(CBS) It's no secret that having high blood pressure raises the risk for stroke. Now the authors of a new study say stroke risk may be dramatically elevated even for the one in three Americans whose blood pressure is only slightly elevated - a condition known as prehypertension.
Prehypertension is defined as a systolic blood pressure (top number) between 120 and 139 or a diastolic blood pressure (bottom number) between 80 and 89.
Just how elevated is the stroke risk? The study showed that prehypertensive people were 50 percent more likely than so-called "normotensive" people to suffer a stroke - even after age, gender, diabetes, obesity, smoking, and other risk factors were accounted for.
The risk was especially pronounced in young and middle-aged people, the study showed. Among people under age 65, those with prehypertension were nearly 80 percent more likely to suffer a stroke than those whose blood pressure is normal.
"These people may immediately benefit from blood pressure lowering methods, such as reducing their salt intake and weight, to help reduce their risk of stroke," study author Dr. Bruce Ovbiagele of the University of California, San Diego, said in a written statement. In an email to CBS News, he recommended against the use of blood pressure drugs for prehypertension - saying there was no evidence that drug therapy was beneficial for the condition.
Lowering elevated blood pressure is also known to help prevent other conditions associated with high blood pressure, which include heart attack and stroke.
The study - published in the Sept. 28 online issue of the journal Neurology - involved an analysis of 12 previous studies of stroke and blood pressure involving a total of 518,520 adults.
Stroke is an often disabling or deadly disruption of blood flow to the brain. It occurs when blood flow is blocked or when a blood vessel in the brain bursts, depriving brain cells of oxygen. Symptoms include sudden weakness or numbness on one side of the body, sudden loss of balance, sudden confusion or trouble speaking or understanding speech, dizziness, and trouble seeing in one or both eyes.
It's the number three cause of death, killing more than 130,000 Americans a year.
WebMD has more on prehypertension.