Advanced CTE Strongly Linked to Dementia in Major Brain Study

A major study from the Boston University CTE Center provides evidence that advanced chronic traumatic encephalopathy (CTE) is a distinct cause of dementia. Researchers examined brains from 614 donors who were exposed to repetitive head impacts and found that stage IV CTE quadrupled a person's odds of dementia, while stage III CTE made a person twice as likely to have dementia symptoms.

The study, published January 26, 2026, in Alzheimer's & Dementia, included 366 brains with CTE and 248 without. None of the brain donors had neurodegenerative disease diagnoses other than CTE. Researchers found that people with more severe CTE (stages III and IV) had worse cognitive and functional symptoms. Those with stage IV CTE were 4.5 times more likely to have had a dementia diagnosis than those without CTE. In contrast, milder CTE (stages I and II) was not linked to dementia, cognitive symptoms, or functional symptoms.

The researchers also accounted for vascular injury, substance use, and age, and gathered information about the donors' mood, behavior, and thinking abilities. The analysis revealed that the relationship between advanced CTE and dementia is just as strong as the link between dementia and advanced Alzheimer's disease.

Head injury is common among people who play contact sports, serve in the military, or are exposed to physical violence. Repetitive head impacts can lead to CTE, a progressive brain disorder. CTE is a disease found in brain tissue that includes a build-up of an abnormal protein called tau in a pattern that looks different from Alzheimer's disease. The changes in the brain might start months, years or even decades after the last head trauma.

Currently, CTE can only be definitively confirmed by examining the brain after death. It is difficult to diagnose during life and can be misdiagnosed as other neurodegenerative diseases, such as Alzheimer's disease or other forms of dementia. Among brain donors who were diagnosed with dementia during their lives, 40% had been told they had Alzheimer's disease. But autopsies later revealed they had no signs of Alzheimer's at all and instead, CTE.

Mood and behavioral symptoms were not associated with any stage of CTE, even though these are common symptoms in people with repetitive head impacts. This suggests that these symptoms might be caused by other types of brain damage related to repetitive head impacts rather than CTE itself.

"By examining hundreds of brains and ruling out other common neurodegenerative diseases, the team could look at CTE alone and linked it to symptoms reported during life," explains the acting director of NIH's National Institute of Neurological Disorders and Stroke, which funded the research.

"Establishing that cognitive symptoms and dementia are outcomes of CTE moves us closer to being able to accurately detect and diagnose CTE during life, which is urgently needed," said study co-author Michael Alosco, an associate professor of neurology at Boston University.

The study also quiets claims from some sports-affiliated medical groups that CTE lacks clear clinical symptoms. The data showed that while low-stage CTE might not always cause noticeable impairment, the advanced stages are undeniably linked to trouble performing daily tasks like managing finances or driving.