Two studies published on Wednesday raise concerns about the consequences of repeated minor head impacts in athletes. The findings suggest that damage to the brain can occur well before, or independent of, a diagnosis of chronic traumatic encephalopathy, or C.T.E.
The first study, written up in the journal Nature, focused primarily on amateur (and a few professional) football players, all of whom died by 50. When scientists examined tissue from the brains of these 20 men, they found that some of their brains had signs of the tau tangles that are indicative of C.T.E. and others did not. But all of them showed significant damage to multiple different types of cells. The research sheds light on the changes that can occur in the brain leading up to the development of C.T.E.
What’s more, while some of the athletes had a history of a traumatic brain injury, or T.B.I., some did not. Instead, the scientists think the changes in their brains were largely caused by multiple small hits to the head.
“You think about American football, two guys on each side of the line running into each other during a play,” said Jonathan Cherry, an assistant professor of pathology and laboratory medicine at the Boston University Chobanian & Avedisian School of Medicine, who led the research. “That’s not considered a T.B.I., so to speak, because it happens hundreds of times a game, but it’s still really debilitating.”
The study found that, on average, the men had a 56 percent loss of a specific type of neuron in the frontal cortex, the region most affected by C.T.E. There was also damage to the brains’ blood vessels and changes to immune cells that triggered inflammation. These findings were not present in a control group that also died young but did not play contact sports.
“I think a lot of people believe C.T.E. is black or white, you have it or you don’t have it,” Dr. Cherry said. “We think it’s more of a spectrum.”
Studying the early phases of C.T.E. is important because it can help identify what the triggers are that cause the tau tangles to form, said Dr. John Crary, a professor of pathology at the Icahn School of Medicine at Mount Sinai, who was not involved in the research. “And if you understand what the trigger is, then you can target it.”
The second study, published in the journal Neurology, used M.R.I. scans to observe the brains of 352 (living) amateur soccer players, most of whom were in their 20s. The researchers looked specifically at where gray matter (the body of a neuron) intersects with white matter (the long axons that project out of the cell body) — an area thought to be particularly vulnerable to head impacts. The more frequently a player headed the ball, the more damage they had, and the worse they performed on cognitive tests.
Dr. Michael Lipton, a professor of radiology at Columbia University Irving Medical Center, who led the research, made clear that despite their lower scores, none of the young adults met a clinical threshold for impairment. “It’s more of a question as to whether this could have implications for the future,” he said.
In both studies, the greatest damage occurred in the frontal cortex, a region important for planning, working memory and decision making. And it was centralized in the sulci — the grooves in the brain — where scientists believe cells are especially susceptible to harm. Think of the sulci as the serrated edges on a ketchup packet, Dr. Lipton explained. It’s much easier to tear something at those jagged points because that’s where the force gets concentrated.
The most important potential impact of the two papers is identifying possible early warning signs of C.T.E., said Dr. Lea Grinberg, a professor of neuroscience and laboratory medicine and pathology at the Mayo Clinic. The hope would be to one day “develop a test that we can detect in living people using these markers,” she said. (Dr. Grinberg was not part of either study.)
While these findings are worrisome, scientists stressed that the research represents a relatively small pool of athletes. All of the football players died young, many by suicide or from accidents or illnesses, and their brains were donated for research.
That suggests there is “bias in the referral sources to the brain bank,” with only more severe cases represented, Dr. Crary said.
And the damage seen in the soccer players was in those who head the ball thousands of times per year, not in people who do it closer to a hundred times. “You have to be in the upper 25 percent or so before we start to see these subclinical changes in brain imaging and cognition,” Dr. Lipton said. “I don’t think there’s enough evidence to say that heading is absolutely bad.”
None of the experts called for an end to contact sports. But they do hope the research can help people mitigate their risk.
“When we talk about risk factors, the greatest one for C.T.E. is years of playing a sport, years of exposure,” Dr. Cherry said. If children start playing football a little later in life, or stop playing a little earlier, or play flag football instead of tackle, that can offer some protection, he added.
Dana G. Smith is a Times reporter covering personal health, particularly aging and brain health.
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