On Jul. 11, 2025, findings from Northwestern University study show the brain protein tied to CTE is not elevated in former amateur football players. In recent years, some scientists and advocates have warned that playing contact sports like football and hockey may increase the risk of brain diseases like Alzheimer’s or chronic traumatic encephalopathy (CTE) due to a buildup of a specific protein in the brain. But a new Northwestern Medicine study of 174 donated brains, including some from former high school and college football players, pumps the brakes on that theory.

The finding raises important questions about how scientists interpret subtle brain changes associated with aging, Alzheimer’s disease and repetitive head impacts. The study, published in the Journal of Alzheimer’s Disease, examined brain tissue from the Lieber Institute for Brain Development, which collects brain donations from people who had psychiatric conditions — schizophrenia, major depression, general anxiety, substance use disorder, etc. — throughout their life.

Of the 174 samples collected from older adult men (with a median age of 65 at death), 48 men participated in football in high school or college while 126 had no history of playing a contact or collision sport. The study did not include brains from professional athletes.

The scientists focused on a small memory-related brain region called CA2, part of the hippocampus. This region has been shown to accumulate phosphorylated tau (p-tau) protein — which is often present in neurodegenerative disease — in a variety of contexts, including normal aging, Alzheimer’s disease and in individuals with a history of repetitive head impacts.

Interestingly, the findings suggest p-tau buildup in CA2 isn’t specific to contact sports. The scientists found no over-representation of CA2 p-tau in individuals with a history of youth football participation. Instead, the presence of p-tau in this region was statistically associated with age.

The study also highlights broader challenges in the field of neurodegeneration research. In particular, the authors point to the difficulty of assigning clinical meaning to subtle pathological findings, underscoring how even expert consensus groups struggle to define CTE in clinically meaningful terms.

The authors call for larger studies to better understand how p-tau relates to aging and head injuries, while urging the scientific community to critically evaluate assumptions about what constitutes neurodegenerative disease.