Any head injury — even a mild one — raises a person’s risk of later having an ischemic stroke.

Having multiple injuries increases that risk, even more so than the severity of a single traumatic brain injury (TBI), researchers report.

"Our study found that those who experience two or more head injuries, including even mild head injuries, are at higher risk of subsequent ischemic stroke,” said study author Dr. Holly Elser, a neurology resident at the Hospital of the University of Pennsylvania in Philadelphia. “The findings underscore the importance of public health interventions to reduce the risk of head injury, as well as measures aimed at stroke prevention among individuals with a prior head injury.”

An ischemic stroke, the most common type of stroke, is caused by a blockage in the vessels that supply blood to the brain. TBIs can be mild, moderate or severe.

To study the connection with stroke, the researchers analyzed data from the Atherosclerosis Risk in Communities (ARIC) study of more than 12,800 U.S. adults. The diverse group had not had a head injury or stroke when the study began in 1987.

More than 2,100 of those people did experience a head injury during the following 30-year time period, about 73% of which were mild.

More than 140 had an ischemic stroke.

The investigators found that those who had a head injury had a 32% increased risk of ischemic stroke. Those with two or more head injuries had a 94% increased risk of ischemic stroke compared to those with no head injury. Age, race or sex didn’t matter.

This underscores the importance of preventing head injuries, according to the study authors.

The findings were presented Tuesday at the American Neurological Association annual meeting in Philadelphia. Findings presented at medical meetings should be considered preliminary until published in a peer-reviewed journal.

TBIs may increase the risk of stroke by damaging tiny blood vessels in the brain, the cells lining those blood vessels and the inner layer of arteries, past research has shown. This damage can block or slow blood flow in the brain.

“Our results emphasize the importance of measures that prevent head injury, like always wearing seatbelts in the car and wearing a helmet while biking,” Elser said. “Our results also suggest that measures to prevent stroke may be especially important in people who have suffered a head injury, which could include interventions like lowering blood pressure and cholesterol, increasing physical activity and smoking cessation.”