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.
- Copyright © 1998 by American Heart Association
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.
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.
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.