Even when controlling for other medical and psychiatric conditions associated with dementia, such as depression and hypertension, people with TBI were 1.24 times more likely to develop dementia than people without a brain injury. 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.
"Individuals with a history of TBI, including those with less severe injuries have an increased risk of developing dementia, even decades after the injury".
The researchers reviewed the history of approximately 2.8 million cases in Denmark and found that the overall risk of dementia for those with a history of dementia was 24 percent higher than those without a history of brain injuries, after accounting for other risk factors for the disease. The researchers found that the risk of dementia increased by 33 percent for two or three TBIs, 61 percent for four injuries and 183 percent for five or more injuries. Even a single mild T.B.I. increased the risk by 17 percent.
For the study, the team examined 2.8 million people, and followed-up for 36 years. According to the study authors, more than 50 million people every year experience a traumatic brain injury.
Previous studies have been conflicting, because of small sample sizes and short follow-up periods. Causes include road traffic accidents, falls, sporting accidents and assaults. Between 1999 and 2013, 126,734 people (4.5%) aged 50 or older were diagnosed with dementia.
Among men and women with TBI histories, men had slightly higher rate of developing dementia (30 percent vs. 19 percent).
"However, it's important to emphasize that although the relative risk of dementia is increased after traumatic brain injury, the absolute risk increase is low", Fann noted in a journal news release. Our analysis raises some very important issues, in particular that efforts to prevent TBI, especially in younger people, may be inadequate considering the huge and growing burden of dementia and the prevalence of TBI worldwide. 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.