Suffering a traumatic brain injury from a blow to the head boosted dementia risk by 24 per cent in a Danish study group of nearly three million people, researchers said Wednesday.
The survey of 36 years' worth of data -- collected from the Danish national patient register -- found that the risk of dementia rose with the number and severity of brain injuries, a team wrote in The Lancet Psychiatry, a medical journal.
"Individuals with a history of traumatic brain injury (TBI)... have an increased risk of developing dementia, even decades after the injury," said study leader Jesse Fann of the University of Washington School of Medicine in Seattle.
This included "less severe" injuries such as concussion.
But the team stressed the absolute risk to any individual remained low. In the study group, 5.3 per cent of dementia sufferers had experienced a brain injury when younger, compared to 4.7 per cent of people without dementia.
"Our findings do not suggest that everyone who suffers a traumatic brain injury will go on to develop dementia later in life," Fann said.
But it would be advisable for people who had suffered a severe knock to the head -- whether in a fall, car accident, through contact sport, or an assault -- to take extra precautions.
This could include regular exercise and avoiding other risk-boosting behaviours such as smoking, or eating and drinking too much.
'Best evidence yet'
"Importantly, a person who has sustained a TBI should do what they can to prevent further TBIs as the risk of dementia increases with the number of TBIs," Fann told AFP.
Previous studies on a link between brain injury and dementia yielded contradictory results.
According to the UN's World Health Organisation, about 50 million people worldwide suffer from dementia, including Alzheimer's Disease -- the most common form with about two-thirds of cases.
There are about 10 million new dementia cases each year.
According to the study authors, more than 50 million people every year experience a traumatic brain injury.
One possible weakness of the study was that it looked at people from a single country with a "fairly similar ethnic population", said the authors -- meaning its findings may not apply to people of other ethnic groups in other countries.
Commenting on the research, University College London neurology professor Jonathan Schott said it provided "perhaps the best evidence yet that traumatic brain injury is a risk factor for dementia."