To Whom it May Concern:

As scientists, physicians, researchers, and public health experts, we believe the relationship between repetitive head impacts (RHI) and chronic traumatic encephalopathy (CTE) should no longer be referred to as an ‘association’. Rather, we believe that the available evidence demands the relationship between RHI and CTE should only be described as causal.

We respectfully request your organization update all position papers and public-facing statements to reflect the current scientific understanding in an urgent effort to educate the public.

As you consider this request, we ask that you review a recently published analysis of the evidence for RHI causality in CTE using the Bradford Hill criteria. The Hill criteria were created specifically to provide a methodology for reviewing epidemiologic research to determine when it is appropriate to move from labeling an observed relationship as an association to causation.

The review, entitled Applying the Bradford Hill Criteria for Causation to Repetitive Head Impacts and CTE, was published Frontiers in Neurology on July 22. The evidence for causation has strengthened considerably in the last few years, specifically in strength of association, biological gradient, consistency, plausibility, and coherence.

The authors conclude that the evidence in favor of RHI as a causal pathway leading to CTE is compelling enough to move from “association” to “causation.” We agree with this conclusion, and we support creating policies to prevent CTE in the next generation of contact sport athletes and others exposed to repetitive head impacts.

We recognize that RHI may someday be found to not be the only risk factor or precipitant to CTE, as many diseases have multiple causes. However, it is time to publicly acknowledge that RHI is a causative factor which can lead to CTE.

In August, we petitioned the National Institute of Neurological Disorders and Stroke (NINDS) to review this evidence and update their statement on causation. On October 5, 2022, NINDS updated their official statement on CTE to “CTE is a delayed neurodegenerative disorder that was initially identified in postmortem brains and, research-to-date suggests, is caused in part by repeated traumatic brain injuries.”

To many, this is not new information. The idea that boxing causes progressive neurodegeneration has been widely accepted for nearly a century. In 2019, the U.S. Centers for Disease Control and Prevention (CDC) issued a fact sheet, stating, “The research to-date suggests that CTE is caused in part by repeated traumatic brain injuries, including concussions, and repeated hits to the head, called subconcussive head impacts.”

Besides NINDS and CDC, organizations that now utilize or publicly support causation language include the NFL in the United States, the National Health Service, Football Association, and Professional Footballer’s Association in the United Kingdom, and the Australian Football League.

We have created an online dashboard listing organizations that recognize the role of RHI and rTBI in CTE causation, and we also list organizations that explicitly do not or have not made public statements. Please let us know if we do not have your organization listed appropriately.

We look forward to your response and are available individually or as a group to respond to any questions you may have.


Mike Alosco, PhD
Associate Professor of Neurology
Co-director, Alzheimer’s Disease Center Clinical Research Core
Principal Investigator, CTE Center
Boston University School of Medicine

Breton Asken, PhD, ATC
Assistant Professor
Department of Clinical and Health Technology
University of Florida
Fixel Institute for Neurological Diseases

Rhoda Au, PhD
Professor of Anatomy & Neurobiology, Neurology and Epidemiology
Boston University Schools of Medicine and Public Health

Kathleen Bachynski, PhD, MPH
Assistant Professor of Public Health
Muhlenberg College

Kevin Bieniek, PhD
Director, Glenn Biggs Institute for Alzheimer’s & Neurodegenerative Diseases Brain Bank
Neuropathology Core Leader, South Texas Alzheimer’s Disease Research Center
Assistant Professor, Department of Pathology & Laboratory Medicine
University of Texas Health Science Center at San Antonio

Charles Bernick, MD, MPH
Clinical Professor of Neurology
University of Washington

Yelena Bogdanova, PhD, PhD
Assistant Professor of Psychiatry 
Boston University School of Medicine

Michael Buckland, MBBS, PhD, FRCPA, FFSc (RCPA)
Clinical Associate Professor of Pathology, School of Medical Sciences, University of Sydney
Head of the Department of Neuropathology at Royal Prince Alfred Hospital
Founding & Executive Director, Australian Sports Brain Bank

Samantha Bureau, PhD
Director of Programs
Concussion Legacy Foundation

Clinical Professor of Neurology
Boston University School of Medicine

Stephen T. Casper, PhD
Professor, Humanities and Social Sciences
Clarkson University

