Headers linked to memory issues, raising questions about soccer safety as the World Cup kicks off

With the Women's World Cup kicking off this week, the focus of the sports world turns to soccer -- the most popular sport in the world and one continuing to grow in the United States. However, new research is calling attention to one of the risks of the game, heading the ball, which studies find may be linked to brain problems later in life.

The newly released study, published in the journal JAMA Network Open, found that professional male soccer players who headed the ball more frequently during their career were more likely to develop memory issues. The study builds on prior studies from Scotland and France that also showed a link between playing soccer and the development of dementia.

The research was done on professional male athletes, but can guide how athletes at all levels approach the sport, Dr. Joel Salinas, an assistant professor of neurology at NYU Langone and chief medical officer of Isaac Health, an online memory clinic, told ABC News. It may be especially important for children, he says. "If you have a child, especially a child whose brain is still in the early developing phases, maybe hold off on how often you head the ball."

The new study included over 400 retired professional male soccer players that were an average of 63 years old. The athletes played soccer for an average of 14 years. Those that reported heading a soccer ball six to 15 times a game were found to have a 2.71 increased risk for memory issues, such as those seen with dementia. Players who reported heading the ball greater than 15 times a game were found to have a 3.53 increased risk of memory issues, the highest among all studied players.

The researchers said that may be because repeated headers can cause sub-concussive injuries, which are low-grade injuries that don't lead to the symptoms of a concussion but can build up over time and cause problems later in life.

"I think information like this is increasingly valuable for players and their parents," says Dr. Leah Croll, an assistant professor of neurology at the Lewis Katz School of Medicine at Temple University.

Croll says she thinks research such as this will continue to shape the rules and regulations of the game at every level.

"Some leagues have introduced policies where they restrict heading the ball for this reason, and that may be something that becomes increasingly prevalent as we learn more and more about the risk of dementia and minor traumatic brain injuries earlier in life," she says.

For example, the U.S. Soccer Federation, the governing body for soccer in the U.S., banned heading for players 10 and under in 2015.

This new study revealed that certain positions on the field had more significant risks for the development of memory issues when compared to others. Goalkeepers had the lowest risk, while defenders had the highest risk of developing memory issues. That may be because defenders head the ball more frequently than other positions on the field, the researchers said in the study.

Most research studies on headers and risk to the brain have been done on male athletes, which is a significant limitation to the data, and reflects longstanding gaps in sports medicine research around female athletes. Additionally, experts believe that female athletes face similar risks -- or maybe higher risks, according to some research -- from heading the ball. "There is some research to suggest that women might be more likely to have concussions and might have more severe symptoms from concussions, but we just don't have enough information to say anything definitive at this point," Croll says.

There's still more to learn about headers and dementia risks, including the risks to athletes who may not play soccer for as many years as the professionals. But for now, experts say athletes at all ages should learn proper heading technique and take a break from playing if they're having any concussion-like symptoms after headers, including headaches, dizziness, or confusion.

Despite the mounting evidence linking head impacts to the development of issues with the brain, Croll says there is a lot left to understand, especially around how we can help people who have already developed issues. "Looking into treatments could potentially be a very, very exciting future direction," she says.

Alexander Garcia, D.O., is an internal medicine resident at Cooper University Hospital in Camden, New Jersey, and a member of the ABC News Medical Unit.