Longer football careers linked to reduced white matter brain integrity, study finds

Have you ever wondered how playing football affects the brain in the long run? A study from the Boston University Chronic Traumatic Encephalopathy (CTE) Center has shed new light on this question, revealing that long careers in American football are linked to changes in the brain’s white matter. These changes are associated with cognitive and behavioral issues later in life, independent of the presence of CTE, a condition often highlighted in discussions about the risks of contact sports.

The findings were published in Brain Communications.

The motivation behind this comprehensive study was the growing concern about the long-term impacts of repetitive head impacts experienced by football players. Previous research has established a connection between these impacts and symptomatic concussions, as well as the development of CTE, a progressive brain condition.

However, there was a gap in understanding how repetitive head impacts affects the brain’s white matter, crucial for cognitive function and behavioral regulation. This study aimed to bridge that gap by investigating the relationship between football career length, the age at which players start playing tackle football, and changes in the brain’s white matter.

To conduct this study, researchers analyzed brain tissue from 205 male former American football players who had donated their brains to the Veterans Affairs-Boston University-Concussion Legacy Foundation Brain Bank. These individuals had played football at various levels, from youth leagues to professional.

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The study focused on measuring levels of myelin-associated glycoprotein and proteolipid protein 1 in frontal cortex tissue. These proteins are essential for the structure and function of myelin, the protective sheath around nerve fibers that speeds up electrical signals between brain cells.

Lower levels of these proteins indicate compromised white matter integrity. White matter is composed of nerve fibers that connect different parts of the brain, facilitating communication between them. The integrity of white matter is vital for cognitive functions and behavioral regulation.

The researchers also collected retrospective information on the players’ athletic and medical histories and conducted interviews with family members to gather data on cognitive and behavioral symptoms.

The duration of a player’s career played a critical role in brain health, as more years spent playing football were associated with lower levels of proteolipid protein 1. This finding points to a dose-response relationship between the length of exposure to repetitive head impacts and the integrity of the brain’s white matter. Surprisingly, this association was not observed with myelin-associated glycoprotein levels, indicating that different components of the myelin sheath might be differently affected by repetitive head impacts.

“Damage to the white matter may help explain why football players appear more likely to develop cognitive and behavioral problems later in life, even in the absence of CTE,” said corresponding author Thor Stein, a neuropathologist at VA Boston Healthcare System and assistant professor of pathology and laboratory medicine at Boston University Chobanian & Avedisian School of Medicine.

Another significant aspect of the study was the impact of the age at which players first began to play tackle football. Starting at a younger age was associated with lower levels of proteolipid protein 1, suggesting that early exposure to head impacts could interfere with normal white matter development.

This is particularly concerning given that myelination, the process of forming myelin sheaths around nerve fibers, continues into early adulthood. Therefore, repetitive head impacts during critical periods of brain development could have long-lasting implications for brain health.

Among the older brain donors studied, decreased levels of myelin-associated proteins were correlated with greater reported functional and impulse control difficulties, underscoring the potential role of myelin degeneration in the cognitive and behavioral symptoms observed in individuals exposed to repetitive head impacts. This connection between decreased white matter integrity and clinical symptoms emphasizes the broader impacts of football on brain health, extending beyond the risk of developing CTE.

“These results suggest that existing tests that measure white matter injury during life, including imaging and blood tests, may help to clarify potential causes of changes in behavior and cognition in former contact sport athletes. We can also use these tests to better understand how repeated hits to the head from football and other sports lead to long term injury to the white matter,” said co-author Michael L. Alosco, an associate professor of neurology.

However, the study is not without its limitations. The sample consisted of brain donors who were symptomatic and had decided to donate their brains for research, which may not represent the broader population of former football players. Additionally, the focus on myelin-associated glycoprotein and proteolipid protein 1 measurements in the frontal cortex means that the findings may not apply to other brain regions. Future research will need to include a more diverse group of participants and explore other areas of the brain to fully understand the impact of repetitive head impacts.

“More years of football play and younger age of first exposure to football were associated with decreased myelin proteins,” the researchers concluded. “… Myelin degeneration is another potential pathological consequence of [repetitive head impacts] that might contribute to the manifestation of clinical symptoms. Further characterization of the pathologies that arise from [repetitive head impacts], including those of the white matter, and their relative contribution to objectively defined clinical and cognitive symptoms will inform future iterations of the traumatic encephalopathy syndrome research diagnostic criteria, as well as treatment and preventative targets in this vulnerable population.”

The study, “Decreased myelin proteins in brain donors exposed to football-related repetitive head impacts“, was authored by Michael L. Alosco, Monica Ly, Sydney Mosaheb, Nicole Saltiel, Madeline Uretsky, Yorghos Tripodis, Brett Martin, Joseph Palmisano, Lisa Delano-Wood, Mark W. Bondi, Gaoyuan Meng, Weiming Xia, Sarah Daley, Lee E. Goldstein, Douglas I. Katz, Brigid Dwyer, Daniel H. Daneshvar, Christopher Nowinski, Robert C. Cantu, Neil W. Kowall, Robert A. Stern, Victor E. Alvarez, Jesse Mez, Bertrand Russell Huber, and Ann C. McKee, and Thor D. Stein.