequences of smoking: 25 years of
progress: a report of the Surgeon General. Rockville, Md: Centers for
Disease Control, Office on Smoking and Health; 1989:151.
-
Layard MW. Ischemic heart disease and spousal smoking
in the National Mortality Followback Survey. Regul Toxicol
Pharmacol. 1995;21:171–180.
-
Gori GB. Environmental tobacco smoke and coronary heart
syndromes: absence of an association. Regul Toxicol
Pharmacol. 1995;21:281–295.[Medline]
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