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 risk of stroke associated with current smoking (active smoking) using the traditional baseline group (never-smokers) and a baseline group that includes lifelong non-smokers 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 Auckland, New Zealand. SUBJECTS: Cases were obtained from the Auckland stroke study, a population-based register of acute stroke. Controls were obtained from a cross-sectional survery of major cardiovascular risk factors measured in the same population. A standard questionnaire was administered to patients and controls by trained nurse interviewers. RESULTS: Information was available for 521 patients with first-ever acute stroke and 1851 community controls aged 35-74 years. After adjusting for potential confounders (age, sex, history of hypertension, heart disease, and diabetes) using logistic regression, exposure to ETS among non-smokers and long-term ex-smokers was associated with a significantly increased risk of stroke (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 risk of stroke compared with people who reported they had never smoked cigarettes (OR = 4.14; 95% CI = 3.04 to 5.63); the risk increased when active smokers were compared with people who had never smoked or had quit smoking more 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 between 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 exposed to ETS are excluded from the non-smoking reference group. These findings also suggest that studies investigating the adverse effects of smoking will underestimate the risk if exposure to ETS is not taken into account.