08 Nov 2019

Former professional soccer players are more likely to develop a neurodegenerative disease than the general population, according to a November 7 paper in the New England Journal of Medicine. Researchers led by William Stewart, University of Glasgow, Scotland, U.K., found that while these retirees were less likely to die of lung cancer or ischemic heart disease, they were five times more likely to die with Alzheimer’s, Parkinson’s, or motor neuron disease. The players were also prescribed more dementia medication. “Our findings suggest that although there are benefits of participation in [soccer], with reduced cardiac disease and cancers, there is a considerable increased risk of neurodegenerative disease,” Stewart told Alzforum. The results add to scant epidemiological data on the risk of multiple health outcomes, including neurodegenerative disease, among professional sports players.

Former pro soccer players are less likely to die of heart disease and cancer before 70.

After 70, they are up to five times as likely to die of a neurodegenerative disease.

This group also takes more dementia-related medications.

Sports with a hefty dose of head impacts recently have been associated with chronic traumatic encephalopathy (CTE), a neurodegenerative condition marked by aggregation of tau in the brain (Nov 2012 news). Some years back, researchers started reporting that former professional American football players were three times more likely to die of a neurodegenerative disease than the general population or than baseball players who aren’t exposed to routine head trauma (Lehman et al., 2012; Nyugen et al., 2019). Soccer players must also deal with frequent bumps to the head during games and practice drills. Case reports suggest that they, too, are at increased risk for neurodegenerative diseases, including CTE, though it remains to be seen if that is linked to heading the ball (Feb 2017 news on Ling et al., 2017; Lee et al., 2019). Other studies, led by Martha Shenton, Brigham and Women's Hospital, Boston, report an uptick in neuroinflammatory markers, compromised lower-white-matter integrity, and cortical thinning in soccer players, even those with no history of outright concussions (Koerte et al., 2015; Koerte et al., 2012; Koerte et al., 2015). However, until now no one had done an epidemiological study to evaluate the risk of neurodegenerative disease in professional soccer players.

The literature on CTE (so far) is based on autopsy series, not on a population-based assessment of any group of people, said Michael Lipton, Albert Einstein College of Medicine, New York. “This is new in the sense that they looked at a total cohort of individuals who were exposed in a specific setting to a specific kind of repetitive head trauma.”

First author Daniel Mackay and colleagues examined medical records of 7,676 former professional soccer players from Scotland born before January 1, 1977. They gathered names using databases of all Scottish professional soccer players. With names and birth dates, they could match the majority of players to their unique number in the Community Health Index, a population registry used in Scotland for tracking health care. This number allowed the researchers to access records from the National Prescribing Information System, which documents prescriptions dispensed in the community, and to access death certificates, which contain International Classification of Diseases (ICD) codes for primary and contributing causes of death. They compared these records to those of 23,028 controls from the general population matched for sex, age, and socioeconomic status. The researchers analyzed data through the end of 2016.

By then, 1,180 former soccer players and 3,807 controls had died, or 15.4 and 16.5 percent of each cohort, respectively. Player mortality was lower than for controls up until the age of 70, after which it was higher. Former players were less likely to die of ischemic heart disease or lung cancer, likely the result of increased physical fitness and less smoking, the authors surmised. However, after adjusting for lower mortality to cardiovascular disease and cancer, former players were 3.45 times more likely to have a neurodegenerative disease listed as a cause of death than were controls. Broken down by specific disorder, the risk was highest for Alzheimer’s disease, with a hazard ratio of 5.07, followed by motor neuron disease and Parkinson’s with HRs of 4.33 and 2.15, respectively. The authors noted that that there are no ICD codes for CTE, so they could not evaluate its prevalence. Former players were also five times more likely to have been prescribed a dementia-related medication.

The authors hypothesize that in soccer, the elevated risk of neurodegeneration comes from repetitive impacts to the head. Based on this, they predicted that goalkeepers would be least affected given that they have lower rates of head injury. As it turns out, field position did not affect mortality rates, however, fewer goalies were prescribed dementia-related medications. Stewart suspects a larger sample of goalies would have turned up a difference in mortality as well. Shenton suggested that separating players into those with a history of concussions and those without could reveal greater differences as well. However, she noted that sub-concussive blows to the head can still result in pathological brain changes.

Lipton pointed out that this is a retrospective cohort study, so it doesn’t get into direct causation or specifics about what confers risk. “It is likely that there’s an interaction between head trauma and other things about individuals that confers risk, such as genetic predisposition to dementia,” he suggested.

Where does this leave heading in soccer? “Perhaps, there is adequate evidence that repeated blows to the brain from heading in professional soccer is an occupational risk that needs to be addressed,” wrote Robert Stern, Boston University School of Medicine, in an accompanying NEJM editorial. Still, he doesn’t think amateur players, parents, or coaches should panic, because more research would be needed before generalizing these results to amateur sports. “However, it is also important that the findings from the current study lead to research and increased awareness of the potential short-term and long-term consequences of heading the ball in amateur soccer,” he said.—Gwyneth Dickey Zakaib