Objective Systematic review of possible long-term effects of sports-related concussion in retired athletes.
Data sources Ten electronic databases.
Study selection Original research; incidence, risk factors or causation related to long-term mental health or neurological problems; individuals who have suffered a concussion; retired athletes as the subjects and possible long-term sequelae defined as >10 years after the injury.
Data extraction Study population, exposure/outcome measures, clinical data, neurological examination findings, cognitive assessment, neuroimaging findings and neuropathology results. Risk of bias and level of evidence were evaluated by two authors.
Results Following review of 3819 studies, 47 met inclusion criteria. Some former athletes have depression and cognitive deficits later in life, and there is an association between these deficits and multiple prior concussions. Former athletes are not at increased risk for death by suicide (two studies). Former high school American football players do not appear to be at increased risk for later life neurodegenerative diseases (two studies). Some retired professional American football players may be at increased risk for diminishment in cognitive functioning or mild cognitive impairment (several studies), and neurodegenerative diseases (one study). Neuroimaging studies show modest evidence of macrostructural, microstructural, functional and neurochemical changes in some athletes.
Conclusion Multiple concussions appear to be a risk factor for cognitive impairment and mental health problems in some individuals. More research is needed to better understand the prevalence of chronic traumatic encephalopathy and other neurological conditions and diseases, and the extent to which they are related to concussions and/or repetitive neurotrauma sustained in sports.
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Competing interests GTM has been reimbursed by the government,professional scientific bodies and commercial organisations for discussing orpresenting research relating to mild TBI at meetings, scientific conferencesand symposiums. He serves as an Unaffiliated Neurotrauma Consultant for theNational Football League. He has received funding from General ElectricCompany, acting through its GE Healthymagination unit. He is also a subcontractPI on The NCAA-DOD Grand Alliance-Concussion Assessment, Research and Education(CARE Consortium). AG has a clinical practice in neuropsychology involvingindividuals who have sustained sport-related concussion (including current andformer athletes). He has operated as a contracted concussion consultant to theAustralian Rugby Union(ARU) from July 2016. He has received travel funding fromthe Australian Football League (AFL) to present at the Concussion in FootballConference in 2013. Previous grant funding includes the NSW Sporting InjuriesCommittee, the Brain Foundation (Australia), and the Hunter Medical ResearchInstitute (HMRI), supported by Jennie Thomas. He is currently funded throughthe HMRI, supported by Anne Greaves, and the University of Newcastle’s PriorityResearch Centre for Stroke and Brain Injury. KS is a physiotherapy consultantat Evidence Sport and Spinal Therapy in Calgary, Alberta, Canada. She hasreceived research grant support through the University of Calgary from theAlberta Children’s Hospital Research Institute, Hotchkiss Brain Institute andthe Canada Foundation for Innovation (including matching funds through theProvince of Alberta). She is a faculty member at the Sport Injury PreventionResearch Centre, which is one of the International Research Centres forPrevention of Injury and Protection of Athlete Health supported by theInternational Olympic Committee (IOC). KMG serves on the NCAA ConcussionProtocol Subcommittee as the Atlantic Coast Conference representative. He isalso a member of the USA Soccer Concussion Committee. JB supervises a TBIresearch laboratory which has received grant funding from pharmaceutical andindustry sponsors and the National Institutes of Health. He has receivedconsulting fees from industry and royalties from intracranial surgeryinstrumentation and has been a consultant for AIBA, NCAA, as well as providingexpert witness testimony for legal cases and the NCAA, and received speaker’shonoraria. He is the chairman of the Medical Advisory Board of Pop WarnerFootball, which is a non-compensated position. RCC serves as aconsultant/advisor to the National Football League Head, Neck and SpineCommittee and National Operating Committee on Standards for Athletic Equipment.He is Medical Director of Concussion Legacy Foundation and receives royaltiesfrom Houghton Mifflin. RC has a clinical and consulting practice in forensicneuropathology, including postmortem neuropathological interpretation ofindividuals who have sustained various types of traumatic brain injury. Hereceives salary support from the Lieber Institute for Brain Development, andsubcontracts with the NIH Neurobiobank at the University of Maryland forneuropathology interpretation. MT has been reimbursed for his travel andaccommodation expenses by conference and seminar organisers internationallywhen invited to speak on concussion and concussion-related topics. In situationswhere the organisers have been unable to provide financial support, theInternational Concussion and Head Injury Research Foundation (ICHIRF) hasreimbursed the cost of his travel and accommodation for attendance at theseevents. He is Medical Director of ICHIRF which receives research funding fromGodolphin Racing, the Injured Jockeys Fund, the NFL and private sponsors. Hedoes not receive any salary from ICHIRF, apart from the expenses mentionedabove. BDJ acts as an Unaffiliated Neurotrauma Consultant for theNational Football League, serves on the NFL Players Association Health andSafety Committee and is a Medical Advisory Physician for NFL Player Benefits. CRhas been reimbursed by professional scientific organisations and commercialentities for presenting research findings on sport-related concussion and mildtraumatic brain injury. He has had a clinical and consulting practice inneuropsychology including forensic neuropsychology, closed to new cases in July2016. He has received no salary support, or any other type of support, for hisresearch on sport-related concussion or brain injury in general. GI has beenreimbursed by the government, professional scientific bodies and commercialorganisations for discussing or presenting research relating to mild TBI andsport-related concussion at meetings, scientific conferences and symposiums. Hehas a clinical and consulting practice in forensic neuropsychology involvingindividuals who have sustained mild TBIs (including professional athletes). Hehas been a principal investigator and co-investigator on federal and industrygrants on topics relating to mild traumatic brain injury, neuropsychologicalassessment and depression. He has received consulting fees from pharmaceuticalcompanies. He receives royalties for books and one neuropsychological test. Hehas received research funding from several test publishing companies, includingImPACT Applications, CNS Vital Signs and Psychological Assessment Resources (PAR).He acknowledges unrestricted philanthropic support from the Mooney-ReedCharitable Foundation and ImPACT Applications. He previously served as acontractor in the area of TBI research through General Dynamics for the Defenseand Veterans Brain Injury Center within the US Department of Defense. Hereceives salary support for chairing the Brain and Behavior committee for theHarvard Integrated Program to Protect and Improve the Health of NFLPA Members.
Provenance and peer review Not commissioned; externally peer reviewed.
Author note The authors thank Amy J Markowitz, JD and Brian Fabian, MPA for editorial support.
Correction notice This paper has been amended since it was published Online First. Owing to a scripting error, some of the publisher names in the references were replaced with 'BMJ Publishing Group'. This only affected the full text version, not the PDF. We have since corrected these errors and the correct publishers have been inserted into the references.