Passive smoking and heart disease
Authors: M. E LeVois, M. W Layard, P. Lee, R. Dempsey, K W E Denson, M R Law, J K Morris, N J Wald
Journal: BMJ (1998)

Editor—In their meta-analysis Law et al1-1 reject results we published1-2,1-3 on environmental tobacco smoke and coronary heart disease, using data from the two large cancer prevention studies by the American Cancer Society and the national mortality followback survey. They reject our results because they disagree with our interpretation of data from other studies and because our analysis was funded by the tobacco industry (table ​(table1).1). 



Table 1

Data rejected by Law et al for their meta-analysis of spousal smoking and mortality from coronary heart disease in cancer prevention study I.1-2 Values are relative risks (95% confidence intervals)



By excluding our results Law et al discard 16 280 relevant deaths from coronary heart disease with spousal smoking data and retain 6600 cases. They give no hint that their meta-analysis includes under a third of the available published data. The reasons for rejecting so many data should be considered. If Law et al believe we have misrepresented the data, they should analyse the same data from the American Cancer Society and the national mortality followback survey, and report their results. 

Law et al’s argument that our data from the second cancer prevention study disagree appreciably with data reported by Steenland et al1-4 is wrong.1-5 They incorrectly compare our results for ever-smoking spouse exposure with Steenland et al’s results for current-smoking spouse exposure. Both studies present comparable results for subjects in the second cancer prevention study who are married to a current smoker. We calculate the relative risk for men to be 1.30 (95% confidence interval 1.11 to 1.51), for women 1.08 (0.89 to 1.32), and for both sexes combined 1.21 (1.07 to 1.37). These results are similar to those reported by Steenland et al (men 1.22 (1.07 to 1.40), women 1.10 (0.96 to 1.27)),1-4 which we have combined to give a relative risk of 1.16 (1.05 to 1.27) for both sexes. 

Both sets of analyses report a barely significant association between environmental tobacco smoke and coronary heart disease in men, with a negative dose response. There is no significant association between spousal smoking and death from coronary heart disease in women, nor any sign of a dose response. Nearly twice as many women as men died of coronary heart disease in the second cancer prevention study, which makes the data for women particularly relevant to any meta-analysis. 

Law et al’s selective rejection of two thirds of the relevant data on environmental tobacco smoke and coronary heart disease raises additional questions about their interpretation of other data. We have noted significant publication bias in the pooled results on environmental tobacco smoke and coronary heart disease, for example.1-2 In reaching the opposite conclusion, Law et al ignore the significant association between study size and relative risk in the previously published spousal smoking studies as well as the significant difference between published and unpublished results on environmental tobacco smoke and coronary heart disease.