Researchers have diagnosed CTE in 345 of 376 of NFL players studied: What do the numbers tell us?

By Dr. Chris Nowinski, Concussion Legacy Foundation co-founder and CEO

Today the Boston University CTE Center released they have now diagnosed CTE in 345 of 376 (91.7%) NFL players studied at the UNITE Brain Bank since it was co-founded in 2008 by Boston University, the VA Boston Healthcare System, and the Concussion Legacy Foundation. These numbers are updated from the 2017 publication in the Journal of the American Medical Association that reported 110 of 111 NFL players (99%) had CTE.

A lot has happened since that 2017 study that helps us interpret what these new NFL numbers mean. Before we get to that, the goal of releasing the numbers is to drive those at risk for CTE to resources and research.

“While the most tragic outcomes in individuals with CTE grab headlines, we want to remind people at risk for CTE to know that those experiences are in the minority,” said Ann McKee, MD, director of the BU CTE Center and chief of neuropathology at VA Boston Healthcare System. “Your symptoms, whether or not they are related to CTE, likely can be treated, and you should seek medical care. Our clinical team has had success treating former football players with mid-life mental health and other symptoms.” Here are links to resources and research opportunities:

1. Symptoms that could be related to CTE or concussion can be effectively treated. Reach out to the CLF HelpLine for treatment recommendations and support.
2. CLF is collaborating with the BU CTE Center to learn how to prevent, diagnose and treat CTE and other symptoms related to head impacts, including Project S.A.V.E., which is recruiting men and women over the age of 50 who played contact sports. To learn about studies with active recruiting, click here.
3. To sign up for our research registry to be informed of future studies, click here.

It is difficult even for experts to interpret what 345 of 376 NFL players having CTE means. Here are some ways to understand the data:

1. The study does not necessarily mean that 92% of all current and former NFL players have CTE. Brain bank samples are subject to selection biases. The prevalence of CTE among NFL players is unknown since CTE can only be definitively diagnosed after death.

2. College, high school, and youth players face lesser odds of being diagnosed with CTE. A 2020 study from the UNITE Brain Bank found the odds of being diagnosed with CTE increase by 30% per year of football played.

3. The odds of an NFL player getting CTE appear extraordinarily higher than people who haven’t played contact sports. For comparison, a 2018 Boston University study of 164 brains of men and women donated to the Framingham Heart Study found that only 1 of 164 (0.6 percent) had CTE. The lone CTE case was a former college football player. The extremely low population rate of CTE is in line with similar studies from brain banks in Austria, Australia and Brazil.

4. The data provides more evidence that repeated traumatic brain injuries and repetitive head impacts cause CTE. In 2022 we published a review of the CTE literature and concluded the evidence is overwhelming that sports like football cause CTE. The National Institutes of Health agreed and three months later updated their definition of CTE.

5. As the study sample size grew, we expected the 99% odds from 2017 to decrease to something closer to the actual prevalence. The small drop in odds from 99% to 92% with a much larger sample is concerning. In 2017, CTE critics said we were getting “the worst of the worst” in those first eight years of the brain bank, so the 99% number was meaningless. In the intervening six years, we’ve more than tripled the sample size, and yet still more than 90% of players have CTE.

This leaves us with two important questions:

1. Does the high CTE odds suggest that if we were able to diagnose CTE in the living, we’d learn that a very high share of NFL players (>50%) have CTE?
2. Or, if we are still getting the worst of the worst, most symptomatic cases, does that mean that among NFL players, CTE can be easily diagnosed by families? If so, how can we turn that into a diagnostic protocol for doctors?

CLF is here for current and former NFL players and their families who may be worried about CTE. Submit a form to the CLF HelpLine and our staff will be in touch to provide personalized support and resources. We also offer Zoom support groups for suspected CTE patients and caregivers to discuss shared experiences. Learn more here, and know above all: you are not alone, and help is available.

We are very grateful to our Legacy Donors and their families for making this research possible, and the for the scientists for their commitment to understanding and treating CTE. Without their contributions, we wouldn’t know anything about CTE, or have any new data to release. Read their stories here.