The brain’s protective barrier remains leaky for years after playing contact sports

The brain’s protective barrier remains leaky for years after playing contact sports

By Max Kozlov & Nature magazine

For decades, scientists have struggled to understand exactly how years of taking blows to the head while playing sports can lead to severe memory loss and dementia later in life.

Now, a study published today in Science Translational Medicine reveals that the protective shield known as the blood-brain barrier can be damaged and leaking decades after an athlete retires from the sport. This persistent leakage appears to trigger a long-lasting immune response that is closely linked to cognitive decline, the study finds.

The work is a “very important study that finds the disruption of the blood-brain barrier many years after head trauma,” says Katerina Akassoglou, a neuroimmunologist at the Gladstone Institutes in San Francisco, California, who was not involved in the research.

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Long-term damage

Part of the difficulty in studying the long-term effects of head trauma is that some neurodegenerative conditions, such as chronic traumatic encephalopathy (CTE), can only be diagnosed by examining neuronal tissue after death, says Matthew Campbell, a specialist in neurovascular genetics at Trinity College Dublin, who co-authored the paper.

Campbell and his colleagues wanted to see if they could detect warning signals in live athletes by looking at the blood-brain barrier, a dense layer of cells lining the blood vessels that supply the brain. This layer usually prevents harmful substances from leaking out of the blood and into the brain tissue.

To investigate, researchers scanned the brains of 47 athletes who had retired from contact sports with a high risk of concussions and repetitive head impacts, such as rugby and boxing. They also examined a control group of non-athletes and athletes who had played non-contact sports.

The brain scans showed that the blood-brain barriers of the contact sports athletes were significantly more leaky than those of people in the control group, even though the athletes had been retired for an average of 12 years at the time of the study. People with the most extensive barrier damage performed worse than those with less extensive leakage on memory and cognitive tests, the researchers found.

“This was the first evidence in the living human brain that the blood-brain barrier is disrupted in individuals likely to have CTE,” says Campbell.

Difficult diagnosis

Standard blood tests used to detect brain damage were not very effective at identifying those experiencing cognitive decline, the researchers found. Instead, the warning signs became visible only after the team examined the athletes’ immune systems: the blood of those with the greatest barrier damage and the greatest cognitive decline contained a higher proportion of inflammatory white blood cells and other biomarkers of immune activation than the blood of those with less extensive damage. “It looked like the athletes were living systemically in a hyper-inflamed state,” says Campbell.

The discovery suggests that brain scans that detect leaky vessels may one day serve as a tool to identify living patients at high risk for serious brain diseases, the authors write. It also gives scientists a potential target for developing treatments to prevent this type of neurodegeneration.

These results should not deter people from organized physical activity, says Campbell. “Playing sports is incredibly healthy for the brain,” he says. “The kind of damage we’re seeing is from long-term exposure — it’s the cumulative nature of head trauma that’s concerning.”

The researchers then hope to replicate their findings in a larger population. Campbell says the study included few women — just seven out of 62 athletes and control participants combined — because currently there are far fewer retired elite female athletes than male athletes.

This article is reproduced with permission and var first published March 18, 2026.

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