*Result*: Neurodegenerative Diseases in Male Former First-Class New Zealand Rugby Players.
Original Publication: [Auckland, N.Z. ; Newtown, PA] : ADIS
Prien A, Grafe A, Rössler R, Junge A, Verhagen E. Epidemiology of head injuries focusing on concussions in team contact sports: a systematic review. Sports Med. 2018;48:953–69. (PMID: 2934965110.1007/s40279-017-0854-4)
Gardner RC, Burke JF, Nettiksimmons J, Kaup A, Barnes DE, Yaffe K. Dementia risk after traumatic brain injury vs nonbrain trauma: the role of age and severity. JAMA Neurol. 2014;71:1490–7. (PMID: 25347255431855810.1001/jamaneurol.2014.2668)
Godbolt AK, Cancelliere C, Hincapié CA, Marras C, Boyle E, Kristman VL, et al. Systematic review of the risk of dementia and chronic cognitive impairment after mild traumatic brain injury: results of the International Collaboration on Mild Traumatic Brain Injury Prognosis. Arch Phys Med Rehabil. 2014;95:S245–56. (PMID: 2458191010.1016/j.apmr.2013.06.036)
McKee AC, Cantu RC, Nowinski CJ, Hedley-Whyte ET, Gavett BE, Budson AE, et al. Chronic traumatic encephalopathy in athletes: progressive tauopathy after repetitive head injury. J Neuropathol Exp Neurol. 2009;68:709–35. (PMID: 19535999294523410.1097/NEN.0b013e3181a9d503)
Asken BM, Sullan MJ, DeKosky ST, Jaffee MS, Bauer RM. Research gaps and controversies in chronic traumatic encephalopathy: a review. JAMA Neurol. 2017;74:1255–62. (PMID: 2897524010.1001/jamaneurol.2017.2396)
Smith DH, Johnson VE, Trojanowski JQ, Stewart W. Chronic traumatic encephalopathy—confusion and controversies. Nat Rev Neurol. 2019;15:179–83. (PMID: 30664683653278110.1038/s41582-018-0114-8)
LeClair J, Weuve J, Fox MP, Mez J, Alosco ML, Nowinski C, et al. Relationship between level of American football playing and diagnosis of chronic traumatic encephalopathy in a selection bias analysis. Am J Epidemiol. 2022;191:1429–43. (PMID: 35434739998935810.1093/aje/kwac075)
Batty GD, Frank P, Kujala UM, Sarna SJ, Valencia-Hernández CA, Kaprio J. Dementia in former amateur and professional contact sports participants: population-based cohort study, systematic review, and meta-analysis. eClin Med. 2023;61: 102056.
Iverson GL, Castellani RJ, Cassidy JD, Schneider GM, Schneider KJ, Echemendia RJ, et al. Examining later-in-life health risks associated with sport-related concussion and repetitive head impacts: a systematic review of case-control and cohort studies. Br J Sports Med. 2023;57:810–24. (PMID: 3731618710.1136/bjsports-2023-106890)
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;381:1801–8. (PMID: 31633894874703210.1056/NEJMoa1908483)
Orhant E, Carling C, Chapellier J-F, Marchand J-L, Pradat P-F, Elbaz A, et al. A retrospective analysis of all-cause and cause-specific mortality rates in French male professional footballers. Scand J Med Sci Sports. 2022;32:1389–99. (PMID: 3561161310.1111/sms.14195)
Ueda P, Pasternak B, Lim C-E, Neovius M, Kader M, Forssblad M, et al. Neurodegenerative disease among male elite football (soccer) players in Sweden: a cohort study. Lancet Public Health. 2023;8: e256–65. (PMID: 10.1016/S2468-2667(23)00027-0)
Lehman EJ, Hein MJ, Baron SL, Gersic CM. Neurodegenerative causes of death among retired National Football League players. Neurology. 2012;79:1970–4. (PMID: 22955124409884110.1212/WNL.0b013e31826daf50)
McKee AC, Stein TD, Nowinski CJ, Stern RA, Daneshvar DH, Alvarez VE, et al. The spectrum of disease in chronic traumatic encephalopathy. Brain. 2013;136:43–64. (PMID: 2320830810.1093/brain/aws307)
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;138:389–99. (PMID: 31152201668929310.1007/s00401-019-02030-y)
Smith DH, Johnson VE, Stewart W. Chronic neuropathologies of single and repetitive TBI: substrates of dementia? Nat Rev Neurol. 2013;9:211–21. (PMID: 23458973451365510.1038/nrneurol.2013.29)
