Even people whose blood pressure is slightly higher than normal may have a significantly increased risk of stroke, finds a new review of past research.

High blood pressure, or hypertension, is known to be a powerful predictor of a person's risk of stroke and heart disease. But less has been understood about the health consequences of prehypertension, which affects about one-third of American adults. The new study, published in the journal Neurology, suggests that prehypertensive people have on average a 55% greater risk of stroke than those with normal blood pressure.