This article originally appeared on Tonic.
We hear a lot about concussions in the NFL—but what about the other kind of football, the one that 265 million people around the world practice and compete in every day?
Soccer players may seem relatively safe from getting their bells rung, but a new study suggests that there's one notable exception. Researchers at the Albert Einstein College of Medicine discovered that athletes who 'head' the ball frequently are at risk for developing concussive symptoms.
In the study, published today in the journal Neurology, researchers compared intentional head impacts—heading the ball—with unintentional head impacts, such as head-to-head and head-to-goalpost hits. To do that, they had 222 adult players fill out online questionnaires for two weeks, tallying the number of impacts that occurred in both categories, as well as subsequent symptoms.
Over the two-week period, the soccer players headed the ball a median of 41 times, and nearly one in five—18 percent—reported severe concussion symptoms such as pain and a dazed state of mind. Seven percent were knocked out cold.
While the most severe symptoms were found in players who experienced the unintentional hits, the researchers also noticed a relationship between the most header-happy players and subsequent concussive symptoms.
The distinction is important because, until recently, heading the ball had been considered to be a relatively harmless aspect of the game. That way of thinking was challenged in a 2015 study published in the Journal of the American Medical Association,which set out to determine whether or not headers should be banned in adolescent soccer games. The JAMA paper concluded that even though 30 percent of youth soccer concussions are a direct result of heading the ball, the move still wasn't considered risky enough to warrant a ban.
That research, however, didn't measure the severity of the headers and focused primarily on hard hits that observers could see from the sidelines. "The key finding [of the new study] is that heading presents an independent source of symptomatic events," says lead researcher Michael Lipton.
The results are consistent with previous research that Lipton has done: He co-authored a 2013 study that found 30 percent of soccer players surveyed who headed the ball more than 1,000 times also displayed an increased risk of changes to their white matter—the connective brain tissue that controls how we learn new motor tasks.
It's important to note that the new study didn't follow up to see which players had actually suffered concussions—only concussive symptoms, which Lipton says limits the study's ability to prove the relationship.
"The takeaway," Lipton says, "is that players should be aware that the symptoms, which may be signs of concussive brain injury, are associated with high amounts of heading."
He adds that if you ever take a questionable hit—one that leads to dizziness, confusion, disorientation, nausea, or a lasting headache—do the smart thing and take a substitute.