1 Department of Community Medicine, University of Hong Kong, 21 Sassoon Road, Pokfulam, Hong Kong, China,2 Department of Health, Student Health Service, 4/F Lam Tin Polyclinic, Kowloon, Hong Kong, China,3 Nuffield Department of Clinical Medicine, University of Oxford, Oxford OX2 6HE Introduction Passive smoking can cause death from lung cancer and coronary heart disease, but there is little evidence for associations with other causes of death in never A recent study showed increased all cause mortality with exposure to secondhand smoke at home but did not examine associations with specific causes of death and dose-response 1 We have published estimates of the mortality attributable to active smoking in Hong Kong2 and now present the related findings on passive smoking at Participants, methods, and results Details of the sample selection and data collection have been 2 Each person who reported a death in 1998 at four death registries was given a questionnaire which asked about the lifestyle 10 years earlier of the decedent and of a living person about the same age who was well known to the Passive smoking was identified in the interview with the question, "Ten years ago, in about 1988, excluding the decedent/control, how many persons who lived with the decedent/control smoked" Decedents or controls who lived with one or more smokers were classed as Cause of death was obtained from the death We selected never smoking decedents and controls aged 60 years or over because there were few younger To avoid selection bias, we included only cases and controls who had a living spouse at the time of We used logistic regression to derive odds ratios adjusted for age and education, and for sex when men and women were What is known on this topic There is strong evidence that passive smoking is causally associated with death from lung cancer, coronary heart disease, and all causes, and also with acute stroke What this study adds The dose-response relation between passive smoking and mortality from stroke and chronic obstructive pulmonary disease, as well as from lung cancer, ischaemic heart disease, and all causes of death, strengthens the causal link We identified 4838 never smoking cases (55% male) and 763 never smoking controls (55% male) All controls were used in the analysis for each specific cause of We found significant dose dependent associations between passive smoking and mortality from lung cancer, chronic obstructive pulmonary disease, stroke, ischaemic heart disease, and from all cancers, all respiratory and circulatory diseases, and all causes (table) The association between mortality and passive smoking did not differ between males and Deaths due to injury or poisoning were not associated with passive Number of subjects who were or were not exposed to secondhand smoke at home and odds ratios (adjusted for age and education, and for sex when men and women were combined) for mortality in people aged 60 or over, Hong K Values are odds ratio (95% confidence interval) unless indicated otherwise Comment Dose dependent associations between passive smoking and causes of death are consistent with previous findings for lung cancer and coronary heart disease and extend the evidence on Previous studies have shown associations between passive smoking and first acute strokes,3 4 and we have now shown a dose-response relation with mortality from Previous studies focused on ischaemic strokes but Chinese populations have a greater incidence of haemorrhagic stroke than do white populations,5 implying that many of the strokes in our study may have been non- Passive smoking probably affects all stroke subtypes, as does active Our finding of a 34% increase in all cause mortality is consistent with but higher than that (15%) in the New Zealand 1 Exposure to secondhand smoke at home is higher in Hong Kong than in New Zealand due to crowded living Before the 1990s, awareness of the danger of passive smoking was lower and smokers smoked freely at We focused on passive smoking at home because the proxy reporter could most reliably supply these data, and we adjusted for education, which was also reliably recorded2 and is a good proxy for social class in Hong K As data on cases and controls were derived from the same proxy, reporting bias should be 2 If our results are not due to residual confounding, they provide further evidence that the dose-response associations between passive smoking and stroke and all cause mortality are likely to be See Editorial by Kawachi This article was posted on on 27 January 2005: We thank W L Cheung for help with analysis; the Immigration Department of the Government of the Hong Kong Special Administrative Region for data and assistance; and, in particular, the relatives who provided Contributors: THL, SYH, AJH, KHM, and RP designed and carried out the study on which this analysis was based; SMcG, MS, LMH, and GNT planned and carried out this analysis; and all authors contributed to writing the SMcG and THL are Funding: Hong Kong Health Services Research Committee (#631012) and Hong Kong Council on Smoking and H Competing interests: THL is vice chairman and AJH a former chairman of the Hong Kong Council on Smoking and H Ethical approval: Ethics Committee of the Faculty of Medicine, University of Hong K References Hill SE, Blakely TA, Kawachi I, Woodward A Mortality among never smokers living with smokers: two cohort studies, 1981-4 and 1996- BMJ 2004;328: 988- Lam TH, Ho SY, Hedley AJ, Mak KH, Peto R Mortality and smoking in Hong Kong: case-control study of all adult deaths in BMJ 2001;323: 361- Bonita R, Duncan J, Truelson T, Jackson RT, Beaglehole R Passive smoking as well as active smoking increases the risk of acute Tobacco Control 1999;8: 156- Iribarren C, Darbinian J, Klatsky AL, Friedman GD Cohort study of exposure to environmental tobacco smoke and risk of first ischemic stroke and transient ischemic Neuroepidemiology 2004;23: 38- Kay R, Woo J, Kreel L, Wong HY, Teoh R, Nicholls MG Stroke subtypes among Chinese living in Hong Kong: the Shatin stroke Neurology 1992;42: 985-