Passive smoking as well as active smoking increases the risk of acute stroke

Objective-To estimate the relative risk of stroke associated with exposure to environmental tobacco smoke (ETS, passive smoking) and to estimate the r isk of stroke associated with current smoking (active smoking) using the tr aditional baseline group (never-smokers) and a baseline group that includes lifelong nonsmokers and long-term (>10 years) ex-smokers who have not been exposed to ETS. Design and setting-Population-based case-control study in residents of Auck land, New Zealand. Subjects-Cases were obtained from the Auckland stroke study, a population-b ased register of acute stroke. Controls were obtained from a cross-sectiona l survey of major cardiovascular risk factors measured in the same populati on. A standard questionaire was administered to patients and controls by tr ained nurse interviewers. Results-Information was available for 521 patients with first-ever acute st roke and 1851 community controls aged 35-74 years. After adjusting for pote ntial confounders (age, sex, history of hypertension, heart disease, and di abetes) using logistic regression, exposure to ETS among non-smokers and lo ng-term ex-smokers was associated with a significantly increased risk of st roke (odds ratio (OR) = 1.82; 95% confidence interval (95% CI) = 1.34 to 2. 49). The risk was significant in men (OR = 2.10; 95% CI = 1.33 to 3.32) and women (OR = 1.66; 95% CI = 1.07 to 2.57). Active smokers had a fourfold ri sk of stroke compared with people who reported they had never smoked cigare ttes (OR = 4.14; 95% CI = 3.04 to 5.63); the risk increased when active smo kers were compared with people who had never smoked or had quit smoking mor e than 10 years earlier and who were not exposed to ETS (OR = 6.33; 95% CI = 4.50 to 8.91). Conclusions-This study is one of the few to investigate the association bet ween passive smoking and the risk of acute stroke. We found a significantly increased risk of stroke in men and in women. This study also confirms the higher risk of stroke in men and women who smoke cigarettes compared with non-smokers. The stroke risk increases further when those who have been exp osed to ETS are excluded from the non-smoking reference group. These findin gs also suggest that studies investigating the adverse effects of smoking w ill underestimate the risk if exposure to ETS is not taken into account.