These risks include having another brain injury, being assaulted and suicide. The risks are even higher for those with a psychiatric or drug abuse problem, the researchers added.
"After a traumatic brain injury, patients have a threefold increased risk of dying prematurely," said lead researcher Dr. Seena Fazel, a Wellcome Trust senior research fellow in clinical science at the University of Oxford in England.
"Fifty percent of the early deaths are due to either accident or suicide or being assaulted," he said. "That seems to be related to psychiatric illness and substance abuse."
The study found that 61 percent of these patients had psychiatric or substance abuse problems, Fazel said. In some cases, these problems were present before the injury, while some developed after the injury, he added.
The dangers of developing psychiatric or drug abuse problems after an injury may be caused by a variety of factors, including biological and social changes.
These risks might be a particular problem for soldiers and athletes who have had a traumatic brain injury, Fazel suggested.
"A large number of vets have suffered traumatic brain injuries, and we know a lot of vets are dying from suicide. Traumatic brain injury may be one of the factors that increases their risk," he said.
Fazel believes that after a traumatic brain injury, patients need to be monitored for risk factors that may put them at risk for dying prematurely.
"Some of these problems, like psychiatric illness and substance abuse, can be treated," he said.
While the study found an association between traumatic brain injury and early death, it did not establish a cause-and-effect relationship.
The report was published online Jan. 15 in JAMA Psychiatry.
One expert said he thinks certain personality traits play a part in the phenomenon.
"The people that are dying earlier have personality characteristics that make them vulnerable to have brain injury," said Dr. Robert Robinson, a professor of psychiatry at the University of Iowa and author of an accompanying editorial.
"These people are being injured because they're impulsive and thrill-seeking. These vulnerable personality characteristics are getting them not only into their first head injury, but into a subsequent head injury and that's causing this premature death," he said.
Another expert agreed.
"It makes sense that people who suffer a brain injury are more likely to repeat behavior over time, and have more injuries and be at risk for premature death," said Dr. Jamie Ullman, director of neurotrauma at North Shore University Hospital in Manhasset, N.Y.
"A lot has to do with behaviors that would get them involved in injuries in the first place. We need to focus on the underlying behaviors that have resulted in these injuries, and see if these behaviors can be modified after the injury," she said.
While risky behavior can put people at risk for brain injury and premature death, suicide and depression after a brain injury are also concerns.
Dr. Robert Glatter, director of sports medicine and traumatic brain injury at Lenox Hill Hospital in New York City, said, "Suicide and depression are important issues in patients after a traumatic brain injury."
These patients need a support network after a traumatic brain injury "to make sure they are not falling into depression," he said.
For the study, Fazel's team collected data on more than 218,000 people born in Sweden in 1954 or after and who had suffered a traumatic brain injury between 1969 and 2009.
Among these patients, more than 11,000 died prematurely after their brain injury. Of those who died, 21.5 percent died six months or later after the injury.
The researchers compared the death rates of those with brain injury with more than 2 million people who hadn't had a brain injury and also with more than 150,000 siblings of those who had a brain injury.
The investigators found there was an increased risk of dying prematurely among patients who survived six months after a brain injury compared with those who didn't have a brain injury. The increased risk for dying remained the same for at least five years after the injury, they noted.
These patients were also at risk of early death if they had psychiatric conditions or were substance abusers, the study found.
Visit the U.S. National Institute of Neurological Disorders and Stroke for more on traumatic brain injuries.