Until recently, however, this relation was based on observational studies and the
effects of smoking were thought to be synergistic with hypertension, diabetes mellitus, glucose intolerance, age, hypercholesterolaemia, and pre-existing cardiovascular disease.
Now we have definite evidence that smoking itself has a direct causal effect on stroke.
Cigarette smoking is thus a definite independent risk factor for stroke, particularly ischaemic stroke.