In the largest study of its kind, researchers have found that traumatic brain injury is associated with an increased risk of dementia.
Today, a study that analyzed data from 2-point-8 million people found that T-B-Is and their severity heighten the risk of developing dementia.
A single traumatic brain injury characterized as severe increases the risk by 35 percent, while a mild traumatic brain injury or concussion increased the risk by 17 percent.
Dr Carol Routledge, director of research at Alzheimer's Research UK, said: "This well-conducted study adds significant weight to previous evidence of a link between head injury and an increased risk of dementia". 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".
Each year, more than 50 million people worldwide suffer a traumatic brain injury, which occurs when a bump or blow to the head disrupts normal brain function. They assessed the long-term risk of dementia in people who had suffered a TBI, compared to those without a TBI, and also those who had experienced physical traumas that did not involve the brain or spine, such as fractured bones. Among first TBI diagnoses, 85 percent had been characterized as mild and 15 percent had been characterized as severe or skull fracture.
In total, 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 findings also show that men with a history of TBI had a slightly higher risk of developing dementia than women. For example, a person who sustained a TBI in their 20s was 63% more likely to develop dementia 30 years later compared to someone who did not sustain such an injury in their 20s.
Fann said more research is needed to understand who is at greatest risk of dementia and what other factors contribute to that risk.
Despite the size of the studies, they won't settle scientific questions - or social debate - about brain injuries from sports, war, auto crashes or domestic violence.
"Our analysis raises some very important issues, in particular that efforts to prevent traumatic brain injury, especially in younger people, may be inadequate considering the huge and growing burden of dementia and the prevalence of TBI worldwide", Fann said. Five or more brain injuries, the risk is almost 3 times the risk compared to someone without a brain injury. "The association of TBI with different causes and how these change across time needs policy attention, as it is likely that prevention needs to be considered at societal, community, and local levels".