David X. Cifu, MD
Associate Dean of Innovation and System Integration and Eminent Scholar
Herman J. Flax, MD Professor and Chair, Department of Physical Medicine and Rehabilitation
Senior Consultant, Sheltering Arms Institute
Virginia Commonwealth University School of Medicine
Senior TBI Specialist, U.S. Department of Veterans Affairs
Principal Investigator, Long-term Impact of Military-relevant Brain Injury Consortium Chronic Effects of Neurotrauma Consortium (LIMBIC-CENC)

John F. Crary, MD, PhD
Director, Neuropathology Brain Bank & Research Core
Director, Physician Scientist Track in Experimental Pathology
Department of Pathology
Nash Family Department of Neuroscience
Department of Artificial Intelligence & Human Health
Friedman Brain Institute
Ronald M. Loeb Center for Alzheimer’s Disease
Icahn School of Medicine at Mount Sinai

Jeffrey L. Cummings, MD, ScD
Joy Chambers-Grundy Professor of Brain Science
Director, Chambers-Grundy Center for Transformative Neuroscience
Department of Brain Health, School of Integrated Health Sciences
University of Nevada Las Vegas (UNLV)

Maurice Curtis, PhD
Professor of Neuroscience
Head of Department, Anatomy and Medical Imaging
Co-Director of the Neurological Foundation Human Brain Bank
The University of Auckland

Daniel Daneshvar, MD, PhD
Assistant Professor
Assistant Chair for Research, Department of PM&R
Harvard Medical School

Steven T. DeKosky, MD, FACP, FANA, FAAN
Deputy Director, McKnight Brain Institute
Aerts-Cosper Professor of Alzheimer’s Research
Professor of Neurology and Neuroscience
Associate Director, 1Florida ADRC
University of Florida

Marc Diamond, MD
Director, Center for Alzheimer's and Neurodegenerative Diseases
Professor of Neurology and Neuroscience
Peter O’Donnell Jr. Brain Institute
University of Texas, Southwestern Medical Center

Ramon R. Diaz-Arrastia, MD, PhD
Director of Traumatic Brain Injury Clinical Research Center
Associate Director for Clinical Research, Center for Neurodegeneration and Repair
John McCrea Dickson M.D. Presidential Professor
University of Pennsylvania Perelman School of Medicine

Dennis W. Dickson, MD
Robert E. Jacoby Professor of Alzheimer's Research
Neuropathology and Microscopy Laboratory
Mayo Clinic

David W. Dodick, MD
Professor Emeritus/Founder/Director of Sport Neurology & Concussion Program, Mayo Clinic Arizona
Chair, International Concussion Society
Chair, American Brain Foundation
Chief Science Officer, Atria Institute
Chair, Atria Academy of Science and Medicine
Affiliate Professor, University of Copenhagen
Adjunct Professor, Norwegian University of Science and Technology

Margaret Esiri, DM, FRCPath
Emeritus Professor of Neuropathology, Oxford University

Sir Richard Faull, MBCHB, DSc, KNZM, FRSNZ
University Distinguished Professor
Director, Centre for Brain Research
Founder and Director, Neurological Foundation Human Brain Bank
The University of Auckland

Adam M. Finkel, ScD, CIH
Clinical Professor of Environmental Health Sciences
University of Michigan School of Public Health
Director of Health Standards, US Occupational Safety and Health Administration, 1995-2000

Sam Gandy, MD, PhD
Mount Sinai Endowed Chair in Alzheimer’s Disease Research
Professor of Neurology and of Psychiatry
Director, Mount Sinai Center for Wellness and Cognitive Health
Icahn School of Medicine at Mount Sinai

Lee E. Goldstein, M.D., Ph.D.
Associate Professor of Psychiatry Radiology, Neurology, Pathology & Laboratory Medicine, Biomedical Engineering, Boston University School of Medicine & College of Engineering
Co-Leader, Biomarker Core, Boston University Alzheimer Disease and CTE Center

Michael J. Grey, PhD
Reader in Rehabilitation Neuroscience, University of East Anglia

Lea T. Grinberg, MD, PhD
John Douglas French Alzheimer’s Foundation Endowed Professor
Professor in Residence - Departments of Neurology and Pathology
Co-leader, Memory and Aging Center, Neurodegenerative Disease Brain Bank
Global Brain Health Institute, Faculty and Member of the Executive Committee
Institute of Computational Health Sciences, Faculty, UCSF

Elisa Hill-Yardin, PhD
Associate Professor
School of Health and Biomedical Sciences
Royal Melbourne Institute of Technology

Sidney R. Hinds II, MD, FAAN
COL (retired), United States Army
Assistant Professor, Neurology/Radiology
Uniformed Services University
Co-PI & Lead, External Collaborations,
Long-term Impact of Military-relevant Brain Injury Consortium-Chronic Effects of Neurotrauma Consortium (LIMBIC-CENC)

