Older Retired Soccer Players Prone to Neurodegeneration

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

Comments

  1. This is a very interesting study showing that mortality from neurodegenerative diseases, particularly dementia, was higher among former professional soccer players than among controls from the Scottish population. Data based on death certificates and also on documents of prescribed dementia-related medications showed that dementia was more frequent in former professional soccer players than in controls.

    This is probably the first paper that used an epidemiological method to evaluate whether the prevalence of dementia among former professional soccer players is higher than in controls.

    Despite the fact that death certificates are usually not very reliable for epidemiological studies, the frequency of all types of dementia was 0.8 percent in controls and 2.3 percent in former professional soccer players, whereas the mean age at death was 64.7 ± 14.0 years and 67.9 ± 13.0 years, respectively. As the prevalence of dementia for men in Europe is 0.2 percent for individuals aged 60–64 years and 1.8 percent for those 65–69 years, the death certificates of this study were able to recollect a considerable number of cases with the diagnosis of dementia, and were also able to show higher prevalence of dementia in former professional soccer players when compared with the general population (Prevalence of dementia in Europe).

    However, we need to be careful and not to jump to conclusions:

    1. As the authors stressed, these data were obtained for professional soccer players and should not be applied directly to amateur soccer players.
    1. Traumatic brain injury is probably the main factor responsible for the higher frequency of neurodegenerative diseases in former professional soccer players. Dementia was less frequent in goalkeepers than in outfield players in this study, a finding that reinforces that assumption.
    2. The hypothesis that heading is the main cause of traumatic brain injury in soccer needs to be analyzed more carefully. Traumas to the head are among the most frequent in soccer, particularly head to head and elbow to head contacts (Nitrini, 2017; Junge and Dvořák, 2015).
    3. Chronic traumatic encephalopathy may be or may not be the main cause of dementia in former professional soccer players. This study did not evaluate this hypothesis, because the diagnosis of chronic traumatic encephalopathy is based on a clinicopathological evaluation.

    And finally, as also stressed by the authors, “these data need to be confirmed by prospective matched-cohort studies.”

    References:

    Nitrini R. Soccer (Football Association) and chronic traumatic encephalopathy: A short review and recommendation. Dement Neuropsychol. 2017 Jul-Sep;11(3):218-220. PubMed.

    Junge A, Dvořák J. Football injuries during the 2014 FIFA World Cup. Br J Sports Med. 2015 May;49(9):599-602. PubMed.

    View all comments by Ricardo Nitrini

  2. Mackay and colleagues demonstrate increased neurodegeneration-related parameters in a Scottish cohort of former professional soccer players. All-cause mortality up to an age of 70 was reduced in this cohort, but increased thereafter and was associated with an elevated risk of dying from neurodegeneration.

    The study confirms beneficial effects of physical activity on general mortality (Burtscher and Burtscher, 2019), but highlights the importance of consider particulars of different kinds of sport: contact sports especially might increase vulnerability for specific diseases, such as neurodegenerative diseases.

    Given the increasingly recognized importance of lifestyle factors in dementia prevention (Livingston et al., 2017), the matching method for controls Mackay and colleagues used, i.e., the Scottish Index of Multiple Deprivation, 2016, ref. 3, represents an interesting approach whose validity has to be confirmed. According to the cognitive reserve concept (Stern, 2012), lifestyle factors and beneficial social environments (such as partially assessed in SIMD), including education and social interactions, can confer resilience against brain pathology.

    Assuming that former professional soccer players constitute a unique socioeconomic group, a comparison to the overall Scottish population SIMD distribution would have been interesting and could help to assess potential confounding related to socioeconomic status and cognitive reserve development opportunities. In this context, the suitability of matching subjects according to the SIMD as performed by Mackay and colleagues needs further validation, because the SIMD informs about the neighborhood, i.e. data zones, not individuals (SIMD).

    References:

    Burtscher J, Burtscher M. Run for your life: tweaking the weekly physical activity volume for longevity. Br J Sports Med. 2019 Oct 19; PubMed.

    Livingston G, Sommerlad A, Orgeta V, Costafreda SG, Huntley J, Ames D, Ballard C, Banerjee S, Burns A, Cohen-Mansfield J, Cooper C, Fox N, Gitlin LN, Howard R, Kales HC, Larson EB, Ritchie K, Rockwood K, Sampson EL, Samus Q, Schneider LS, Selbæk G, Teri L, Mukadam N. Dementia prevention, intervention, and care. Lancet. 2017 Jul 19; PubMed.

