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Blood pressure at the high end of ‘normal’ range may be linked to stroke risk

Sept. 30, 2011

By Patricia Nicholson

Blood pressure that’s even a little bit high may be a bigger health risk than previously believed. A new study suggests that people with “prehypertension” – blood pressure that’s slightly elevated, but not high enough to qualify as hypertension, or high blood pressure – have a 55 per cent higher risk of stroke compared to people with optimal blood pressure.

The study defined prehypertension as blood pressure between 120 and 139 mm Hg systolic (the top number) and 80 to 89 mm Hg diastolic (bottom number). Numbers above those readings qualified as hypertensive, or high blood pressure.

Prehypertension is very common.

To find out whether prehypertension had any effect on stroke risk, researchers at the University of California and Chang Gung University College of Medicine in Taiwan pooled results from 12 studies that included a total of more than 500,000 people. All of the studies measured blood pressure at the beginning of the study, and followed the participants for anywhere from 2.7 years to more than 30 years, assessing stroke incidence during that followup period.

In each of the studies, at least 25 per cent of the participants had prehypertension, and in some studies the prevalence was as high as 46 per cent.

The researchers found that prehypertension was associated with a 55 per cent increase in stroke risk. They then analyzed results of a subgroup of seven studies that distinguished between low prehypertension (120-129 mm Hg or 80-84 mm Hg) and high prehypertension (130-139 mm Hg or 85-89 mm Hg). They found no significant stroke risk associated with low prehypertension, but high prehypertension was associated with a 79 per cent increased risk of stroke.

The Public Health Agency of Canada (PHAC) defines optimal blood pressure as 120 over 80, although normal blood pressure is classified as any measurement under 130 systolic and 85 diastolic. PHAC classifies systolic measurements from 130-139 and diastolic from 85 to 89 (the same range the study authors designate as high prehypertensive) as “normal high.”

The results of the study suggest that this “normal high” group has a 79 per cent higher risk of stroke compared to people with optimal blood pressure, even though their blood pressure is not elevated enough to qualify as hypertension.

PHAC reports that high blood pressure affects almost one-quarter of Canadians, is the most common reason for doctor’s visits, and the number one reason for taking medication.

The study appears in the Oct. 4, 2011 issue of the journal Neurology.

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  • A publication of:
  • Women's College Hospital