In absolute terms, 5.3 per cent of participants with dementia had a history of TBI compared with 4.7 per cent of those without the condition.
The study is based on analyzing 36 years of medical records for almost 2.8 million people in Denmark over age 50, looking at their histories of brain injuries, dementia and other medical conditions.
"People who have suffered traumatic brain injury (...) are at an increased risk of developing dementia, even decades after the injury", explains study leader Jesse Fann of the University of Washington School of Medicine in Seattle.
Fann said another important finding is that if you have a brain injury in your 20s, the risk of developing dementia in your 50s is increased by 60 per cent.
Dementia affects 47 million people worldwide and the number of patients is expected to double in the next 20 years.
Every year, over 50 million people worldwide experience a TBI, which occurs when an external force disrupts the brains normal function. Causes include road traffic accidents, falls, sporting accidents and assaults.
The researchers noted that while previous research has suggested a link between TBI, including concussion, and subsequent dementia, earlier studies have been limited in size and details, and have had short follow-up periods. Whether TBI among veterans and in contact sports such as football and boxing increases the risk of dementia has been hotly debated.
Funded by the Lundbeck Foundation, the report closes with a call for increased efforts to prevent TBI and to identify strategies that ameliorate the risk and impact of subsequent dementia.
However researchers in this study took account of other influences on dementia risk, like diabetes, heart disease, depression and substance abuse.
Researchers found that age plays a factor: "the younger younger a person was when sustaining a TBI, the higher the HRs [hazard ratios] for dementia when stratified by time since TBI".
'There are 850,000 people with dementia - this number is set to rise to 1 million by 2021 and more research is urgently needed to fill the gaps in our understanding of lifestyle factors that increase dementia risk'.
This included "less severe" injuries such as concussion.
Researchers at the University of Edinburgh in Scotland developed a new score using information collected with the GSC to determine the condition of a patient's central nervous system in serious trauma or intensive care.
Of the population studied, 132,093 individuals (4·7 percent) had at least one TBI during 1977-2013, and 126,734 (4·5 percent) had incident dementia during 1999-2013.
In the first TBI diagnoses, 85 per cent had been characterised as mild and 15 per cent had been characterised as severe or skull fracture.