Soccer players who frequently head the ball may be increasing their risk for concussion, a new study reports.

The study, published Wednesday in Neurology, included 222 amateur soccer players — 175 men and 47 women — who reported the number of times they headed the ball over a two-week period. The athletes also reported any unintentional head impacts, such as collisions with other players or the goal post.

Over the two-week period, men had head contact with the ball an average of 44 times, while women headed the ball an average of 27 times. Overall, players reported heading the ball an average of 5.3 times a game. Players who headed the ball the most (those in the top quartile of heading reports) were three times as likely to have concussion symptoms, such as pain, dizziness and feeling dazed, compared to those players in the lowest quartile.

Collisions with another player or the goal post were far more risky. Those with two or more unintentional head collisions were six times as likely to have concussion symptoms as those who reported a single impact. In 470 reports of head impacts, a fifth resulted in moderate or severe symptoms of concussion.