When compared to the bone-jarring crash between two football helmets, heading a soccer ball might seem almost innocuous. But those seemingly mild hits to a soccer player's head may damage the brain at a deep, molecular level, according to a new study.
"It's entirely possible that the innumerable subconcussive hits that those players have may really be a culprit (for brain injury) as well," said Dr. Michael Lipton, associate director of the Gruss Magnetic Resonance Research Center at the Albert Einstein College of Medicine in New York and the study's lead author.
The theory gaining ground among many concussion experts is that the unfortunately-named 'subconcussive' hits - less-forceful hits that don't cause an overt concussion - when they accumulate over time, may prove to be more damaging than their more flamboyant cousins.
That means seemingly subtle hits - jostling the brain by bouncing a ball off of it - when they happen over and over again, could be just as bad as a more jarring hit.
"Long-term damage may have less to do with the number of diagnosed concussions and perhaps more do to with the number of subconcussive impacts to the head," said Kevin Guskiewicz, the chair of Exercise and Sport Science at the University of North Carolina at Chapel Hill, who was not involved in the study.
Lipton and colleagues studied 37 young, healthy, amateur soccer players who headed the ball between as few as 32 and as many as 5,400 times during the preceding 10-month season.
Players filled out a questionnaire to gauge the number of times they headed the ball the previous year; they also underwent tests of their attention and memory, and had their brains scanned.
The scans revealed an association between heading and damage to white matter (brain tissue that helps to convey signals across brain regions), but with a caveat.
In similar studies of subconcussive impact, the association tends to be: The more hits to the head, the more damage to the brain. Basically, "...the more you head the ball, the worse cognition gets," said Lipton. "But we found that's not the case."
In Lipton's study, published Tuesday in the journal Radiology, players had to reach a certain number of headers before the brain scan reflected damage. After that threshold was reached, brain function dropped precipitously.
It took between 900 and 1,500 headers for abnormalities to be discernible on brain scans. But the first obvious indication of a problem outside the brain occurred around 1,800 headers, when players in the small sample had measurable problems with memory tests.
The suggestion is that the brain's intrinsic ability to repair itself works, to a point. After that point, however, the brain cannot keep pace and becomes overwhelmed.
"That tells us that pathological change happens at a lower level than clinical manifestation of problems," said Lipton.
In short, there is a tipping point - and that point is different for everyone.
We are years away from knowing whether - like pitching limits to protect young baseball players' elbows and shoulders - we are on the cusp of heading limits for soccer players.
And in this study, Guskiewicz points out that we do not know how the players' previous history of subconcussive hits may have affected the outcome of their brain scans in this study.
"This one study should not place a cloud over the sport of soccer," said Guskiewicz. "This is an interesting finding, but there is much more to be learned about this."
And the usual caveats apply to this small study: A larger study group will give more nuance and clarity to the still-murky issue of long-term damage conferred by subconcussive hits.
Lipton and his colleagues are in the midst of recruiting hundreds of soccer players for that study, to take an even closer look at heading, brain changes, even the role of genetics.
"We are absolutely not making any recommendations that people should lock to some specific threshold (for heading)," said Lipton. "We don't know yet."