A new report has added to the growing debate of the dangers of head injuries in professional sport with nearly a quarter of all former National Football League (NFL) players who died from 2016 to 2021 having confirmed chronic traumatic encephalopathy (CTE) – a neurodegenerative disease linked to repeated head impacts  – at death.

Players whose brains showed the most advanced CTE (stage IV) were also more likely to have symptoms typical of dementia before death, such as memory loss and impaired cognitive function, the study found.

Previous studies have shown that people who experience repetitive head impacts from contact sports, including NFL players, are more likely to develop and die from neurodegenerative disease such as CTE than the general population.

However, CTE can only be confirmed by post-mortem examination, so the extent of CTE among NFL players and its association with symptoms such as dementia has been unclear.

To address this, the researchers studied brain tissue donated to the UNITE brain banks at the Boston University CTE Centre (333 donors) and Mount Sinai (1 donor), and UCSF ADRC brain bank (4 donors) by American football players who died between 2008 and 2021 and had played at least one NFL game after 1949 (the first year plastic helmets were mandatory) to estimate rates of CTE among this group.

They also accessed players’ medical notes for symptoms typical of dementia during life and reviewed medical histories from clinical interviews with family members or other informants to examine the association between advanced stage CTE and dementia.

Study clinicians confirmed dementia cases and cause of death using all available information. Average age at death was 66.5 years.

It found among 1,712 NFL players who died from 2008 to 2021, 338 (19.7%) players’ brains were studied, 315 (93.2%) of whom had a diagnosis of CTE; thus, the possible CTE prevalence at death ranged between 18.5% and 98.7%.

Among those who died from 2016 to 2021, when brain donation was most frequent, the possible CTE prevalence at death ranged between 24.5% and 97.7%.

Among donors, 104 (30.8%) had stage IV CTE, 202 (59.8%) had dementia diagnosed by a study clinician, and 63 (18.6%) had neurodegenerative disease listed as the main cause of death.

Stage IV CTE in donors was associated with symptoms typical of dementia before death, and with a 44% higher prevalence of study clinician diagnosed dementia.

Because this retrospective observational study relied on post-mortem brain donation, causal interpretation requires caution. The researchers acknowledged several limitations, including that not all former NFL players who died during the study window were included and that some informants may have overemphasised or inaccurately recalled symptoms.

However, they said: “Together, these findings indicate that NFL players have a higher prevalence of CTE at death than has been previously shown in multiple community based studies. Furthermore, these data indicate that CTE severity at death is significantly associated with dementia in NFL player brain donors, and that dementia is common in these donors.”

Additional work is needed to further clarify the nature of this relation, particularly in other populations, with high lifetime exposure to repetitive head impacts, they conclude.

“This study provides one of the most informative estimates to date of CTE burden among former NFL players,” the researchers added.

“Above all, existing and emerging evidence on this issue must be regularly shared with past, present, and prospective NFL players, ensuring that consent to play is obtained with knowledge of the potential risks involved and the limitations of the current research evidence,” they concluded.

Thew finding  will be viewed with interest in the UK where professional rugby players have expressed concerns about the dangers of concussive head injuries and the long term effects.