Sport and dementia position statement

Background

The evidence base for dementia risk reduction has made significant advances in recent years. In 2020 the Lancet Commission on Dementia Prevention, Intervention and Care[1] systematically reviewed the current evidence to suggest that globally up to 40% of dementia cases may be prevented or delayed by addressing 12 modifiable risk factors. These risk factors included traumatic brain injury, which researchers suggested may contribute to 3% of dementia cases. However, the risk of head injury must be balanced against the wider benefits of exercise for dementia risk and healthy life expectancy more broadly. The most consistent evidence to date suggests that what is good for heart health is also good for brain health for most of the population[2]. So common risk factors like high blood pressure, smoking, physical inactivity and obesity could have a big impact on dementia rates at a population level. Managing these modifiable risk factors, as well as minimising traumatic brain injury, throughout the life course is important to reduce the risk of developing dementia.

There has been growing interest in the link between head injuries and dementia, from a single more severe traumatic brain injury to repeated sports injuries. Research suggests that people with a traumatic brain injury could be around 50% (1.5 times) more likely to develop dementia[3] than those without. However head injuries can vary enormously, as can the diseases that cause dementia, so the relationship is hard to unravel. We do know that one specific type of dementia is associated with head injury, known as chronic traumatic encephalopathy (CTE)[4]. CTE has been diagnosed in former participants of many sports including American football, baseball, football, ice hockey, rugby and wrestling. As CTE can currently only be diagnosed post-mortem, the actual incidence may be more common than current estimates[5]. However, there is still a limited amount of robust research in this area, and we do not fully understand why the link between head injury and dementia exists or which patients may develop dementia following head injuries.

Existing evidence

Alzheimer’s Research UK collaborated with the Health Policy Partnership (HPP) in 2022 to undertake a landscape review in the field to understand the current evidence base, as part of a project to identify research gaps in the area of sport as it relates to brain health and dementia risk reduction. This is an area where the research evidence is still emerging, and where data is incomplete or relies on self-reporting. This means that current findings are not always clear cut and can be open to a range of interpretations. While further research is clearly needed, it is important that where there is evidence of risk, this is used constructively in relevant sports to minimise risk.

Most existing research in this field has focused on elite male athletes, but other groups may be at different risk of long-term neurological damage. Hundreds of millions of people are actively involved in sports around the world, of whom elite males represent only a small proportion. There are important health benefits from participating in sport which may not confer the same risk as for elite athletes. It is becoming increasingly clear that females and adolescents display different risk, injury and recovery patterns to adult males, and therefore require dedicated research, support and policy interventions in the future. Furthermore, each sport has a unique risk profile that needs to be better understood.

Based on our evidence review (in preparation for peer review publication), we summarise the findings for the three sports with the greatest amount of evidence into the relationship between head injury and long-term neurological impact:

Rugby

Rugby has the highest rate of concussion in comparison with other sports at all levels, and there is growing evidence for the association between rugby-related concussions and associated longer-term cognitive conditions. Male Scottish former international rugby union players are over 2.5 times more likely to develop neurodegenerative disease (which includes diseases that cause dementia, motor neuron disease and Parkinson’s disease) than the general population[6].

Other studies have shown poorer cognitive function for people over 80 years old who had more than three concussions during their rugby career. A study which tested for cognitive impairment found a prevalence of 2-17% among rugby players compared to 3% in a comparison group.

Boxing

Men who have boxed have more than twice the risk of developing Alzheimer-like impairment than those who have never boxed. A history of boxing was associated with developing dementia an estimated 4.8 years earlier, and men in the Caerphilly Prospective Study who had boxed seriously when they were younger were more than twice as likely to display cognitive impairment compared to men with no history of boxing[7].

Different types or styles of boxing may confer different risk due to varying length of rounds and approach. Many studies combine multiple combat or fighting sports and do not break down analysis by discipline or subdiscipline, and so further research into the risk of different types of boxing is required.

Football

A study of former Scottish professional football players found a 3.5 times increased risk of death from neurodegenerative diseases and 4.9 times more frequent prescriptions of dementia medications in comparison with a control group. Studies have found that retired footballers are more likely to have neurodegenerative disease, including Alzheimer’s disease, be prescribed dementia medications, have mild cognitive impairment and have higher mortality from neurodegenerative disease than their non-footballer peers. There have also been several post-mortem diagnoses of CTE in former professional football players.

The evidence gaps

We are committed to improving the understanding of the risk factors associated with dementia with a view to minimising the possibility of developing dementia in the future. Understanding the benefits as well as any risks of sport and their contribution towards the overall risk of dementia is an important aspect of our work. We recognise that there is some promising evidence in these areas and in addition the relationship between sport and dementia is becoming an increasingly prominent public issue.