Chen GX, Douwes J, van den Berg L, Pearce N, Kromhout H, Glass B, et al. Occupational exposures to pesticides and other chemicals: a New Zealand motor neuron disease case–control study. Occup Environ Med. 2022;79:412–20. (PMID: 3531827510.1136/oemed-2021-108056)
Castanedo-Vazquez D, Bosque-Varela P, Sainz-Pelayo A, Riancho J. Infectious agents and amyotrophic lateral sclerosis: another piece of the puzzle of motor neuron degeneration. J Neurol. 2019;266:27–36. (PMID: 2984537710.1007/s00415-018-8919-3)
Asken BM, Sullan MJ, Snyder AR, Houck ZM, Bryant VE, Hizel LP, et al. Factors influencing clinical correlates of chronic traumatic encephalopathy (CTE): a review. Neuropsychol Rev. 2016;26:340–63. (PMID: 27561662550755410.1007/s11065-016-9327-z)
Cairns DM, Smiley BM, Smiley JA, Khorsandian Y, Kelly M, Itzhaki RF, et al. Repetitive injury induces phenotypes associated with Alzheimer’s disease by reactivating HSV-1 in a human brain tissue model. Sci Signal. 2025;18: eado6430. (PMID: 3977253010.1126/scisignal.ado6430)
Livingston G, Huntley J, Liu KY, Costafreda SG, Selbæk G, Alladi S, et al. Dementia prevention, intervention, and care: 2024 report of the Lancet standing Commission. Lancet. 2024;404:572–628. (PMID: 3909692610.1016/S0140-6736(24)01296-0)
Williams S, Robertson C, Starling L, McKay C, West S, Brown J, et al. Injuries in elite men’s rugby union: an updated (2012–2020) meta-analysis of 11,620 match and training injuries. Sports Med. 2022;52:1127–40. (PMID: 3485405910.1007/s40279-021-01603-w)
Van Pelt KL, Puetz T, Swallow J, Lapointe AP, Broglio SP. Data-driven risk classification of concussion rates: a systematic review and meta-analysis. Sports Med. 2021;51:1227–44. (PMID: 3372128410.1007/s40279-021-01428-7)
Warburton DER, Bredin SSD. Health benefits of physical activity: a systematic review of current systematic reviews. Curr Opin Cardiol. 2017;32:541–56. (PMID: 2870863010.1097/HCO.0000000000000437)
Rebar AL, Stanton R, Geard D, Short C, Duncan MJ, Vandelanotte C. A meta-meta-analysis of the effect of physical activity on depression and anxiety in non-clinical adult populations. Health Psychol Rev. 2015;9:366–78. (PMID: 2573989310.1080/17437199.2015.1022901)
McMillan TM, McSkimming P, Wainman-Lefley J, Maclean LM, Hay J, McConnachie A, et al. Long-term health outcomes after exposure to repeated concussion in elite level: rugby union players. J Neurol Neurosurg Psychiatry. 2017;88:505–11. (PMID: 2795152610.1136/jnnp-2016-314279)
Hume PA, Theadom A, Lewis GN, Quarrie KL, Brown SR, Hill R, et al. A comparison of cognitive function in former rugby union players compared with former non-contact-sport players and the impact of concussion history. Sports Med. 2017;47:1209–20. (PMID: 2755814110.1007/s40279-016-0608-8)
Hume PA, Quarrie KL, Lewis GN, Theadom A. Nz-rugbyhealth study: self-reported injury experience and current health of former rugby union and non-contact sport players. Sports Med. 2022;52:1701–13. (PMID: 35088235921339010.1007/s40279-021-01630-7)
Hind K, Konerth N, Entwistle I, Theadom A, Lewis G, King D, et al. Cumulative sport-related injuries and longer term impact in retired male elite- and amateur-level rugby code athletes and non-contact athletes: a retrospective study. Sports Med. 2020;50:2051–61. (PMID: 32671695757547410.1007/s40279-020-01310-y)
Davies MAM, Judge DA, Delmestri A, Kemp PTS, Stokes KA, Arden NK, et al. Health amongst former rugby union players: a cross-sectional study of morbidity and health-related quality of life. Sci Rep. 2017;7:11786. (PMID: 28959048562007710.1038/s41598-017-12130-y)
Decq P, Gault N, Blandeau M, Kerdraon T, Berkal M, ElHelou A, et al. Long-term consequences of recurrent sports concussion. Acta Neurochir. 2016;158:289–300. (PMID: 2671128610.1007/s00701-015-2681-4)
Cunningham J, Broglio S, Wilson F. Influence of playing rugby on long-term brain health following retirement: a systematic review and narrative synthesis. BMJ Open Sport Exerc Med. 2018;4: e000356. (PMID: 29719729592665110.1136/bmjsem-2018-000356)
