Three in four, once you count the brains nobody donated

Chronic traumatic encephalopathy, CTE, can only be diagnosed after death, and only in brains that families choose to donate¹. That has always been the problem with the numbers. Donors are not a random sample: families of players who had symptoms are more likely to give¹. A study published this week in JAMA Network Open tries to correct for exactly that bias¹.

Researchers at Boston University, Mass General Brigham and the Concussion & CTE Foundation studied 387 deceased former NFL players whose brains were donated; 362 of them, 94%, had some degree of CTE pathology¹. They then went to the dull records: National Death Index death certificates for all 2,362 NFL players who died between 2008 and 2023, including how many died of neurodegenerative disease or had dementia¹. Players with cognitive symptoms turned out to be about five times more likely to be donated¹. Adjusting for that, the estimate for all deceased players is 74.5%¹. An August study by the same group could only say somewhere between 25% and 98%¹.

For comparison, CTE has been seen in under 1% of thousands of donors to community brain banks in the United States, Australia, Austria and Brazil¹. The authors add a fair caution: the estimate covers players who have died, and does not predict how many living former players or active players are affected¹. Not everyone with CTE pathology develops symptoms, particularly in early-stage disease¹.

This is occupational health in its plainest form: a job, a repeated exposure, and a measured outcome. Earlier work found NFL players develop dementia at four times the rate of the general population¹. Matt Hasselbeck, an 18-year NFL veteran who supports the research, said he was looking at the findings “like getting a scouting report”¹.

The researchers’ advice to former players worried about their brain health is concrete: see a clinician who specialises in neurodegenerative conditions, and work on the risk factors that can be changed¹. It is sound advice for anyone whose job or sport meant years of hits to the head, and it starts with a phone call, not a scan.