ISLAMABAD    -   Researchers in Finland found a link between smoking and subarachnoid hemorrhage (SAH), a type of bleeding stroke, in a study of more than 16,000 pairs of twins over 42 years. The study found that bleeding in the brain can be explained to a greater degree by environmental risk factors, such as smoking, than by genetic influence. 

An investigation of the Finnish Twin Cohort reaffirmed a link between smoking and subarachnoid hemorrhage (SAH), a type of bleeding stroke that occurs under the membrane that covers the brain and is frequently fatal. The new study by researchers in Finland is published recently in Stroke, a journal of the American Stroke Association, a division of the American Heart Association. 

In a 2010 study of nearly 80,000 twins from Denmark, Finland and Sweden, results suggested that SAH had more to do with external risk factors and very little to do with genetic influence. 

Twins share either all or half their genes (identical vs. fraternal) so they are valuable for studies designed to evaluate the role of genetics versus environmental factors in disease development.