Clot clout.

The carotid arteries supply most of the brain's blood; clots here are the most damaging form of ischemic stroke.

• being male (but stroke kills more women)
• being African-American
• smoking cigarettes
• being overweight
• having high blood pressure, heart disease or diabetes.

(Need stroke stats?)

Large numbers of people are vulnerable to stroke. Researchers in New York State found major blockages in carotid arteries -- the brain's major blood source -- among 18 percent of people screened at health fairs and malls. The study measured blood movement with ultrasound equipment.

Adnan Qureshi, of the department of neurosurgery at Syracuse University-New York Medical Center at Buffalo, says questions about risk factors showed that people older than 65 were 4.1 times as likely to have impaired circulation to the brain. Smoking doubled the risk, and heart disease raised it by a factor of 2.4. These numbers may not represent the general population, Qureshi cautions, because the people were not chosen at random. However, they do help identify who might benefit from screening for surgery to open arteries to the brain. Artery-reaming surgery, he says, can reduce the chance of a stroke over the next five years.

The most common strokes start with a loss of blood supply. Why not bust the clots and move the blood?