Zimmerman KA, Laverse E, Samra R, Yanez Lopez M, Jolly AE, Bourke NJ, et al. White matter abnormalities in active elite adult rugby players. Brain Commun [Internet]. 2021. https://doi.org/10.1093/braincomms/fcab133 . (PMID: 10.1093/braincomms/fcab133348702028637800)
Guell X, Arnold Anteraper S, Gardner AJ, Whitfield-Gabrieli S, Kay-Lambkin F, Iverson GL, et al. Functional connectivity changes in retired Rugby League players: a data-driven functional magnetic resonance imaging study. J Neurotrauma. 2020;37:1788–96. (PMID: 3218358310.1089/neu.2019.6782)
Sharma A, Hind K, Hume P, Singh J, Neary JP. Neurovascular coupling by functional near infra-red spectroscopy and sport-related concussion in retired rugby players: the UK Rugby Health Project. Front Hum Neurosci [Internet]. 2020. https://doi.org/10.3389/fnhum.2020.00042 . (PMID: 10.3389/fnhum.2020.00042334245667785722)
Russell ER, Mackay DF, Lyall D, Stewart K, MacLean JA, Robson J, et al. Neurodegenerative disease risk among former international rugby union players. J Neurol Neurosurg Psychiatry. 2022;93:1262–8. (PMID: 36195436966924710.1136/jnnp-2022-329675)
Quarrie KL, Hopkins WG, Anthony MJ, Gill ND. Positional demands of international rugby union: evaluation of player actions and movements. J Sci Med Sport. 2013;16:353–9. (PMID: 2297523310.1016/j.jsams.2012.08.005)
Tooby J, Woodward J, Tucker R, Jones B, Falvey É, Salmon D, et al. Instrumented mouthguards in elite-level men’s and women’s rugby union: the incidence and propensity of head acceleration events in matches. Sports Med. 2023. https://doi.org/10.1007/s40279-023-01953-7 . (PMID: 10.1007/s40279-023-01953-73790642511127838)
Tucker R, Raftery M, Fuller GW, Hester B, Kemp S, Cross MJ. A video analysis of head injuries satisfying the criteria for a head injury assessment in professional Rugby Union: a prospective cohort study. Br J Sports Med. 2017;51:1147–51. (PMID: 2866321710.1136/bjsports-2017-097883)
Quarrie KL, Hopkins WG. Tackle injuries in professional rugby union. Am J Sports Med. 2008;36:1705–16. (PMID: 1849596710.1177/0363546508316768)
Bussey MD, Salmon D, Romanchuk J, Nanai B, Davidson P, Tucker R, et al. Head acceleration events in male community rugby players: an observational cohort study across four playing grades, from under-13 to senior men. Sports Med. 2024;54:517–30. (PMID: 3767662110.1007/s40279-023-01923-z)
Russell ER, Mackay DF, Stewart K, MacLean JA, Pell JP, Stewart W. Association of field position and career length with risk of neurodegenerative disease in male former professional soccer players. JAMA Neurol. 2021;78:1057–63. (PMID: 34338724832979310.1001/jamaneurol.2021.2403)
Patricios JS, Schneider KJ, Dvorak J, Ahmed OH, Blauwet C, Cantu RC, et al. Consensus statement on concussion in sport: the 6th international conference on concussion in Sport-Amsterdam, October 2022. Br J Sports Med. 2023;57(11):695–711. (PMID: 3731621010.1136/bjsports-2023-106898)
Milne B, Atkinson J, Blakely T, Day H, Douwes J, Gibb S, et al. Data resource profile: the New Zealand integrated data infrastructure (IDI). Int J Epidemiol. 2019. https://doi.org/10.1093/ije/dyz014 . (PMID: 10.1093/ije/dyz014312434477614620)
D’Souza S, Milne BJ, Li C, Anns F, Gardner A, Lumley T, et al. Kumanu Tāngata: the aftermatch study—protocol to examine the health outcomes of high-level male rugby union players using linked administrative data. BMJ Open Sport Exerc Med. 2024;10: e001795. (PMID: 383625641086817410.1136/bmjsem-2023-001795)
von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke JP. The strengthening the reporting of observational studies in epidemiology (STROBE) statement: guidelines for reporting observational studies. Lancet. 2007;370:1453–7. (PMID: 10.1016/S0140-6736(07)61602-X)
Akers C. New Zealand Rugby Register 1870–2015: the players, referees and administrators in First-Class Rugby. Palmerston North: New Zealand Rugby Museum; 2016.