As part of our work with HPP, ARUK published a summary report in 2022, which identified four key research priorities for progress in this area[8]:

  1. Establishing an international research consortium with research teams and funders from around the world to improve the comparability of studies. Currently, studies are often difficult to compare due to differing research methodologies: a more coordinated research effort would make it easier to draw overarching conclusions.
  2. Developing a varied panel of biomarkers that could help detect and manage both traumatic brain injury and the risk of neurodegeneration. We do not currently have an empirical way of measuring damage in the brain from a traumatic brain injury or the diseases that cause dementia. In the future, biomarkers could enable us to identify each person’s individual risk and track their brain health throughout their life.
  3. Conducting long-term studies that monitor specific populations for several decades and look holistically at the factors that may influence neurodegeneration. Decades may pass between a traumatic brain injury and a dementia diagnosis, whilst studies may only last a few years. Longer-term studies are important to better understand the effects of being physically active, having a traumatic brain injury and developing dementia.
  4. Exploring traumatic brain injury outside of elite sports to understand risks in underrepresented groups such as children, females and people playing grassroots sports. Millions of people around the world participate in sports, yet as mentioned above, much of the existing research has focussed on elite and male athletes.

We urgently need further robust research to understand the long-term implications of concussive and sub-concussive events and how they influence dementia risk as well as evidence outlining the potential benefits of sport to a person’s overall risk of dementia. In order to support research to address these gaps, Alzheimer’s Research UK will be investing £500,000 of research funding as part of its current investment of £5m in dementia prevention research.

In addition to looking at the role of sport in increasing dementia risk, we need more research to understand other risk factors and find ways to reduce dementia prevalence more broadly. There has been an increase in dementia prevention research in recent years, but this still lags far behind many other disease areas. In particular, there is a need for robust evidence on how multi-morbidity and clustering of risk factors affects overall risk development during the life course.

Our position

While researchers continue to make progress in addressing the current evidence gaps, we think it's important for sporting bodies to take steps now to minimise head impacts and reduce the risk of traumatic brain injury for participants in their sports. We believe that sporting bodies are the right organisations to lead on this work because they are well placed to understand the practicalities of how this might be done. Distinction should also be drawn between sports where head injury and concussion are objectives of the sport, such as boxing, and sports such as rugby and football where head injury and concussion occur in the normal course of play but could be avoided, reduced or better managed as a precautionary approach while more evidence is gathered.

This position statement is part of a broader programme of work by Alzheimer’s Research UK to highlight the importance of lifestyle factors in reducing the risk of dementia, advocating for a greater emphasis on brain health in national conversations to enable everyone to take positive steps to look after their brains throughout life[9].

References

[1] Livingston, G. et al. (2020) Dementia prevention, intervention, and care: 2020 report of the Lancet Commission. Lancet, 396: 413-46. DOI: https://doi.org/10.1016/S0140-6736(20)30367-6.

[2] Alzheimer’s Disease International and Prince, P. M., Albanese, P. E., Guerchet, D. M., & Prina, D. M, (2014) World Alzheimer Report 2014 Dementia and Risk Reduction: An Analysis of Protective and Modifiable Factors: https://www.alz.co.uk/research/WorldAlzheimerReport2014.pdf

[3] Li Y, Li Y, Li X, Zhang S, Zhao J, Zhu X, Tian G. Head Injury as a Risk Factor for Dementia and Alzheimer's Disease: A Systematic Review and Meta-Analysis of 32 Observational Studies. PLoS One. 2017 Jan 9;12(1): e0169650. DOI: 10.1371/journal.pone.0169650

[4] Chronic traumatic encephalopathy - NHS (www.nhs.uk)

[5] Alzheimer’s Research UK & The Health Policy Partnership (in preparation) The impact of sports and physical activity on dementia risk

[6] Russell, E. R. et al. (2022) Neurodegenerative disease risk among former international rugby union players. J Neurol Neurosurg Psychiatry., 93(12):1262-1268. DOI: https://doi.org/10.1136/jnnp-2022-329675.

[7] Gallacher J, et al. (2022) Amateur Boxing and Dementia: Cognitive Impairment Within the 35-Year Caerphilly Cohort Study. Clin J Sport Med. 32(3):329-333. DOI: https://doi.org/10.1097/JSM.0000000000000976.

[8] Alzheimer’s Research UK & The Health Policy Partnership (2022) Dementia and sport: research priorities for the future:

Sport-and-dementia-report-Jul-2022.pdf (alzheimersresearchuk.org)

[9] Alzheimer’s Research UK & Royal Society for Public Health (2021) Brain Health: A New Way To Think About Dementia Risk Reduction: ARUK_TBH_PolicyReport_05May21.pdf (alzheimersresearchuk.org)

Last reviewed: December 2022