Even Mildly Elevated Systolic Blood Pressure Increases Risk of Stroke, UB Study Shows

BUFFALO, N.Y. -- People with only mildly elevated systolic blood pressure have a high risk of stroke similar to those with significantly raised systolic or diastolic blood pressure, long-term follow-up of a large national population sample has shown.

Moreover, the study found that the increase in stroke risk was not confined to those over 65, conventionally considered most stroke-prone: Systolic hypertension increased the risk of all types of strokes in participants as young as 45.

The study, headed by Adnan Qureshi, M.D., who conducted the research while associate professor of neurosurgery in the University at Buffalo School of Medicine and Biomedical Sciences and its Toshiba Stroke Research Center, appears in the December issue of Stroke.

Blood pressure is expressed as two numbers. The first number represents systolic pressure, the force blood exerts on vessel walls during the heartbeat. The second number represents diastolic pressure, the force on vessel walls between beats. A reading of 140/90 mm Hg is considered normal.

"For many years, elevated diastolic blood pressure was considered more important than elevated systolic pressure," said Qureshi. "However, the study highlights the importance of elevated systolic blood pressure in predicting the risk of stroke and stroke subtypes. It also suggests that even mild elevation of systolic blood pressure increases the risk of stroke and its subtypes.

"It is well known that isolated systolic hypertension in the elderly increases the risk of stroke and its subtypes," he noted. "Anti-hypertensive treatment has clear benefit for reducing stroke and stroke subtypes in this population with this type of hypertension.

"However isolated systolic hypertension is defined by a systolic blood pressure greater than or equal to 160 mm Hg. This study suggested that mild elevations in systolic blood pressure in the range of 140 to 159 mm Hg also increase the risk of stroke and its subtypes, although to a smaller magnitude, and that the risk pertains even to people in their 40s.

Qureshi and colleagues analyzed blood-pressure data and incidence of stroke from 12,344 participants aged 25-74 who took part in the first National Health and Nutrition Examination Survey (NHANES 1), conducted by the Centers for Disease Control between 1971 and 1975. These participants, a subset of the 32,000-person full study population, were contacted at four intervals after the initial data collection to obtain current health information. The last follow-up was conducted in 1992.

When participants were first interviewed, 493 had isolated systolic hypertension, (defined as a systolic blood pressure of 160 mm Hg or above and normal diastolic pressure); 1,241 had borderline isolated systolic hypertension (defined as systolic pressure between 140 and 159 mm Hg and normal diastolic pressure); and 3,954 had diastolic hypertension ( higher than 90 mm Hg). In the intervening years, 825 persons experienced some type of stroke.

Analyzing stroke events with baseline blood pressure readings and other variables, researchers found that participants who had isolated systolic hypertension at baseline were nearly three times more likely to have had any kind of stroke than participants with normal blood pressure. This statistic translated into a rate of 17.4 strokes per 100 people.

Participants with borderline isolated systolic hypertension had about a 1.5-times greater risk of stroke, for a stroke rate of 9.5 per 100. The stroke rate for those with diastolic hypertension was 10 per 100.

"The risk of either ischemic stroke (caused by a blocked vessel in the brain) or intracerebral hemorrhage was higher in persons with both types of systolic hypertension," Qureshi said. "The risk of those with moderately elevated systolic pressure was nearly as high as for those with diastolic hypertension.

"We've found that middle-aged persons with elevated systolic pressure have an increased risk for stroke similar to that of the elderly population," he said. "These results suggest that treatment with anti-hypertensive medication may be required at a lower threshold than previously thought, and that middle-aged persons should be considered for screening and treatment."

Also participating in the UB study, all from the Department of Neurosurgery, were M. Fareed K. Suri, M.D.; Yousef Mohammad, M.D. (now at Ohio State); Lee R. Guterman, Ph.D., M.D., and L. Nelson Hopkins, M.D., department chair. Qureshi now is at the University of Medicine and Dentistry of New Jersey.