That's the finding of a Japanese study in the March 3 online issue of Circulation.
The morning blood pressure surge is also linked to brain lesions known as silent strokes.
This is the first study to show that a morning spike in blood pressure is a predictor of stroke in elderly people with high blood pressure.
The study included 519 people, average age 72, with high blood pressure. They were monitored by the researchers for an average of 41 months.
All the participants were given ambulatory blood pressure monitoring and had a magnetic resonance scan (MRI) to look for the presence of silent cerebral infarcts -- the brain lesions that indicate a silent stroke.
To calculate morning blood pressure surge, the researchers measured average systolic blood pressure during the two hours after the subject woke up and subtracted the average systolic blood pressure during the hour that included the person's lowest sleeping blood pressure. Systolic pressure is the top number in a blood pressure reading.
The study volunteers were divided into two groups. The morning surge (MS) group included 53 people who had a morning blood pressure increase of 22 mmHg (millimeters of mercury) or more. The other group included people with a lower morning blood pressure increase.
People in the MS group were 57 percent more likely to have multiple silent strokes than the non-MS group (33 percent). The study also found that 19 percent of the people in the MS group had stroke in the follow-up period, compared to 7.3 percent of the non-MS group.
In general, a 10 mmHg hike in morning blood pressure increased stroke risk by 22 percent.
The findings suggest this morning blood pressure surge could be a new target for drug treatment.
Here's where you can learn more about stroke.