The landmark, University of Glasgow-led research into lifelong health outcomes in former professional footballers, the FIELD study, has revealed further major insights into the link between football and risk of dementia.
In findings published today in the journal JAMA Neurology, researchers report that risk of neurodegenerative disease in former professional footballers varies by player position and career length, but not by playing era.
These results add to the ground-breaking observations from the 2019 FIELD study publication, which found that former professional footballers had an approximately three-and-a-half-fold higher rate of death due to neurodegenerative disease than expected.
Led by consultant neuropathologist Professor Willie Stewart, Honorary Professor at the University of Glasgow, the researchers looked at health records data for around 8,000 Scottish former professional footballers and 23,000 matched general population controls and explored whether risk of neurodegenerative disease varied by player position, length of career or playing era.
The results show that, for goalkeepers, neurodegenerative disease risk was similar to general population levels. In contrast, neurodegenerative disease risk for outfield players was almost 4 times higher than expected and varied by player position with risk highest among defenders, at around 5-fold higher than expected.
These new findings also show that neurodegenerative disease diagnoses increased with increasing career length, ranging from an approximately doubling of risk in those with shortest careers, to around a 5-fold increase in those with the longest careers.
However, despite changes in football technology and head injury management over the decades, there is no evidence neurodegenerative disease risk changed for the population of footballers included in this study, whose careers spanned from around 1930 to the late 1990s.
Prof Willie Stewart said: "We have already established that former professional footballers are at a much greater risk of death from dementia and other neurodegenerative disorders than expected. These latest data from FIELD take that observation further and suggest this risk reflects cumulative exposure to factors associated with outfield positions."
In parallel work led by Prof Stewart, a specific pathology linked to brain injury exposure, known as chronic traumatic encephalopathy (CTE), has been described in a high proportion of the brains of former contact sport athletes, including former amateur and professional footballers.
Prof Stewart added: "Taking these new results together with our and others post-mortem findings and data from our previous FIELD studies, the evidence is clear that the standout risk factor for neurodegenerative disease in football is exposure to head injury and head impacts. As such, a precautionary principle approach should be adopted to reduce, if not eliminate exposure to unnecessary head impacts and better manage head injuries in football and other sports."
Charlotte Cowie, FA Chief Medical Officer, said: "The FIELD study team, funded by ourselves and the PFA, have continued to produce insightful data that has enabled us to make changes in the game. We welcome these new findings."
PFA Chief Executive, Maheta Molango, said: "The PFA would like to thank the FIELD study team. The welfare of our players, past, present and future is at the forefront of everything we do and this data will inform us how best to protect them and improve our services."
FIELD is the largest study to date looking in this detail at the risk of neurodegenerative disease in any sport, not just professional footballer players. The study compared health records of 7,676 former Scottish male professional football players who were born between 1900 and 1976 against those of more than 23,000 matched individuals from the general population. Neurodegenerative disease risk among former football players relative to matched controls was then calculated for a range of player positions and career lengths and for decade of birth.
The study, ’Association of field position and career length with neurodegenerative disease risk in former professional soccer players,’ is published in JAMA Neurology.