Background: It is often argued that the long-term effects observed in athletes who have experienced multiple mild traumatic brain injuries (mTBI) are due to alcohol rather than the mTBI(s). This systematic review aims to identify and critique the literature to explore whether alcohol use is a modifier in the clinical presentation of chronic traumatic encephalopathy (CTE) and cognitive functioning of athletes with a history of mTBI.

Objectives: This systematic review aimed to investigate the evidence surrounding the potential role of alcohol use on long-term cognitive functioning, neurodegenerative outcomes, and possible increased likelihood of the post-mortem diagnosis of CTE for athletes with a history of TBI. The review intended to create a greater understanding of this evidence through the synthesis and quality appraisal of existing knowledge in literature.

Methods: Systematic searches of CINAHL Complete, MEDLINE and SPORTDiscus, Scopus, Web of Science and PsycINFO databases using keywords related to contact sports, athletes, traumatic brain injury/concussion, neurodegenerative diseases, and alcohol. The database searches were conducted within the months of June to 11th November 2021. The databases searched included literature from the 1970s’ until July 2021. To be included in the review, studies needed to present data on: 1) Sportspeople engaged in at least one competitive season of sport; 2) Alcohol use 3) Include participants with a history of mild traumatic brain injury or repeated head impact sustained from sports participation; and 4) Include at least one neurocognitive or neuropathological outcome. The included studies were appraised using the British Medical Journal Appraisal Tool for Cross-Sectional Studies; containing 20 items surrounding study design, reporting quality, ethical quality and potential conflicts of interest - the latter of which was highlighted for its importance in the review due to its socio-political context.

Results: Five articles (Bieniek et al., 2020;5 Gardner et al., 2017;6 Hume et al., 2016;7 Jordan et al., 19968 and Mathias et al., 20149) met the inclusion criteria. All five studies had no strong evidence for the role of alcohol as a modifier for long-term cognitive difficulties or the likelihood of the post-mortem diagnosis of CTE. One study5 showed higher rates of antemortem alcohol use in cases with CTE. Discussion: Although numerous articles suggested alcohol use as a modifier, a lack of literature in which alcohol use data were linked with neurocognitive and neurodegenerative outcomes for athletes with a history of TBI was identified. Interpretations of such data were seldom reported. Of the five included articles, authors found no differences in measures of depression, anxiety, or cognitive functioning. There was no evidence of alcohol use as a modifier for tauopathy or increased likelihood of CTE for athlete cases, although one study5 found higher rates of antemortem alcohol use in CTE cases.

Conclusion: There was no conclusive evidence from the literature for the potential role of alcohol use in long term cognitive functioning, neurodegenerative outcomes, or possible increased likelihood of the post-mortem diagnosis of CTE for athletes with a history of TBI.