Estimated CTE Rate Among Deceased NFL Players Remains High After Donation Bias Adjustment

A new estimate suggests chronic traumatic encephalopathy (CTE) may have affected about three in four former NFL players who died between 2008 and 2023. The finding accounts for the fact that families of players with memory or thinking problems were more likely to donate their brains for research. It still points to a substantial burden, but it cannot tell us how common CTE is among all former players, including those who are alive.

Researchers began with more than 375 donated brains that had a clear result. Evidence of CTE appeared in 94 percent. That high proportion cannot be read as the rate among all former players: brain donation is more likely when families have seen symptoms that may be associated with the disease.

To estimate a broader rate, the researchers compared donation records with national death records for 2,362 former NFL players who died during the 16-year period. Players who had dementia or other problems with memory and thinking before death were about five times as likely to have their brains donated. After adjusting for that difference, the team estimated that 74.5 percent of the players who died had CTE. Under much stricter assumptions about who donated, the estimate remained above 60 percent.

What the estimate can—and can’t—show

The estimate is a statistical model for players whose brains were never examined. It isn’t a direct count of confirmed cases, and its accuracy depends on how well the researchers’ assumptions capture the factors that influence donation. The authors said their estimates held up across a range of assumptions, but other influences may be harder to measure.

For example, Rachel Grashow, PhD, a senior research scientist at the Harvard T.H. Chan School of Public Health who studies living former NFL players, noted that families may not have known about or recognized symptoms such as depression before a player’s death. The study also didn’t report other brain diseases found at autopsy that can contribute to dementia, including Alzheimer’s disease. James Kelly, MD, a neurologist who wasn’t involved in the research, described the result as an elaborate estimate and questioned how much it adds to what’s already known.

The researchers estimated that 27 percent of all the former players had dementia during their lives, though they said this figure is likely too low. An earlier study from the same group estimated a much wider possible range—25 to 98 percent—for former players who died between 2016 and 2021, because the team couldn’t determine how representative brain donors were. The newer analysis narrows that uncertainty, but it doesn’t remove it.

Nor can the results be applied directly to living former players. Grashow cautioned that players who died earlier may have been more likely to die from illnesses related to CTE, which may not reflect the health of people who are still living. CTE can be confirmed only by examining brain tissue after death, so symptoms in a living person can’t establish that diagnosis.

Why repeated impacts matter

CTE is a brain disease linked to repeated head impacts. It can worsen over time, though some people with the disease, especially at an early stage, may have no noticeable symptoms. When symptoms occur, they can include changes in memory and thinking, behavior changes, and dementia. The only established risk factor described by the study’s senior author, Yorghos Tripodis, PhD, is repetitive head impacts.

Many impacts don’t cause a diagnosed concussion or immediate symptoms. Tripodis said the accumulated number of hits over time may be more relevant to CTE than the number of concussions alone. In earlier research among brain donors, each additional year of football was associated with about 30 percent higher odds of CTE. That association comes from donated brains, however, and does not mean that every player will develop the disease or symptoms.

Football’s safety measures have changed over time. The NFL has introduced penalties for certain helmet-to-helmet contact, required padded Guardian Caps for some players during full-contact practices, changed its kickoff format in 2024, and increased the share of players using helmets that rank highest in the league’s lab testing. More than 98 percent of players were using those helmets by the time the source reported its figures, compared with about 70 percent before the 2025 season began. The league also reported that kickoff concussions remained below the rate under the previous format.

These changes may reduce the force or consequences of some impacts, but they don’t necessarily reduce the total number of hits. Kelly said the evidence on Guardian Caps is contested and that league data doesn’t show the caps alone explain a decline in concussions. A lower concussion rate therefore doesn’t establish that long-term CTE risk has fallen. About four in ten players in the study were at least 80 when they died, and many played before recent safety changes.

Practical context for players and families

Tripodis said delaying the start of tackle football can reduce the total number of impacts a child accumulates, potentially lowering later risk. The study did not test a specific starting age or quantify how much this change might affect an individual’s health. Its findings support attention to cumulative exposure while leaving important questions about prevention unanswered.

For former players with memory, mood, sleep, or other health concerns, CTE isn’t the only possible explanation. Grashow’s research involving about 5,000 living former NFL players has found links between head injuries and several treatable conditions, including sleep apnea, low testosterone, high blood pressure, depression, anxiety, and ringing in the ears. These conditions can affect thinking and memory, and some can harm brain and heart health when left untreated. A healthcare provider can help assess symptoms and consider treatable causes before anyone assumes CTE is responsible.

Grashow also warned that presenting brain disease as inevitable can worsen distress, particularly because former players may be vulnerable to depression and suicidal thoughts. The study offers a concerning estimate for players who have died, but it does not mean that every former player has CTE or will develop symptoms. For those seeking confidential support, the NFL Life Line is available around the clock at 800-506-0078. Research that follows living players and improves the ways CTE is identified will help clarify what these findings mean for people today.