According to a recent article in the British Medical Journal stroke remains the third leading cause of death in most Western countries. Many epidemiological studies have established cigarette smoking as an important risk factor for stroke. Until recently, however, this relation was based on observational studies. We now have definite evidence that smoking itself has a direct causal effect on stroke.

The relation between smoking and atherosclerosis was observed as early as 1908. The earliest report associating stroke and extracranial arterial disease was in 1875.

The Framlingham Heart Study was among the first to assess these the relation of smoking to type of stroke, number of cigarettes smokes, and the effect of stopping. It concluded that smoking made a significant independent contribution to the risk of stroke generally and to brain infarction specifically. The relative risk of stroke in heavy smokers (40 cigarettes a day) was twice that of light smokers (10 cigarettes a day), and the risk of stroke increased with the number of cigarettes smokes; cessation lowered the relative risk ration to that of a non-smoker. This reduction in risk ratio was significant by two years after stopping and had reached the level of a non-smoker after five years.

Heavy smokers have a relative risk of stroke 2-4 times greater than non -smokers. The association between the number of cigarettes smoked and the increase in the risk of stroke remains inconclusive. Also after five years there was no further benefit. Risk reduction is dependent on the quantity of cigarettes smoked before stopping: light smokers (20 cigarettes a day) reverted to normal values, but heavy smokers retained twice the incidence of stroke as non-smokers.

Secondary pipe or cigar smokers still have an increased risk similar to that of light smokers, so switching to a pipe or cigars confers little benefit.

The relative risk of stroke among hypertensive smokers if five times that among normotensive smokers, but 20 times that of normotensive non-smokers. The greatest benefit in stopping smoking is among hypertensive heavy smokers. Cigarette smoking is thus a definite independent risk factor for stroke, particularly ischaemic stroke. The evidence for casual association between cigarette smoking and extracranial carotid aterosclerosis is abundant. All smokers who stop smoking will benefit from reducing their risk of ischaemic stroke, irrespective of the degree of previous exposure to smoking.