Soccer players who repeatedly strike the ball with their heads may be causing measurable damage to their brains, even if they never suffer a concussion, according to a study published Tuesday by the Journal of the American Medical Assn.
By examining brain scans of a dozen professional soccer players from Germany, researchers found a pattern of damage that strongly resembled that of patients with mild traumatic brain injury, said Dr. Inga Katharina Koerte, a neuroradiologist at Boston's Brigham and Women's Hospital, who led the study.
Koerte and her colleagues focused on the athletes' white matter, the interior portion of the brain that carries signals from nerve cells to the spinal cord. They tracked the movement of individual water molecules within the brain tissue to see whether the atoms moved in a narrow linear pattern or in a random, diffuse pattern. Movement along a narrow track suggested the molecules were being hemmed in by healthy fibers. Diffusion, however, suggested that brain tissue had suffered some form of damage and could no longer restrict the movement of water molecules.
Using a high-resolution MRI technique called diffusion tensor imaging, the researchers observed microscopic changes in the frontal, temporal and occipital lobes — regions that control attention, visual processing, higher thinking and memory.
The research team also scanned the brains of 11 professional swimmers, who served as controls. Their brains showed much less damage.
"The origin of these results is not clear," said senior study author Martha Shenton, a neuroscience researcher at the VA Boston Healthcare System. Although frequent "heading" of the ball may be to blame, other factors — such as falling to the ground or hitting goal posts or crashing into other players — could play a role as well, she said.
According to the U.S. Consumer Product Safety Commission, which maintains a national database of injuries, 40% of soccer concussions are the result of collisions between players, while roughly 13% are because of players heading the ball.
Though the study is small and preliminary, it is likely to fuel an already heated debate. While the danger of concussion among football has been widely studied, only recently have researchers begun to examine the risks faced by soccer players.
Statistics offered by the American Assn. of Neurological Surgeons suggest that soccer players, particularly young ones, are much less likely to suffer concussions than other athletes. In 2009, soccer players under the age of 15 suffered 8,392 concussions, according to the group. In contrast, bicyclists in that age group suffered 40,272 concussions; football players, 21,878; and baseball and softball players, 18,246.
However, the JAMA study focused on "sub-concussive" injuries, impacts that were not strong enough to cause a concussion. In selecting their soccer-player subjects, researchers included only men who had never reported suffering a concussion and had never been diagnosed with one by a physician.
None of the abnormalities seen in the study were apparent on conventional MRIs. Diffusion tensor imaging is revealing previously unobservable brain injuries, but it's unclear whether the white matter changes seen in this study would cause any problems, said Dr. Robert Harbaugh, director of the Penn State Institute of the Neurosciences, who was not involved in the study.
"It's way too early to make that next step and say, 'Well, if we see this, we should really worry about people playing soccer because they're going to get dementia at age 50,'" Harbaugh said. "I don't think we've got anything like that kind of information."
At the American Youth Soccer Organization, which oversees some 900 soccer groups nationwide, safety officials said head injuries and concussions were the hottest topic of late.
Karen Mihara, director of AYSO's Safe Haven program, said the organization had adopted recommendations put forth by the Centers for Disease Control and Prevention to deal with head injuries. Players, parents, coaches and officials must get instructions on how to identify concussion symptoms. When signs of concussion are recognized, players must be removed from play for the day and parents are urged to take their child to a physician for treatment. Players must obtain a medical release before being allowed to play again.
AYSO has also experimented with special helmets for heading, but they did not provide added protection, Mihara said.
"What we've found in some cases is the opposite effect, especially with younger children," she said. "They feel they're protected and play with reckless abandon more than they might if they didn't have it."