People who smoke even occasionally are more likely than nonsmokers to have a serious type of stroke caused by a ruptured blood vessel — 27 percent more likely if they smoke up to 20 packs a year, according to research published in the journal Stroke. The average American smoker, according to the Centers for Disease Control and Prevention, smokes 14 cigarettes daily, which means about 255 packs a year. The type of stroke examined by the researchers, known as a subarachnoid hemorrhage, occurs when a weakened blood vessel ruptures and bleeds into the space between a person’s brain and skull. Most often, this results from an aneurysm, an abnormal bulge in a blood vessel. A subarachnoid hemorrhage is not as common as an ischemic stroke, which is caused by a blood clot, but it also can lead to neurological problems or be life-threatening without immediate treatment to stop the bleeding. To focus on the effect that smoking may have on people’s risk for this type of stroke, the researchers analyzed data on 408,609 adults, about a third of whom smoked regularly. During the study period, 904 participants had a subarachnoid hemorrhage. The more people smoked, the greater their risk for this type of stroke, prompting the American Stroke Association to note that the findings “provide evidence for a causal link” between smoking and subarachnoid hemorrhage.