Head injury, sport and the risk of dementia

A group of world-leading researchers reviewed the highest quality research into the link between different factors and dementia risk. They brought together several large population studies on head injuries and concluded that head injuries are one of most important risk factors for dementia.

A study in Denmark showed an increased risk of dementia for 10 years after a head injury in people over the age of 50. They also found the risk of dementia increased with the number of head injuries received.

A study in Sweden showed a similar relationship between brain injury and dementia risk – with the risk increasing with the number and severity of head injuries.

It’s important to remember that observational studies can identify patterns, links and trends. Although they may show an association – that more people with head injuries go on to develop dementia than those without – they cannot tell us whether head injuries were the direct cause of dementia. They do help us to identify key questions that need further exploration.

Several studies looked for early signs of dementia in the brains of people who have experienced traumatic brain injuries. Many years after the injury, they identified the build-up of tau tangles and amyloid plaques (seen in Alzheimer’s disease and other types of dementia) in the brains of people who have experienced a severe brain injury. However, we don’t know if these individuals went on to develop dementia.

A study led by the University of Glasgow, compared the causes of death of over 7,600 professional football players with 23,000 individuals from the general population. They found that professional football players had a three and a half times higher risk of death from progressive brain diseases than the general population.

Within this, they had a five times greater risk of death from Alzheimer’s disease. The study also showed that goalkeepers were less likely to receive prescriptions for dementia drugs than outfield players. This may relate to the lower contact with other players or the reduced heading that goalkeepers do.

Other research into professional rugby players found they have a two times increased risk of developing dementia later on in life.

These studies show the urgent need to accurately gather data relating to traumatic brain injuries (from mild to severe) in sports over time. We also need to learn more about how the number and type of injuries sustained during contact sport change dementia risk. Further research will also help us understand what the underlying mechanism may be.

Currently, there is no data on dementia risk in amateur football. However, changes in the brain associated with chronic traumatic encephalopathy (CTE) has been reported in the brains of amateur football and rugby players.

Chronic traumatic encephalopathy is a form of progressive brain disease. Unlike other dementias, it is directly linked to repeated head injury. While it is known to cause some specific symptoms, it can be confused with other dementias. Therefore, CTE can only be properly diagnosed at autopsy by examining the changes to the brain that it caused.

The phrase ‘punch drunk’ was first used to describe the behavioural changes and thinking problems that occurred in former boxers almost a century ago. These problems are now thought to be symptoms of CTE. Other symptoms include memory loss, changes in mood, confusion and disorientation. It is uniquely associated with a history of brain injury and repetitive head impacts.

Other sports people have also been diagnosed with CTE – including footballers, rugby players, American football players as well as those involved in combat sports. In studies of the brains of former footballers and rugby players that developed dementia, the majority had microscopic changes in their brains associated with CTE.

However, there were also other changes in the brain present that look more like Alzheimer’s disease changes. The final dementia diagnosis in these former athletes can actually be a range of disorders, not just CTE.

An important observation is that CTE changes are in large numbers of former contact sports athletes with dementia. This pathology is uniquely linked to brain injury and head impact exposure, suggesting these are key factors in dementia risk in these former athletes.

It is important to note that only some people who sustain repeated traumatic brain injuries will develop CTE. Others will not and the reasons for this are unclear. Additionally, we do not know how common this disease might be among people with a history of brain injury. Therefore, we need more research to fully understand CTE.

Acknowledgements: With particular thanks to Professor William Stewart, Consultant Neuropathologist at University of Glasgow for his support in developing this resource.