    Stern Y. Cognitive reserve in ageing and Alzheimer's disease. Lancet Neurol. 2012 Nov;11(11):1006-12. PubMed.

    View all comments by Johannes Burtscher View all comments by Martin Burtscher

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References

News Citations

  1. Meet the New Progressive Tauopathy: CTE in Athletes, Soldiers
  2. Do 'Headers' Rack Up Brain Damage in Soccer Players?

Paper Citations

  1. Lehman EJ, Hein MJ, Baron SL, Gersic CM. Neurodegenerative causes of death among retired National Football League players. Neurology. 2012 Nov 6;79(19):1970-4. PubMed.
  2. Nguyen VT, Zafonte RD, Chen JT, Kponee-Shovein KZ, Paganoni S, Pascual-Leone A, Speizer FE, Baggish AL, Taylor HA Jr, Nadler LM, Courtney TK, Connor A, Weisskopf MG. Mortality Among Professional American-Style Football Players and Professional American Baseball Players. JAMA Netw Open. 2019 May 3;2(5):e194223. PubMed.
  3. Ling H, Morris HR, Neal JW, Lees AJ, Hardy J, Holton JL, Revesz T, Williams DD. Mixed pathologies including chronic traumatic encephalopathy account for dementia in retired association football (soccer) players. Acta Neuropathol. 2017 Mar;133(3):337-352. Epub 2017 Feb 15 PubMed.
  4. Lee EB, Kinch K, Johnson VE, Trojanowski JQ, Smith DH, Stewart W. Chronic traumatic encephalopathy is a common co-morbidity, but less frequent primary dementia in former soccer and rugby players. Acta Neuropathol. 2019 Sep;138(3):389-399. Epub 2019 Jun 1 PubMed.
  5. Koerte IK, Lin AP, Muehlmann M, Merugumala S, Liao H, Starr T, Kaufmann D, Mayinger M, Steffinger D, Fisch B, Karch S, Heinen F, Ertl-Wagner B, Reiser M, Stern RA, Zafonte R, Shenton ME. Altered Neurochemistry in Former Professional Soccer Players without a History of Concussion. J Neurotrauma. 2015 Sep 1;32(17):1287-93. Epub 2015 May 14 PubMed.
  6. Koerte IK, Ertl-Wagner B, Reiser M, Zafonte R, Shenton ME. White matter integrity in the brains of professional soccer players without a symptomatic concussion. JAMA. 2012 Nov 14;308(18):1859-61. PubMed.
  7. Koerte IK, Mayinger M, Muehlmann M, Kaufmann D, Lin AP, Steffinger D, Fisch B, Rauchmann BS, Immler S, Karch S, Heinen FR, Ertl-Wagner B, Reiser M, Stern RA, Zafonte R, Shenton ME. Cortical thinning in former professional soccer players. Brain Imaging Behav. 2015 Aug 19; PubMed.

Further Reading

Papers

  1. Koerte IK, Ertl-Wagner B, Reiser M, Zafonte R, Shenton ME. White matter integrity in the brains of professional soccer players without a symptomatic concussion. JAMA. 2012 Nov 14;308(18):1859-61. PubMed.
  2. Zuckerman SL, Brett BL, Jeckell A, Yengo-Kahn AM, Solomon GS. Chronic Traumatic Encephalopathy and Neurodegeneration in Contact Sports and American Football. J Alzheimers Dis. 2018;66(1):37-55. PubMed.
  3. Gardner RC, Yaffe K. Epidemiology of mild traumatic brain injury and neurodegenerative disease. Mol Cell Neurosci. 2015 May;66(Pt B):75-80. Epub 2015 Mar 5 PubMed.

Primary Papers

  1. Mackay DF, Russell ER, Stewart K, MacLean JA, Pell JP, Stewart W. Neurodegenerative Disease Mortality among Former Professional Soccer Players. N Engl J Med. 2019 Nov 7;381(19):1801-1808. Epub 2019 Oct 21 PubMed.
  2. Stern RA. Soccer and Mortality - Good News and Bad News. N Engl J Med. 2019 Nov 7;381(19):1862-1863. Epub 2019 Oct 21 PubMed.

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