Worsening cognitive function in football players stems mainly from frequent ball heading rather than unintentional head impacts due to collisions, researchers have warned.
The findings suggest that efforts to reduce long-term brain injuries may be focusing too narrowly on preventing accidental head collisions.
"Unintentional head impacts are generally considered the most common cause of diagnosed concussions in soccer, so it's understandable that current prevention efforts aim at minimising those collisions," said lead author Michael Lipton, Professor at the Albert Einstein College of Medicine in New York, US.
"But intentional head impacts -- that is, soccer ball heading -- are not benign. We showed in a previous study that frequent heading is an underappreciated cause of concussion symptoms. And now we've found that heading appears to alter cognitive function as well, at least temporarily," Lipton added.
For the study, published in the journal Frontiers in Neurology, researchers recruited 380 amateur football players in New York City. They filled out questionnaires detailing their recent (previous two weeks) on-field activity, including heading and unintentional head impacts.
Participants also completed neuropsychological tests of verbal learning, verbal memory, psychomotor speed, attention and working memory. The players ranged in age from 18 to 55, and 78 per cent were male.
Players headed balls an average of 45 times during the two weeks covered by the questionnaire. During that time, about one-third of the players suffered at least one unintentional head impact -- kicks to the head or head-to head, head-to-ground, or head-to-goalpost collisions.
Players who reported the most headings had the poorest performance on psychomotor speed and attention tasks, which are areas of functioning known to be affected by brain injury.
Heading frequency also correlated with poorer performance on the working memory task. In contrast, unintentional head impacts were not related to any aspect of cognitive performance.
"Heading is a potential cause of brain injury and since it's under control of the player, its consequences can be prevented," Lipton noted.