Even high-but-normal blood pressure elevates stroke risk

People with pre-hypertension have a 55-per cent higher risk of experiencing a future stroke than people without pre-hypertension, report researchers at the University of California, San Diego School of Medicine in a new meta-analysis of scientific literature published in the September 28 online issue of the journal Neurology.

Pre-hypertension is clinical category created by experts in 2003 to describe patients whose blood pressure was elevated, but still considered within normal range.

Hypertension or abnormally high blood pressure is a major risk factor for cardiovascular disease and strokes, but much less is known about the health threat posed of pre-hypertension, which is defined by a systolic pressure reading between 120 and 139 mmHg (the top number) and a diastolic reading between 80 and 89 mm Hg (the bottom number)

''The experts reasoned that, generally speaking, the higher the blood pressure, the greater the risk of death and disease, possibly starting from within the normal blood range,'' said Bruce Ovbiagele, MD, professor of neurosciences at UC San Diego School of Medicine and senior author of the study.

However, Ovbiagele said, conclusive evidence was lacking, ''so we decided to compile all the published studies in the scientific literature to date, and using statistical techniques find out if there is indeed a higher risk of future stroke in people with pre-hypertension, the extent of that risk, and whether particular characteristics were associated with higher stroke risk.''

The researchers identified 12 relevant prospective cohort studies of pre-hypertension. All of the studies were derived from the general population. Four were from the United States, five from Japan, two from China and one from India. Combined, the studies involved more than 518,000 participants and covered periods ranging from 2.7 years to 32 years, with stroke occurrences documented. The prevalence of pre-hypertension in the studies ranged from 25 to 46 percent. In the United States, it's estimated roughly one-third of adults have pre-hypertension.