A study conducted by British and Swedish researchers recently published in JAMA Psychology found that survivors of traumatic brain injuries are three times as likely to die prematurely than those who never experienced the condition.

During a period of four decades, 218,300 Swedes born after 1953 and who experienced a moderate to severe TBI between 1969 and 2009 and didn’t die within six months were observed. Injuries examined included skull fractures, internal bleeding, and loss of consciousness exceeding one hour. Concussions – a lower level TBI – were not monitored as extensively.

During the time researchers tracked the patients, 1.1 percent of the total died before the age of 56. While this isn’t a significantly large percentage, it was three times the rate as the control group (2.2 million individuals without TBIs, including siblings).

Out of the total who died, 574 deaths resulted from accidents, and 522 from suicides. For these specific types of injuries, deaths from accidents were four times the rate of the control group, and double for suicide.

However, the report points out that other factors that may correlate a TBI more closely with death: Those who experienced a brain injury tend to be risk-takers in the first place, and have a greater chance of having a psychiatric disorder or substance abuse problem.

According to the CDC, 1.4 million people per year experience a traumatic brain injury of some kind. The condition, which is classified as an open or closed head injury, may stem from an incident as seemingly minor as a fall or as serious as an IED explosion.

Out of both types of TBIs, closed head injuries tend to be the least obvious, with symptoms showing up months later. For this injury, the brain moves around inside the skull, hitting the bone in the process. Rarely are there any outside signs.

For both types of TBIs, the injured experiences a wide range of symptoms, some immediate and others surfacing later: a change in personality, diminished social and metal skills, inability to make decisions, loss of bodily control, and reduced motor skills.