New Zealand Rugby Union. Competitions Regulations Handbook [Internet]. New Zealand Rugby; 2021 [cited 2024 Nov 26]. https://www.nzrugby.co.nz/assets/2021-Competitions-Regulations-Handbook-June.pdf . Accessed 26 Nov 2024.
Quarrie K, Gianotti S, Murphy I. Injury risk in New Zealand Rugby Union: a nationwide study of injury insurance claims from 2005 to 2017. Sports Med. 2020;50:415–28. (PMID: 31506903698504410.1007/s40279-019-01176-9)
Walesby KE, Exeter DJ, Gibb S, Wood PC, Starr JM, Russ TC. Prevalence and geographical variation of dementia in New Zealand from 2012 to 2015: brief report utilising routinely collected data within the Integrated Data Infrastructure. Australas J Ageing. 2020;39:297–304. (PMID: 3239452710.1111/ajag.12790)
Haneuse S. Time-to-event analysis. Modern epidemiology. 4th ed. Philadelphia: Wolters Kluwer; 2021. p. 531–62.
Te Whatu Ora. interRAI New Zealand. Annual report 2023/24 [Internet]. Wellington, New Zealand: Te Whatu Ora; 2024 p. 12. https://www.interrai.co.nz/assets/Annual-Reports/interRAI-Annual-Report-2023-24.pdf . Accessed 27 June 2025.
Daneshvar DH, Mez J, Alosco ML, Baucom ZH, Mahar I, Baugh CM, et al. Incidence of and mortality from amyotrophic lateral sclerosis in National Football League athletes. JAMA Netw Open. 2021;4: e2138801. (PMID: 34910152867474610.1001/jamanetworkopen.2021.38801)
Chen GX, Douwes J, van den Berg LH, Glass B, McLean D, ’t Mannetje AM. Sports and trauma as risk factors for motor neurone disease: New Zealand case–control study. Acta Neurol Scand. 2022;145:770–85. (PMID: 35355246932157810.1111/ane.13615)
LoBue C, Wadsworth H, Wilmoth K, Clem M, Hart J, Womack KB, et al. Traumatic brain injury history is associated with earlier age of onset of Alzheimer disease. Clin Neuropsychol. 2017;31:85–98. (PMID: 2785554710.1080/13854046.2016.1257069)
Schaffert J, LoBue C, White CL, Chiang H-S, Didehbani N, Lacritz L, et al. Traumatic brain injury history is associated with an earlier age of dementia onset in autopsy-confirmed Alzheimer’s disease. Neuropsychology. 2018;32:410–6. (PMID: 29389151597509210.1037/neu0000423)
Gaetz M. The multi-factorial origins of Chronic Traumatic Encephalopathy (CTE) symptomology in post-career athletes: the athlete post-career adjustment (AP-CA) model. Med Hypotheses. 2017;102:130–43. (PMID: 2847881810.1016/j.mehy.2017.03.023)
European Parliament. Directorate General for Parliamentary Research Services. The precautionary principle: definitions, applications and governance: in depth analysis. [Internet]. LU: Publications Office; 2016 [cited 2023 Jul 26]. https://doi.org/10.2861/821468 .
Quarrie KL, Hopkins WG. Changes in player characteristics and match activities in Bledisloe Cup rugby union from 1972 to 2004. J Sports Sci. 2007;25:895–903. (PMID: 1747404310.1080/02640410600944659)
Romero JP, Benito-León J, Louis ED, Bermejo-Pareja F. Under reporting of dementia deaths on death certificates: a systematic review of population-based cohort studies. JAD. 2014;41:213–21. (PMID: 2458340310.3233/JAD-132765)
*Further Information*
*Background: Growing concern surrounds the risk of neurodegenerative diseases in high-level collision sports, but research on Rugby Union's connection to these diseases is limited.
Objective: This study sought to examine the long-term neurodegenerative disease risk associated with participation in high-level Rugby Union ('rugby'), utilising whole-population administrative records.
Methods: This retrospective cohort study in New Zealand compared males born between 1920 and 1984 who were active in high-level (provincial or higher) rugby between 1950 and 2000 (n = 12,861) with males from the general population (n = 2,394,300), matched by age, ethnicity, and birthplace. We used Cox proportional hazards models to assess risks of Alzheimer's disease, Parkinson's disease, motor neuron disease, and other dementias, ascertained using mortality and hospitalisation records from January 1988 to June 2023.
