In a finding that suggests football used to be a less dangerous sport, a small study shows that men who played in high school in the 1950s and 1960s may not be at increased risk for dementia or memory problems.
Risk of neurodegenerative disease
Nor did they show increased rates of Parkinson's disease or amyotrophic lateral sclerosis (ALS), commonly known as Lou Gehrig's disease.
Read: Amyotrophic lateral sclerosis (ALS)
The study used a small group of men, the researchers acknowledged. But, they added, the results are in line with an earlier study that examined men who'd played high school football in the 1940s and 1950s.
"What we can say is, for that era, football did not increase the risks of neurodegenerative disease compared with other sports," said senior researcher Dr Rodolfo Savica, a neurologist at the Mayo Clinic in Rochester, Minnesota.
That might sound surprising, given evidence that former professional football players can face increased risks of degenerative brain diseases. Autopsies have confirmed cases of chronic traumatic encephalopathy (CTE) in numerous former National Football League players.
CTE is a progressive brain disease thought to result from repeated head trauma.
But Savica said that pro and college football is "completely different" from the high school level – in intensity, size and speed of the players, and the number of "hits" they take.
Research "clearly attests" to the risk of CTE in at least some former pro and college football players, Savica said.
What's more, he added, the new findings don't prove that high school football carries no long-term risks.
Kenneth Podell, director of the Houston Methodist Concussion Centre agreed.
"It's encouraging that they [the study authors] didn't see any increased risks, but the findings should be considered preliminary," said Podell, who was not involved in the research.
Because the study is small, he said, it may have lacked the statistical "power" to detect differences between former football players and other former athletes.
Savica stressed that no one should assume the findings apply to men who played high school football in more recent years.
Read: Football makes you shorter
"That was a different era," he said, referring to the time period his team studied.
High school players have gotten bigger and faster, Savica said, and there may be more "drive to win at all costs" these days compared with decades ago.
Awareness of concussion
And while there have been advances in protective equipment, he added, that might give some players a "false sense of security" that causes them to be more aggressive, he said.
"You can still get a concussion when you're wearing a helmet," Savica said.
Podell agreed that the study findings can't be extrapolated to younger generations of high school players.
But he also pointed to some things that have changed for the better – particularly in the last decade or so.
Awareness of concussion and its shorter-term dangers has risen, and management of the condition has changed greatly since the era covered in the new study, Podell said.
Read: Concussion effects last for years
US states, for example, now have "return to play" laws that typically require players to be immediately removed from the game if a concussion is suspected. And guidelines say that athletes should not return to play until they have a doctor's approval.
Back in the era that Savica's team studied, blows to the head were typically brushed off as "getting your bell rung".
"Maybe the coach would say, 'How many fingers am I holding up?' And if you said 'two,' you'd go back in the game," Savica said.
Some big questions remain
The findings, published online in Mayo Clinic Proceedings, are based on medical records of 296 men who'd played football at one of two Minnesota high schools, and 190 who'd been involved in swimming, basketball and wrestling. All athletes played from 1956 to 1970.
Over time, the researchers found, seven former football players had been diagnosed with dementia or mild cognitive impairment. That compared with five men who'd played other sports – with no difference in the two groups' overall rates.
Similarly, three men in each group had been diagnosed with Parkinson's disease, while no one had an ALS diagnosis.
Read: Treating dementia
Some big questions remain, Podell said. One is this: Are there certain people at greater risk of lasting damage from sports-related concussions or repeated knocks to the head?
"That's something researchers are trying to understand," he said. "Are there genetic and environmental risk factors that make some people more vulnerable?"
For now, Savica suggested that parents remember that sports – including football – can benefit kids. But they should also guard against the risks, he added.
That, he said, includes knowing the symptoms of concussion, and being sure that the trainers and coaches on the sidelines know how to respond to a possible concussion.
According to the US Centres for Disease Control and Prevention, some common concussion symptoms include headache, dizziness, nausea, vision problems, fatigue and confusion.
Head impacts damage American footballers' brains
Common cause of ALS found