More years on the field, non-goalkeeper positions associated with higher risk

Former professional soccer players are at significantly higher risk for developing neurodegenerative disease compared to the general population, researchers from Scotland found—and players in outfield positions and those with longer careers faced the highest risk.

High-impact sports that lead to repeated traumatic brain injury—such as boxing and U.S. football—have a strong association with late-life neurodegenerative diseases, including dementia, motor neuron disease, and Parkinson’s disease. However, less is known about future neurodegenerative risk in sports that have lower incidence rates for TBI, including the most popular participation sport in the world, soccer, William Stewart, MBChB, PhD, of the Department of Neuropathology at Queen Elizabeth University Hospital in Glasgow, U.K., and colleagues explained in JAMA Neurology. While soccer is primarily played using the feet, heading—using one’s head to hit the ball—is also considered an integral part of the game, potentially opening the door for repetitive head injury.

Stewart and colleagues used data from national electronic health records to study the association of soccer field position, professional career length, and era of play with risk of neurodegenerative disease among male former professional soccer players in Scotland.

“In this retrospective cohort study, risk of neurodegenerative disease among a cohort of male former professional soccer players was associated with field position and career length,” they reported. “While overall risk of neurodegenerative disease was around 3.5 times higher in former professional soccer players than in the matched general population control individuals, we found no significant increase in risk of neurodegenerative disease among goalkeepers. In contrast, risk was high across all outfield positions and highest in defenders, who had an approximately 5-fold increase in risk of neurodegenerative disease compared with the matched general population control individuals. Further, risk of neurodegenerative disease among outfield players increased with career length. In contrast, risk of neurodegenerative disease remained similar for former soccer players born between 1910 and 1969.”

In an editorial accompanying the study, Breton M. Asken, PhD, ATC, and Gil D. Rabinovici, MD, associate editor of JAMA Neurology, both of the University of California, San Francisco, noted that the findings by Stewart et al expand on those from the 2019 Football’s Influence on Lifelong Health and Dementia Risk (FIELD) study—also conducted by Stewart and colleagues—which provided the first large-scale epidemiologic evidence that male professional soccer players faced a higher risk for dementia.

That being said, Asken and Rabinovici noted that the public health relevance of these findings will largely depend on the extent to which this risk carries over to amateur and recreational soccer: “As the authors acknowledge, targeted study of nonprofessional soccer participation is necessary to determine whether the precipitous drop in neurodegenerative disease risk observed with fewer years of professional experience continues to decline and perhaps approaches general population risk with fewer overall years of play.”

And, they added, there is “an urgent need to characterize the risk of female soccer players,” given that female participation in the sport is expanding across the globe.

“Overall, the body of evidence linking professional soccer participation with later-life dementia is rapidly growing, revealing an ugly side to the beautiful game,” they concluded. “These data represent an unequivocal call for soccer’s governing bodies to take action to minimize risks for long-term negative health outcomes, implementing rule changes that optimize head trauma prevention while preserving soccer’s rich integrity and international popularity.”

For this analysis, the study authors identified former professional soccer players using the Record of Pre-War Scottish League Players version 2 and the Record of Post-War Scottish League Players version 6—inclusion criteria included individuals 40 years of age or older as of Dec. 31, 2016, male sex identified via electronic health record, and complete birth data.

General population controls were matched 3:1 to former players by year of birth, sex, and area socioeconomic status. The study authors used Scottish Morbidity Record SMR01/SMR04 data sets to ascertain neurodegenerative disease status—including dementia not otherwise specified, Alzheimer disease, non-Alzheimer dementia, motor neuron disease, and Parkinson disease—as well as prescription drug use for dementia.

The study’s primary outcome was incident neurodegenerative disease diagnosis.

The study cohort consisted of 30,704 males, of whom 7,676 were former professional soccer players and 23,028 were matched population controls. The study authors identified 386 former soccer players (5.0%) and 366 matched controls (1.6%) with neurodegenerative disease diagnoses (hazard ratio [HR], 3.66; 95% CI, 2.88-4.65; P<0.001).

“Compared with the risk among general population control individuals, risk of neurodegenerative disease was highest for defenders (HR, 4.98; 95% CI, 3.18-7.79; P<0.001) and lowest for goalkeepers (HR, 1.83; 95% CI, 0.93-3.60; P=0.08),” the study authors wrote. “Regarding career length, risk was highest among former soccer players with professional career lengths longer than 15 years (HR, 5.20; 95% CI, 3.17-8.51; P<0.001). Regarding playing era, risk remained similar for all players born between 1910 and 1969.”

Stewart and colleagues noted that the slightly higher risk for neurodegenerative disease found among goalkeepers did not reach their prespecified cutoff for statistical significance—while they noted that this is likely due to the fact that goalkeepers are less likely to perform headers than outfield players, they also acknowledged that the finding may reflect “insufficient numbers in our data set to power the analysis.”

They also took note of the relatively similar rates of neurodegenerative disease diagnoses across eras of play, explaining that, while the regulation weight for soccer balls has not changed since 1872, the latter half of the 20th century saw a transition from balls made with harder, leather shells to lighter, synthetic shells. While this suggests that the early days of the transition away from leather soccer balls did not lessen the risk for neurodegeneration, Stewart and colleagues also acknowledged that their data “does not permit analysis of outcomes in players participating in an era when the soccer ball was solely synthetic. Further, there have been advances in sports medicine in recent decades, particularly around the assessment and management of symptomatic head injuries. As such, whether risk remains high in soccer players born after 1969 remains unknown.”

Asken and Rabinovici argued that the findings by Stewart et al, among other literature, should sound alarm bells for national and international soccer governing bodies.

Most efforts to minimize head impacts in soccer have been targeted at youth players, they noted, with the U.S. Soccer Federation recently banning headers in practices and games for players younger than 10 years. They also pointed out that some soccer governing bodies recently announced a pilot program that would allow teams to replace up to two players with suspected concussions beyond standard substitution limits.

“These proposed rule changes notwithstanding, professional soccer has been scrutinized for inadequate enforcement of head-safety rules,” they argued. “A recent study estimated that 60% of 90 suspected concussions during the 2018 World Cup tournament were not appropriately managed in accordance with existing protocols. Players evaluated by health care personnel were assessed for a median of less than 1 minute. Clearly, much more rigorous protocols are needed to protect player safety at all levels.”

Stewart and colleagues reached the same conclusion, writing that “adopting a precautionary principle approach to mitigate risk of neurodegenerative disease by reducing exposure to TBI and head impacts in soccer and wider sports might be advised.”

Study limitations included a lack of information on non-professional soccer participation and participation in other contact sports among the study cohort and lack of electronic health record information on other risk factors for neurodegenerative disease.

  1. Former professional soccer players had an increased risk for neurodegenerative diseases compared to age-matched general population controls, with players in outfield positions and those with longer careers facing the highest risk.

  2. Researchers concluded that more rigorous precautions to minimize exposure to traumatic brain injury in soccer and other sports may be advised to reduce risk of future neurodegerative disease.

John McKenna, Associate Editor, BreakingMED™

Stewart reported grants from the Football Association, the Professional Footballers Association, and National Health Service Research Scotland during the conduct of the study, and he is also a nonremunerated member of the Football Association’s Expert Panel on Concussion and Head Injury in Football and of the Fédération Internationale de Football Association (FIFA) Independent Football Concussion Advisory Group. Coauthor Russell reported grants from the Football Association and Professional Footballers Association during the conduct of the study.

Cat ID: 361

Topic ID: 82,361,730,361,138,139,192,48,925