Results: A higher percentage of rugby players (6.5%) than males in the general population (5.2%) developed neurodegenerative diseases, with hazard ratios indicating players showed increased risks for any neurodegenerative disease (1.22; 95% confidence interval [CI] 1.14-1.30), Alzheimer's disease (1.61; 95% CI 1.42-1.83), and other dementias (1.23; 95% CI 1.14-1.33). Significant differences were not observed for Parkinson's disease (1.05; 95% CI 0.89-1.22) and motor neuron disease (1.16; 95% CI 0.83-1.63). In general, this increased risk among players compared to the general population began around the ages of 70-79 years. Compared to the general population, small to moderate increased risks of any neurodegenerative disease were observed for a backline playing position, provincial and/or amateur players, international and/or professional players, participation in ≥ 2 years of play, and participation in five or more matches.
Conclusions: High-level rugby participation amongst males in New Zealand is associated with a small to moderate increase in neurodegenerative disease rates compared to the general population.
(© 2025. The Author(s).)*
*Declarations. Funding: This work was supported by World Rugby Limited and the New Zealand Rugby Foundation (Grant number G-2004-00963). The study funders had no role in study conception or design, data collection, data analysis, data interpretation, or writing of the manuscript. World Rugby obtained an independent, external review of the project plan prior to funding. Conflict of interest: Financial interests: SD, BM, CL, SM, and TL’s research time was funded through their employment contracts with the University of Auckland, supported in part by the grant from World Rugby Limited. SD’s research time was also funded by the New Zealand Rugby Foundation. KQ has been employed by New Zealand Rugby since 2000 and currently occupies the role of Chief Scientist, New Zealand Rugby. He has received funding for travel and accommodation to attend World Rugby’s medical meetings. AJG is a contracted concussion consultant to Rugby Australia. He is the global clinical lead for the Word Rugby Brain Health Service. He has received travel funding or been reimbursed by professional sporting bodies and commercial organisations for discussing or presenting sport-related concussion research at meetings, scientific conferences, workshops, and symposiums. He has a clinical practice in neuropsychology involving individuals who have sustained sport-related concussion (including current and former athletes). He is supported by a National Health and Medical Research Council (NHMRC) Investigator Grant. He acknowledges unrestricted philanthropic support from the National Rugby League for research in former elite-level rugby league players. IM was employed by New Zealand Rugby from 2012 to 2019 as the Chief Medical Officer. Non-financial interests: KQ was a member of World Rugby’s Scientific Committee from 2014 to 2024, and has contributed to various World Rugby working groups focussed on player welfare issues from 2011 to the time of publication. His input into the project was conducted in collaboration with his co-authors, who are independent of New Zealand Rugby, and he declares that at no time did New Zealand Rugby, nor the funding agencies World Rugby and the New Zealand Rugby Foundation, provide advice or input into the data analysis, interpretation of the findings, or the manuscript preparation. A copy of the submitted draft of the project was provided to the funding bodies and New Zealand Rugby at the time of submission. AJG is a member of the World Rugby Concussion Working Group and the Australian Football League Concussion Scientific Advisory Committee. IM has held various committee appointments with World Rugby focused on player welfare matters. All other authors declare no relevant financial or non-financial interests. Availability of data and material: The data analysed in this study were housed in the New Zealand IDI, which is administered by Statistics New Zealand. Anonymised individual-level data in the IDI can only be accessed via secure data laboratories, and only export of approved aggregated results, as presented herein, is permitted under New Zealand privacy regulations. Permission to access data is only granted upon application to Statistics New Zealand as part of bona fide research projects. For these reasons, data cannot be made generally available. Note, these results are not official statistics. They have been created for research purposes from the IDI, which is carefully managed by Statistics New Zealand. For more information about the IDI, please visit https://www.stats.govt.nz/integrated-data/ . Access to the data was approved under project MAA2016-21. Ethics approval: Ethics approval was granted by the Auckland Health Research Ethics Committee (ref. AH23203). Code availability: Statistical code for analyses can be made available from the corresponding author upon request. Author contributions: CW and KQ conceived the project and digitised the data from the New Zealand Rugby Register so that it could be loaded into the New Zealand IDI. KQ, BM, SD, SM, CW, AG, IM, EV, and TL contributed to overall project planning and development of the funding application. Analyses were planned by SD, BM, KQ, FA, CL, TL, and SM. Analyses were conducted by FA, CL, SD, and BM. FA, KQ, SD, and BM drafted the report. All authors contributed to final drafting and editing and accept responsibility for the decision to submit the report for publication. Access to data for analyses in the IDI environment was restricted to CW, BM, FA, SD, and CL.*