People who have had a traumatic brain injury, often called TBI or a serious head injury, do have a higher risk of developing dementia later in life compared with people who never had such an injury.[1][3][4]
Traumatic brain injury happens when a blow, jolt, or hit to the head disrupts how the brain normally works. This can range from a mild concussion to a severe injury that causes bleeding or loss of consciousness. Car crashes, falls, assaults, or contact sports like rugby, boxing, American football, or heading the ball in soccer can all cause TBI.[1][4]
Large research studies have followed people over time and compared those with a history of TBI to those without. Overall, these studies show that dementia is more common in people who have had a TBI.[1][3] According to Alzheimer’s Research UK, research suggests that people with a traumatic brain injury are about 50 percent more likely to develop dementia than those who have not had one.[1] Their position statement on sport and dementia explains that TBI is now recognized as one of several important risk factors that can contribute to dementia worldwide.[1]
The Lancet Commission on Dementia Prevention, Intervention and Care has also highlighted traumatic brain injury as one of the “modifiable risk factors” for dementia. This means it is a factor we may be able to reduce or prevent, unlike age or genetics.[1] The Commission estimates that TBI accounts for roughly 3 percent of dementia cases worldwide, which is a small share overall but still represents many people when you consider global numbers.[1]
Not everyone who has a head injury will get dementia. The risk is higher at a population level, but for any one person it depends on several things. Research suggests that the severity of the injury, the number of injuries across a lifetime, and the age at which they occur all seem to matter.[1][3][4] Severe TBIs and repeated injuries, such as those sometimes seen in contact sports or military service, appear to carry more long term risk than a single mild concussion.[1][3]
Some former athletes with a history of many blows to the head have been found, after death, to have a particular pattern of brain damage called chronic traumatic encephalopathy, or CTE.[1] This is a rare form of dementia that has been described in some boxers, American football players, and other contact sport athletes.[1] Studies of American football suggest that each additional year of play may raise the risk of CTE, although researchers point out that the overall evidence is still limited and we do not yet fully understand who is most vulnerable or why.[1]
Scientists are working to understand how an injury to the brain might raise the chances of dementia. New research suggests several possible processes.[2][3][4] After a TBI, there can be inflammation, damage to blood vessels in the brain, and changes in how waste products are cleared from brain tissue. An article from News Medical describes recent work showing that TBI may disrupt so called brain drainage systems that help wash away abnormal proteins, such as the amyloid and tau proteins involved in Alzheimer’s disease.[4] When these clearance systems do not work well, harmful proteins may build up faster and trigger neurodegenerative diseases like Alzheimer’s and related dementias.[4]
Genetics may also affect who is most at risk. A review in the journal of traumatic brain injury outcomes noted that people who carry certain genetic variants, such as the APOE ε4 gene, might have more persistent problems after mild head injury, including trouble with thinking and memory.[2] This review, available on PubMed Central, suggests that genes related to how the brain repairs itself and handles inflammation may partly explain why some people recover fully while others have longer lasting difficulties.[2] However, the authors also stress that existing studies are small and can be biased, so larger and better designed research is needed before we use genetics routinely to predict outcomes after TBI.[2]
A recent study of older adults, published by researchers at Duke University, looked at how lifetime history of TBI is related to thinking skills in later life.[3] Their work found that people who reported past TBIs tended to have lower scores on cognitive tests and were more likely to develop dementia over time compared with those without such a history.[3] The authors pointed out that TBI might interact with other health problems too, such as high blood pressure, diabetes, or depression, to influence someone’s overall brain health.[3]
It is also important to understand that TBI is just one of many risk factors for dementia. The Lancet Commission lists multiple other contributors, including high blood pressure, obesity, smoking, heavy alcohol use, physical inactivity, hearing loss, social isolation, and low levels of education.[1] Alzheimer’s Research UK notes that by tackling several of these risks together, including preventing or minimizing TBI, we might significantly reduce dementia cases worldwide.[1] In their sport and dementia statement, they estimate that changing these 14 modifiable risks could help prevent or delay up to 45 percent of dementia cases overall.[1]
Because TBI is a risk factor we can sometimes act on, many experts see prevention as a key strategy. For everyday life, this includes things like using seatbelts, installing grab bars and improving lighting to reduce falls, using helmets for cycling or motorbikes, and making workplaces safer.[1][4] In sports, Alzheimer’s Research UK recommends practical steps such as limiting high impact contact and heading in training, ensuring that players return to play gradually and only when fully recovered, and improving protective equipment where appropriate.[1] These measures aim to keep the brain safe without removing the many physical and social benefits of sport.[1]
For people who have already had a TBI, it is still possible to lower overall dementia risk by focusing on brain healthy habits. Experts generally encourage staying physically active, not smoking, limiting alcohol, keeping blood pressure, cholesterol, and diabetes under good control, and staying mentally and socially engaged.[1][3][4] While these steps cannot undo an injury, they may help support the brain and reduce the impact of other risk factors that could add to the burden on brain cells over time.
Doctors and researchers also stress the importance of follow up after any significant head injury. Even mild concussions should be taken seriously if symptoms such as headaches, confusion, memory problems, mood changes, or sleep difficulties persist.[2][3][4] Early assessment and rehabilitation can help manage problems before they become long lasting. In older adults in particular, a fall with a head injury should prompt careful medical review, both to treat the injury and to look for any underlying issues that may increase fall risk, such as vision problems, medication side effects, or balance disorders.[3][4]
While we now have strong evidence that dementia is more common in people who have had a traumatic brain injury, many questions remain. Researchers are still working out how the timing, severity, and number of injuries across a lifetime interact with a person’s genes, lifestyle, and other medical conditions.[2][3][4] New imaging techniques and laboratory methods are giving better insight into the subtle changes that occur in the brain after TBI, from tiny vessel damage to disruptions in waste clearance pathways.[4] These advances may eventually lead to targeted treatments that can be given soon after an