Kenneth S. Kosik, MD
Hariman Distinguished Professor of Neuroscience
Co-Director, Neuroscience Research Institute
Santa Barbara, CA

Chester Mathis, PhD
Distinguished Professor of Radiology
University of Pittsburgh
UPMC Endowed Chair of PET Research

Ann McKee, MD
William Fairfield Warren Distinguished Professor of Neurology and Pathology
Boston University School Medicine
Director, BU CTE Center
Chief, Neuropathology VA Boston

Jesse Mez, MD
Associate Professor of Neurology
Co-director, Alzheimer’s Disease Center Clinical Research Core
Boston University School of Medicine

Michael D. McClean, ScD
Associate Dean for Research and Faculty Advancement
Professor of Environmental Health
Boston University School of Public Health

Bruce Miller, MD
A.W. and Mary Margaret Clausen Distinguished Professor in Neurology
Director, Memory and Aging Center
Co-Director, Global Brain Health Institute
University of California, San Francisco (UCSF)

Helen Murray, PhD
Research Fellow, Centre for Brain Research
Department of Anatomy and Medical Imaging
The University of Auckland

Christopher Nowinski, PhD
CEO, Concussion Legacy Foundation
Executive Committee, Boston University Alzheimer’s Disease Research Center

Alan Pearce, PhD
Research Manager, Australian Sports Brain Bank (Victoria)
Adjunct Associate Professor
School of Allied Heath, Human Services & Sport
La Trobe University

Gil Rabinovici, MD
Edward Fein & Pearl Landrith Distinguished Professor
Director, UCSF Alzheimer’s Disease Research Center
Departments of Neurology, Radiology and Biomedical Imaging
University of California, San Francisco (UCSF)

Philip Schatz, Ph.D.
Professor of Psychology
Saint Joseph's University

Julie Stamm, PhD, ATC
Clinical Assistant Professor
Department of Kinesiology, University of Wisconsin-Madison

Judith A. Steen, PhD
Director of the Neuroproteomics Laboratory | Associate Professor
Boston Children’s Hospital | Harvard Medical School

Thor D. Stein, MD, PhD
Associate Professor of Pathology & Laboratory Medicine
Co-Leader of the Neuropathology Core
Boston University Alzheimer Disease and CTE Center
Boston University School of Medicine

Robert Stern, PhD
Professor of Neurology, Neurosurgery, and Anatomy & Neurobiology
Director of Clinical Research, BU CTE Center
Senior Investigator, BU Alzheimer’s Disease Research Center
Boston University School of Medicine

Michael J. Stuart, MD
Professor, Department of Orthopedics and Sports Medicine
Mayo Clinic

Catherine Suter, PhD
Chief Scientist, Australia Sports Brain Bank
Department of Neuropathology at Royal Prince Alfred Hospital
School of Medical Sciences, University of Sydney

Carmela Tartaglia, MD, FRCPC
Marion and Gerald Soloway Chair in Brain Injury and Concussion Research
Associate Professor, Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto
Co-director Memory Clinic - Toronto Western Hospital
Director Memory Clinical Trials Unit

Charles H. Tator, OC, MD, PhD, FRCSC, FACS
Professor of Neurosurgery, University of Toronto
Founder, ThinkFirst Canada and Parachute Canada
Director, Canadian Concussion Centre

Neil Vasdev, PhD ACSF, FRSC (UK), FSNMMI
Canada Research Chair in Radiochemistry and Nuclear Medicine
Azrieli Endowed Chair in Brain and Behaviour
Professor, Department of Psychiatry, University of Toronto
Associate Professor of Radiology, Harvard Medical School
Director, Azrieli Centre for Neuro-Radiochemistry, Centre for Addiction & Mental Health (CAMH)
Director & Chief Radiochemist, CAMH Brain Health Imaging Centre

Jennifer Weuve, MPH, ScD
Associate Professor, Department of Epidemiology
Boston University School of Public Health

Adam White, PhD
Senior Lecturer in Sport & Coaching Sciences
Department of Sport, Health Sciences and Social Work
Oxford Brookes University

Kristine Yaffe, MD
Professor of Psychiatry, Neurology and Epidemiology, Psychiatry
University of California San Francisco School of Medicine
Weill Institute for Neurosciences
Roy and Marie Scola Endowed Chair
Vice Chair of Research in Psychiatry

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