Professional soccer players appear to be at considerably increased risk for death from neurodegenerative diseases, including Alzheimer disease (AD), amyotrophic lateral sclerosis (ALS), and Parkinson disease (PD), new research shows.
A retrospective cohort study of more than 7000 former professional soccer players showed that overall, they had a threefold increased risk for death from neurodegenerative disease compared to a matched group of healthy control persons.
Former soccer players had a fivefold increased mortality risk from AD, a fourfold increased risk of dying from motor neuron disease/ALS, and a twofold increased mortality risk from PD.
On the other hand, soccer players had a significantly lower risk of dying from nonneurologic disorders, including heart disease and lung cancer.
“This is first, robust evidence of a considerable increase in neurodegenerative disease mortality in contact sports,” principal investigator Willie Stewart, PhD, Institute of Neuroscience and Psychology, University of Glasgow, Scotland, told.
He added that although specific risk factors cannot be identified in the study, there is sufficient evidence from this study and previous research to support exposure to repetitive mild traumatic brain injury (TBI) and head trauma “as the number one” candidate risk factor.
“As such, across all sports, the aims should be to better recognize and manage TBI and to reduce exposure to head impacts where at all possible,” said Stewart, who is also from the Department of Neuropathology at the Queen Elizabeth University Hospital in Glasgow.
The study was published online November 7 in the New England Journal of Medicine.
Head Trauma and CTE
Stewart noted that there has been growing concern that exposure to repetitive mild TBI and head trauma in sport increases the risk for chronic traumatic encephalopathy (CTE).
“That used to be thought to be almost exclusive to boxers but has now been recognized in autopsy studies on former participants across numerous contact sports, including soccer,” he said.
As reported, CTE is also common among former hockey players and US football players.
Despite recognition of CTE in past neuropathology studies, “only very limited data” exist on risk for neurodegenerative disease in contact sport participants. “And much of that is from studies with various methodological deficiencies,” Stewart said.
The current study “represents the first investigation in any sport to address the multiple limitations of previous research,” he added.
From the Football’s Influence on Lifelong Outcomes and Dementia Risk (FIELD) study, the investigators evaluated mortality data from comprehensive electronic health records of 7676 male former professional soccer players from Scotland who were born between 1900 and 1976. Death records were used to identify 23,028 matched individuals from the general population, who served as the control group.
“These death certification records provide the most complete picture of outcomes in the available datasets,” Stewart noted.
The national Prescribing Information System was mined for prescription information.
A Primary Cause of Death
Results showed that mortality of any type was actually lower for the former soccer players vs the control group ― but only until age 70, when it increased.
Mortality from the following nonneurodegenerative diseases was significantly lower for the full group of former soccer players vs the control group:
- Ischemic heart disease: hazard ratio (HR), 0.80; P = .02;
- Lung cancer: HR, 0.53; P < .001.
Neurodegenerative disease was listed at the primary cause of mortality in 1.7% of the soccer group vs 0.5% of the control group (HR, 4.10; 95% confidence interval [CI], 2.9 – 5.9; P < .001).
After adjusting the HR for risk for death from ischemic heart disease and/or cancer, the subhazard ratio for risk for death from neurodegenerative disease was still 3.5 in soccer players (95% CI, 2.1 – 5.6; P < .001).
In addition, “mortality with neurodegenerative disease listed as the primary or a contributory cause on the death certificate varied according to disease subtype,” the investigators write.
For former players vs the control group, the HRs were 5.07 for mortality from AD (95% CI, 2.9 – 8.8; P < .001), 4.33 from ALS (95% CI, 2.1 – 9.2; P < .001), and 2.15 from PD (95% CI, 1.2 – 4.0; P = .01).
Former soccer players were prescribed dementia-related medications more frequently than control persons (odds ratio, 4.9; 95% CI, 3.8 – 6.3; P < .001).
Interestingly, goalkeepers were prescribed this type of medication less frequently than outfielders (P = .02), but mortality from neurodegenerative disease did not differ between the player subgroups.
The researchers note that the findings now need “to be confirmed in prospective matched-cohort studies.”
Higher Than Predicted
Stewart said that on the basis of available literature, as well as previous research from his team, they had anticipated that the current study would show “some evidence of lifelong health benefits” in former soccer players ― but also a mild to moderate increase in neurodegenerative disease in this group.
“However, the extent of neurodegenerative diseases risk in former soccer players was perhaps at the upper end of our predictions,” he said.
Asked how these rates might compare with those found in American football/National Football League (NFL) players, Stewart said this is not an easy question to answer.
“Although studies in former NFL players have been pursued, data were compared to US population mortality figures rather than appropriately matched controls. As such, these methodological limitations mean direct comparison with our data is not possible,” he said.
“Nonetheless, the reported neurodegenerative mortality in former NFL American football players is similar to what we observed in former professional soccer players,” he added.
Stewart noted that the study did not evaluate young people, so relevance of the study’s data to youth or amateur soccer players is unknown.
“I’d continue to recommend participation in physical activity, including soccer, whilst at the same time making every effort to better recognize and manage concussion and reduce exposure to unnecessary head impacts,” he said.
“That way, if we can achieve this, we will have the potential to retain the health benefits of sport while reducing risk of neurodegenerative disease ― a win-win.”
Occupational Risk?
In an accompanying editorial, Robert A. Stern, PhD, Boston University Chronic Traumatic Encephalopathy Center, Massachusetts, noted that recent research has shown a link between some contact and collision sports and increased risk for later-life neuropsychiatric and cognitive impairment, as well as for CTE.
“It appears that it is not just the ‘big hits’ resulting in symptomatic concussions that increase the risk of neurologic disorders in later life. Rather, the total duration of exposure to repetitive head impacts…has been associated with neuropathology,” Stern writes.
That said, these new study findings “should not engender undue fear and panic among soccer players, parents, and coaches,” he notes.
“As the authors of the current study indicate, it is not possible to generalize their findings…to participants in recreational, amateur, or collegiate-level soccer,” he adds.
More research should be conducted on both short- and long-term consequences from heading a ball by amateur soccer players and female former professional soccer players “in order to confirm or refute” these new data.
“Perhaps, however, there is already adequate evidence that repeated blows to the brain from heading in professional soccer is an occupational risk that needs to be addressed,” Stern writes.
Funder Response
The current study was funded by the Football Association (FA) and the Professional Footballers Association, as well by a National Health Service Research Scotland Career Researcher Fellowship.
The FA released a video of the organization’s chairman in which he was asked whether rule changes are needed.
“Potentially, but not yet,” answered Greg Clarke. He added that “the actual causes of these issues” still need to be identified in further research.
“Globally, the game needs to evolve; we will evolve it. But today, all we need to do is to observe concussion management protocols and limit repetitive heading exercises. They’re the only changes we’re seeking to make,” Clarke said.
Stewart reports no relevant financial relationships. However, he notes that he is an unpaid member of the Football Association’s Head Injury and Concussion Expert Panel. Stern reports having received grants from the NINDS, the NIA, and the Concussion Legacy Foundation and personal fees from Biogen, Eli Lilly, and Psychological Assessment Resources, Inc.
N Engl J Med. Published online October 21, 2019.
