Meta-analysis of relation between cigarette smoking and stroke.

There is a lack of consensus among studies on the possible risks of stroke from cigarette smoking; because of this a meta-analysis was conducted. All published data on the association were sought and the relative risk for each study obtained whenever possible. The pooled relative risks were calculated by using estimates of the precision of the individual relative risks to weight their contribution to the meta-analysis. Thirty two separate studies were analysed. The overall relative risk of stroke associated with cigarette smoking was 1.5 (95% confidence interval 1.4 to 1.6). Considerable differences were seen in relative risks among the subtypes: cerebral infarction 1.9, cerebral haemorrhage 0.7, and subarachnoid haemorrhage 2.9. An effect of age on the relative risk was also noted; less than 55 years 2.9, 55-74 years 1.8, and greater than or equal to 75 years 1.1. A dose response between the number of cigarettes smoked and relative risk was noted, and there was a small increased risk in women compared with men. Ex-smokers under the age of 75 seemed to retain an appreciably increased risk of stroke (1.5); for all ages the relative risk in ex-smokers was 1.2. The meta-analysis provides strong evidence of an excess risk of stroke among cigarette smokers. Stroke should therefore be added to the list of diseases related to smoking.