Even slightly elevated blood pressure greatly increases a person's risk of stroke, according to new research.
The study review, published in the journal Neurology, analyzed the results of 12 studies on blood pressure and stroke incidences among more than half a million adults.
In the study, those who had prehypertension -- defined as a systolic blood pressure (the top number) of 120 and 139 mmHg or a diastolic blood pressure (the bottom number) between 80 and 89 mmHg -- were about 50 percent more likely to suffer a stroke than people with healthy blood pressure levels.
The results held true even after researchers accounted for other risk factors, including age, diabetes, obesity and smoking. Patients under the age of 65 with prehypertension were nearly 80 percent more likely to develop a stroke than people with normal blood pressure.
Researchers added that stroke risk appeared to be more driven by systolic blood pressure than diastolic in the study findings.
"People who have prehypertension are at higher future risk of stroke," said Dr. Bruce Ovbiagele, director of the Olive View-UCLA Stroke Program and lead author of the study. "We also saw that not all prehypertesnion is created equal. For those who fall into the higher range of prehypertension, there seems to be an especially high risk."
In 2003, the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure proposed the word "prehypertension" to describe the numbers between normal and high blood pressure. Today, about one in three American adults suffer from slightly higher-than-normal blood pressure.
"This study is of considerable interest and points out what many of have believed for some time -- that is, blood pressure thresholds are arbitrary and do not, per se, establish a quantifiable risk for the individual patient, but rather reflect the risk in a population," said Dr. Domenic Sica, chairman of clinical pharmacology and hypertension at Virginia Commonwealth University. "Therefore, quantifying risk may be useful [to] guide the clinician on selecting a drug therapy in someone in whom life-style measures are inadequate."
Ovbiagele was quick to note that drug therapy should not be the first option, at least yet, for people who suffer from prehypertension.
"People who do fall into the higher range of prehypertension should modify their lifestyle as much as possible," said Ovbiagele. "Get to an ideal weight, stop smoking, restrict salt -- these changes in lifestyle are relatively harmless and help not only high blood pressure, but other problems, like heart attack and kidney failure."
"Sleep can have a meaningful effect in lowering blood pressure and the converse," said Sica, "this can mean both the quantity and quality of sleep."
Dr. Matthew Lucks, a San Diego-based cardiologist, noted that the more than two alcoholic beverages per day in men and more than one per day in women can significantly increase blood pressure.
"Clearly, the systolic blood pressure goals are not one size fits all, but there is significant benefit to the young and middle-aged population that achieving the lowest possible systolic blood pressure can reduce cardiovascular events and stroke," said Lucks.
Blood pressure readings vary throughout the day -- higher when first waking up, lowering in the morning then going up a little in the morning before typically dropping off while asleep -- and it's important to take these rhythms into account when measuring stroke risk, experts said.
Obviagele and colleagues plan on conducting a clinical trial to compare prehypertension patients who receive drug therapy versus those who do not in order to understand the need for medication among the prehypertension population.
"The conclusions of the study do leave the door open for a new definition and goal for prehypertension," said Lucks.