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.

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  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 Martin Burtscher

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