Playing more football doesn’t increase teenagers’ risk of brain damage, according to a new study. But critics of the sport are not impressed.

Playing American football does not harm teenagers’ brains, even if they suffer concussions—so say researchers from the Tulane Institute of Sports Medicine.

Tracking 1,289 Louisiana high school football players from 1997 to 2000, they found that the more time the teenagers spent on the field, the better they did on tests of their mental abilities.

The finding contradicts earlier reports of brain damage in football players at all levels of the sport. “The concussive forces may not be quite as bad as we think,” said Gregory W. Stewart, chief of physical medicine and rehabilitation at Tulane University School of Medicine.

The Tulane researchers presented their findings today at a meeting of the American Academy of Orthopaedic Surgeons in New Orleans.

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The study adds fuel to a controversy over the safety of American football. In recent years, physicians have been diagnosing some professional football players with chronic traumatic encephalopathy, a kind of long-term brain damage.

The worry has led to recent rule changes aimed at reducing the likelihood of head and neck injuries at all levels of the sport.

To get an idea of the risk faced by young football players, Stewart and his colleagues checked records to see how many of the boys were diagnosed with concussions—a head injury serious enough to cause symptoms such as dizziness, confusion, headache, blurred vision, and double vision.

They also had the players take a digit-symbol substitution test, which tests memory and mental processing. The researchers used other tests to check the players’ reaction times.

Four percent of the boys suffered a concussion over the time the data was collected. And all of them returned to school within 7 days.

Stewart acknowledged that some players want to stay in the game so much that they don’t admit their symptoms. But even if players were getting concussions and not admitting it, the concussions didn’t seem to affect the players’ brains.

The longer the teenagers played, the better they performed on the memory test, even when researchers controlled for the players’ ages.

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The researchers also found no association between years of football participation and reaction time.

That came as good news to Matthew J. Matava, president of the National Football League (NFL) Physicians Society. “I’m glad to see the results of the study,” he said. But he emphasized that more research is needed.

Another expert on brain injuries in sports flatly rejected the Tulane researchers’ findings. Robert Cantu, a clinical professor of neurosurgery at Boston University said that the tests in the study are out of date.

“They are not as sensitive as a lot of tests being employed today,” he said. In his own research he used diffusion tensor imaging (DTI) to scan the brains of 10 athletes who played contact sports such as football.

In a study published in World Neurosurgery in 2013, Cantu reported that the scans showed changes in the brains of the contact sport athletes at the end of the season. The brains of a group of 13 athletes who played non-contact sports did not change.

In a separate study, published in the British Journal of Sports Medicine, researchers kept track of 13 high school football players, measuring how often and how hard they got hit in the head. They put the players through a different test of mental abilities, the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT). Those who were hit more and harder showed warning signs of concussion.

ImPACT is a more accurate test, said Cantu. “Clearly in our experience there has been a correlation between the length of time an individual has been exposed to head trauma and the chance of developing brain injury.”

So what can teenagers and their parents do with these contradictory findings?

“I think this tells us that if we do the right thing with regard to taking care of players, we should be okay,” Dr. Stewart said.

That means watching for symptoms of concussion. Players with such symptoms should be taken out of the game until they can be evaluated by a physician, he said.

“There is a lot of education that needs to go on,” he said, adding that players, along with their parents, coaches, and physicians, need to be more careful.

Matava said the NFL is already working to catch concussions with tests like ImPACT on the sidelines.

Cantu would go further. He said that football players should do exercises to strengthen their necks. The worst damage occurs when the player’s head snaps or twists, he said, and stronger necks can hold heads steadier.

He would also like to see tighter rules and better enforcement from coaches, to prevent players from intentionally hitting each other with their heads. And no one should play tackle football under the age of 14, he said.

Of course you could avoid football altogether. But some of the same risks apply to hockey, soccer, and many other sports, according to Cantu.

The bottom line, according to all three experts, is to keep playing, but to also take good precautions.