Breakthrough study reveals repetitive head impacts are a definitive cause of CTE

Sports organizations must acknowledge that head impacts cause CTE to protect children

(Boston) – A new analysis by leading international experts on chronic traumatic encephalopathy (CTE) found conclusive evidence that repetitive head impacts (RHI) cause the degenerative brain disease CTE.

The researchers from Harvard University, Boston University, University of Sydney (Australia), University of Auckland (New Zealand), University of Michigan, University of California-San Francisco, University of Sao Paulo (Brazil), University of Melbourne (Australia), Oxford Brookes University (UK) and the Concussion Legacy Foundation are issuing a global call to action to sports organizations, government officials, and parents to immediately implement CTE prevention and mitigation efforts, especially for children.

The researchers analyzed the data through the “Bradford Hill criteria”, a trusted set of nine benchmarks developed by one of the pioneers of smoking and lung cancer research to gauge the confidence science can place in a causal relationship between an environmental exposure and an adverse health outcome.

Among the revelations in the analysis, the authors discovered that the brain banks of the US Department of Defense, Boston University-US Department of Veterans Affairs, and Mayo Clinic have all published independent studies on distinct populations showing contact sport athletes were at least 68 times more likely to develop CTE than those who did not play contact sports. This incredible strength of association, combined with robust evidence in all nine benchmarks, is conclusive evidence of causation.

“This innovative analysis gives us the highest scientific confidence that repeated head impacts cause CTE,” said study lead author Dr. Chris Nowinski, Concussion Legacy Foundation CEO. “Sport governing bodies should acknowledge that head impacts cause CTE and they should not mislead the public on CTE causation while athletes die, and families are destroyed, by this terrible disease.”

The most studied causes of CTE are contact and collision sports, which include soccer, rugby, boxing, American football, Canadian football, and Australian rules football. The study authors are concerned parents and coaches, who have the most control over whether children are exposed to repetitive head impacts, are not getting the facts from global sports organizations, and are exposing their children to preventable cases of CTE.

While both the United States Centers for Disease Control and Prevention (CDC) and the National Football League (NFL) acknowledge a causal relationship between repetitive head impacts and CTE, global sporting organizations including Fédération Internationale de Football Association (FIFA), World Rugby, International Olympic Committee (IOC), National Hockey League (NHL), Canadian Football League (CFL), National Collegiate Athletic Association (NCAA), Australian Football League (AFL), National Rugby League (NRL) and New Zealand Rugby thus far have refused to publicly acknowledge a causal relationship.

Researchers say it is the duty of these organizations to inform athletes and their families and take appropriate steps toward CTE prevention and mitigation. Many of the organizations, including the NFL, spend millions of dollars a year recruiting athletes, including children, without disclosing the risk of CTE.

“This analysis shows it is time to include repetitive head impacts and CTE among child protection efforts like exposure to lead, mercury, smoking, and sunburns,” said Dr. Adam Finkel, Clinical Professor of Environmental Health Sciences at the University of Michigan School of Public Health and a former Director of Health Standards, US Occupational Safety and Health Administration (OSHA). “Repetitive head impacts and CTE deserve recognition in the global public health discussion of preventable disorders caused by childhood exposures.”

CTE can only be definitively diagnosed through a post-mortem examination of the brain. Scientists don’t yet know how many athletes, military Veterans, and others exposed to head impacts have CTE, but knowing the prevalence of a disease is not required to enact disease prevention efforts, especially as the global scientific community closes in on 1,000 CTE cases diagnosed worldwide in the last decade.

“Even we were surprised by how strong the causal relationship between repetitive head impacts and CTE becomes when the data are analyzed within the appropriate framework and in an unbiased manner,” said study co-senior author Dr. Robert Cantu Concussion Legacy Foundation medical director. “Scientists and policymakers must retire the word association and begin using causation in all forums in an urgent effort to educate the public.”

The authors urge governments to support CTE research and prevention efforts since CTE is associated with developing dementia, which comes with extraordinary healthcare costs.

The research paper, Applying the Bradford Hill Criteria for Causation to Repetitive Head Impacts and Chronic Traumatic Encephalopathy, is published in Frontiers in Neurology, and can be viewed online.

Dr. Nowinski and Dr. Finkel answered some of the most frequently asked questions about CTE causation, read their blog here.