Stroke risk increases with even small rises in blood pressure

By Dr. Ananya Mandal, MDSep 29 2011

Small rises of blood pressure may greatly increase 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 a total of 518,520 adults.

The analysis revealed that 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.

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.

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.

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.”

“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.”

“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.

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. “It could be similar to what happened with cholesterol numbers,” says Seemant Chaturvedi , director of the stroke program at Wayne State University and a fellow of the American Academy of Neurology. “Everyone knows those have been racheted down.”

Physician Karen Furie, who is not associated with study, says pre-hypertension is a “very plausible risk factor for stroke,” adding it does often lead to hypertension, which can damage and weaken artery walls. “The significance of this paper is that it represents the synthesis of roughly a half million subjects,” says Furie, a fellow of the American Academy of Neurology. “The conclusions appropriately call for additional studies. Confounders [variables] such as insulin resistance (pre-diabetes), sedentary lifestyle, obesity, alcohol consumption, and dietary factors, all related to stroke risk, could not be adequately addressed in this analysis,” he said.