Heading a soccer ball repeatedly could be bad for the brain, according to a growing body of research about the potential long-term impacts on brains and minds from frequent collisions between heads and balls.
Much of this research is suggestive, rather than definitive. But with the women's World Cup building toward its crescendo, and many young people gathering their cleats and kits for the start of fall soccer seasons, the issues of whether heading is safe - and how to make it safer - has rarely seemed more urgent.
A study published in JAMA Network Open in March, for instance, found collegiate male soccer players developed a lingering imbalance in the levels of tau proteins in their bloodstreams immediately after practising headers.
This kind of imbalance could "indicate emerging pathological processes" inside the players' skulls, said Peter Filipcik, a professor with the Institute of Neuroimmunology at the Slovak Academy of Sciences in Slovakia, who oversaw the new study.
In another study, published in July, also in JAMA Network Open, retired professional players in Britain who'd reported heading the ball more than five times on average per game or practice during their careers were far more likely to be experiencing cognitive decline later in life than players who'd headed less often.
"The evidence is mounting" that frequent heading "is associated with increased risk" of eventual problems with thinking and memory and possibly dementia, said Weiya Zhand, a professor of epidemiology at the University of Nottingham, and senior author of the study.
Like a car ramming a wall
Unfamiliar with heading? It's a showy, signature soccer play in which someone redirects a speeding ball with his or her head.
The impacts can be substantial. In a 2022 study of female college players, scientists measured the G-force, a gauge of linear acceleration, during heading, using sensors in players' mouthpieces.
"Astronauts during rocket launch may experience a few g's of acceleration," said Lyndia Wu, an assistant professor of mechanical engineering at the University of British Columbia who led the study. "A car traveling at 35 mph running into a wall could experience about 30g of acceleration."
In Wu's study, heading often resulted in impacts of 22g or more, with some of the impacts surpassing 30g.
Heading also led to high rotational velocity or forces whipping the head sideways, she and her colleagues found.
What heading does to the brain
Unsurprisingly, these forces can have disagreeable effects on the brain.
"The rapid movement of the skull during heading produces motion between the brain and the skull and stretching of brain tissue," said Tanner Filben, a graduate research associate and doctoral candidate in biomedical engineering at Wake Forest University, who, like Wu, has used specialized mouthpieces to track the forces generated during heading.
While these impacts rarely result in concussions, Wu said, they "can still cause movement and twisting and turning of brain tissue inside the skull. Brain material is very soft and wobbly," she continued, "similar to the consistency of Jell-O" and stretches, deforms, and jiggles like gelatin when subjected to sudden knocks.
Does such deformation cause brain injury? The question remains unsettled, but recent findings are rattling researchers. In a study last year from Norway, scientists tracked the levels and types of microRNAs, which are specialized molecules involved in gene activity, in the bloodstreams of professional soccer players after they'd practiced heading.
The researchers found that some mRNAs believed to contribute to brain inflammation increased for several hours after heading. Neuroinflammation can contribute to the development of dementia and other degenerative brain conditions, said Stian Bahr Sandmo, a professor at the Norwegian School of Sport Sciences in Oslo, physician, and lead author of the study.
Strong links between soccer and dementia
On a larger scale, epidemiological studies published in the past several years show strong links between soccer and dementia, especially at high levels of play. A landmark 2021 study of almost 8,000 former professional male players in Scotland found they were, on average, about four times more likely to have developed a neurodegenerative condition, such as dementia, than other Scots. The risks were lowest for goalkeepers, who, as a group, rarely head the ball, and highest for defenders, who head the ball the most of any position, the authors wrote.
In a similar study published this year in Lancet Public Health, Swedish men who'd played in the highest division of the Swedish soccer leagues were disproportionately prone to develop Alzheimer's disease and other dementias, compared to average Swedes - except for goalkeepers, whose risks mirrored those of the population at large.
(Some male soccer players have developed either suspected or posthumously diagnosed chronic traumatic encephalopathy, a severe degenerative disease associated with multiple concussions and other brain injuries, but studies haven't yet linked heading and CTE.)
Putting limits on heading the ball
So, what should players, parents, coaches, trainers, or anyone else involved with soccer feel and do about heading?
"Head less!" said Weiya Zhang, co-author of the study of retired British players.
The United States Soccer Federation bans heading for youth players younger than 11 and limits heading among players aged 11 and 12 to no more than 15 to 20 headers a week during practices, with no limits during games.
Researchers who study heading generally would advise even greater caution, and extended restrictions. "Avoid heading before and during puberty," said Peter Filipcik, whose study looked at changes in tau after heading.
Don't devote entire practices to heading, he continued, and "do not underestimate any headache." Players should leave the game if they feel ill or injured as a result of heading.
"We found that heading of the ball increases the level of molecular biomarkers previously associated exclusively with neurodegeneration and traumatic brain injury," he pointed out.
United Soccer Coaches, a group that provides education and advocacy for soccer coaches at all levels, from youth to elite players, offers members a free online course about how to teach and refine heading technique, said Tanner Filben.
But much remains to be learned about heading, said Stian Sandmo, who led the study of mRNA changes. "We still don't know all that much about the specific neurological risks from playing soccer."
Is there, he and other researchers wonder, a "safe" amount? Is heading four times during a match or practice benign but five times too much? Are the risks different for male and female players, or for recreational athletes versus elites?
Many researchers are focusing on heading, with more and larger studies expected soon.
But right now, Sandmo said, we shouldn't let concerns about heading sour our response to the beautiful game. "The studies evaluating long-term brain health also demonstrated that soccer players lived longer with lower mortality from, for instance, heart disease," he said.
So, revel in the athleticism of the Fifa Women's World Cup players and of your own young wingers and strikers, if you're a soccer parent.
Washington Post