CTE Found in at Least 1 in 4 Former NFL Players Who Died in 2016–2021

At least 24.5% of former NFL players who died between 2016 and 2021 had chronic traumatic encephalopathy, according to a study published August 25 in The BMJ. The finding concerns disease identified after death in a defined group of former players. It does not establish that one in four current players has CTE or will develop it. The BMJ study

Researchers led by Daniel Daneshvar included former players who debuted in the NFL after 1949 and played at least one NFL game. The full study covered 1,712 deaths from 2008 through 2021, including 338 brain donors. The widely reported one-in-four figure came from the later six years, when donation was more frequent. Study eligibility, Harvard Medical School’s account

How the researchers reached one in four

Of the 878 former players who died during 2016–21, 235 donated their brains for examination. Researchers found CTE in 215, leaving 20 examined brains without the disease and 643 players whose brains were not studied. The researchers’ foundation summary

The minimum comes from dividing the 215 confirmed cases by all 878 deaths. That produces 24.5%, even if every unexamined brain was free of CTE. Dividing only by the donated brains gives about 91%, which describes the examined group rather than all the deaths.

The opposite assumption, that all 643 unexamined brains had CTE, produces 858 cases among 878 deaths, or 97.7%. Those figures mark the possible range allowed by the missing examinations. They do not identify a precise rate within it. Mass General Brigham’s explanation

Why brain donation matters

Families concerned about a player’s cognitive or behavioral decline may be more likely to donate a brain. Donors also differed from non-donors in career length and football honors. Those differences complicate treating donors as representative of every former player. Counting confirmed cases against all deaths establishes a minimum without assuming that donors and non-donors had the same disease rate. Harvard Medical School

What CTE means

CTE is a brain disease associated with long-term exposure to repeated head impacts, including impacts without concussion symptoms. The CDC says a history of one or more concussions, or occasional head impacts, does not by itself establish that someone will develop CTE. Confirmation currently requires examination of brain tissue after death. CDC explanation

Traumatic encephalopathy syndrome, or TES, is a related research classification based on clinical features and exposure history. Meeting TES criteria is not the same as having CTE confirmed through a brain examination. The consensus criteria were developed to support research. NINDS consensus criteria, published in Neurology

What the study found about dementia

Across the full donor group, study clinicians identified dementia in 202 people. Advanced, stage IV CTE was associated with a higher risk of dementia after statistical adjustment. That association cannot establish that CTE alone caused each person’s dementia, particularly when other brain diseases were also present. The BMJ study

The debate over applying the findings

In correspondence published after the study, Marc Weisskopf and colleagues at Harvard’s Football Players Health Study agreed that the reported ranges were valid for the deaths analyzed. They challenged applying those ranges to all NFL players, because most eligible players were still living and those who died were not a random sample. This was methodological correspondence, rather than a new prevalence study. Original August 31 response

Symptoms still warrant medical assessment. Harvard researcher Rachel Grashow, who was not involved in the August study, noted that treatable conditions, including sleep apnea and high blood pressure, can cause symptoms people associate with CTE. Concern about the disease should not prevent evaluation for those conditions. Harvard Chan School