A study of men who graduated from Wisconsin high schools 60 years ago found those who played for their school's football team were no worse off neurologically than those who didn't play the sport.

The results add to the ongoing debate over the safety of contact sports in adolescence, but the study's senior author said the findings may not apply to today's high school athletes.

"The big caution is that these findings may not generalize to high school football today, because the game has changed a lot," said Dylan Small, of the Wharton School at the University of Pennsylvania in Philadelphia. "The players are generally bigger and youth sports have become much more professionalized."

Earlier research has found higher rates of a brain condition known as chronic traumatic encephalopathy (CTE), other brain ailments and mental health issues later in life among former professional football players, the researchers write in JAMA Neurology.

Not much is known about how concussions and hits to the head among U.S. high school football players might be linked with these outcomes, though.

For the new study, the researchers used data from 3,904 men who graduated Wisconsin high schools in 1957. The men were enrolled in the study during their senior year and then monitored throughout their lives.

The researchers had data measuring brain and mental health for 2,692 of the men at age 65.

To test cognition, the men were first asked to recall words and then to say all the words they know starting with specific letters. They were evaluated for depression using a standard scale.

Overall, at age 65, cognition and depression scores were no worse among the former football players than among the men who never played the sport during high school.

Scores were similar when the men were tested again at age 72 years.

"What our study is kind of saying is that the dose of football in the 1950s for the average player didn’t carry big risk, but we don’t know what that says about the current risk," Small told Reuters Health.

Also, he said, the findings only address the average risk for all the former players who participated. The study can't show whether some men are at an increased for cognition problems and depression if they played a certain position or suffered concussions.

Dr. Kristine Yaffe, of the University of California, San Francisco, agreed that the study can't say people who suffer multiple concussions aren't going to experience problems later in life.

"It does say - on average - participation in football doesn't carry deleterious cognitive outcomes later in life," said Yaffee, who co-authored an editorial accompanying the new study.

She said more studies that follow people who suffer hits to the head are needed to see how they fare, but those are difficult to conduct. Some are in the works, though.

Small said his team is hoping to examine a similar set of data collected from people who graduated high school in the 1970s to get information on more recent exposures.

Yaffe said research on effects of brain injuries on health in later life is still evolving.

"This is a new field and there is a lot we don’t know about it," she said. "It’s prudent to be careful, but we also don’t want to jump to conclusions. So this study is somewhat reassuring."