Class actions over links between concussion and brain injuries have made big headlines in the US.

Law firms are planning concussion class actions in Australia against the NRL or its clubs. A class action involving former AFL players is being prepared.

Professor Chris Levi, co-director of Hunter New England Health's Sports Concussion Clinic, warns that fears about concussion are getting ahead of the science.

"We're increasingly concerned that the public is being fed information that is unbalanced and at times misleading," Professor Levi, a neurologist, said.

"There's been calls from researchers to ban contact sport and comments made that allowing children to play contact sport is the equivalent of child abuse," he said.

Fears about concussion should not be used to stop people playing sport, he said.

"Football, soccer, netball, baseball, cricket - they're all potentially contact sports. The benefits of participation in terms of physical activity are enormous," he said.

Professor Levi said many stories appearing in the media linking concussion to health problems were anecdotal and "not evidence".

"Correlation and causation are quite different."

Former Knights star Andrew Johns recently said doctors had raised possible links between his epilepsy diagnosis and concussion.

"[The doctors] can't be sure what caused it. It could be something that popped up later in life. But they think maybe - and that's maybe - a contributor could be some of the concussions I've had, some of the continual head knocks," Johns said in March.

Dr Mark Cook, head of neurology at St Vincent's Hospital in East Melbourne, said recently that large studies of people with traumatic brain injuries show an increased risk of epilepsy.

"Even through mild brain injuries, the risk is at least doubled," he said.

University of Newcastle clinical neuropsychologist Andrew Gardner has, for the past seven years, conducted concussion research that involved assessments of more than 100 retired players, including numerous former Newcastle Knights.

Dr Gardner, co-director of Hunter New England Health's Sports Concussion Clinic, said the research included cognitive assessments and brain MRIs.

Those assessed range in age from 40s to 80s.

"We're just starting to get some of those former players to come back for a second time to see if there are any differences in their performance across those two timeframes," he said.

As well as concussion, the research is examining a spectrum of potential disorders, diseases and variables that may influence ageing.

This includes chronic pain, arthritis, anxiety, depression, sleep quality and sleep apnoea, along with drug and alcohol use.

All of these issues can affect cognitive abilities.

"Things like high cholesterol, diabetes, high and low blood pressure, having a previous history of smoking, how much alcohol you're consuming, the sleep you're getting, if you have sleep apnoea - that's a huge impact on your cognitive skills," Dr Gardner said.

Mental health also affects cognition.

"Anxiety and depression are not that uncommon in the general population.

"If there are lots of people who have anxiety [for example] and lots have had concussions, there will be an overlap. But there's no proven cause and effect. It's just a strong association."

Dr Gardner was concerned that retired players see concussion stories in the media and then believe it's a huge problem "when we don't have the science to back it up".

He said this could lead some to link memory lapses, like forgetting their keys and wallet, to fears about concussion and chronic traumatic encephalopathy [CTE].

Some may falsely assume they have CTE or dementia, placing an unnecessary strain on their mental health. CTE, which affects memory, thinking and mood, can only be diagnosed by autopsy.

In 2016, Jeff Miller, a senior official with America's NFL, publicly acknowledged a connection between gridiron and degenerative brain disorders like CTE.

The comment came after years of the NFL disputing such links. It also came about a year after the NFL settled a class action involving thousands of former players. The agreement provides up to $5 million per retired player for serious medical conditions associated with repeated head trauma. Claims have surpassed US$600 million.

In July, it was reported that an autopsy on former Canterbury player and coach Steve Folkes showed he had CTE. Folkes died of a heart irregularity last year at the age of 59.

In an SBS Insight program on concussion last week, Bulldogs legend Steve Mortimer said his memory wasn't what it used to be.

He sometimes forgets names and what he needs at the supermarket unless he writes a list.

"Since I've retired and probably when I entered into [my] 60s I started forgetting things. That was never me," Mortimer said.

Former Parramatta legend Ray Price told the program that he, too, forgets things.

"I'm 66 years old. Gee, if I'm not allowed to start forgetting things now, when do I start?"

Mr Price would forget where he put his keys, "you know, little trivial things".

"Not what my name is or what my wife's name is."

His mother died of dementia and his family was worried that he had the disease.

Lawyers say about 100 former players have joined the AFL class action, including 50-year-old Shaun Smith.

Mr Smith suffers from depression, sleep apnoea and anger issues. He believes concussions sustained in his AFL career are the reasons for his health problems.

Professor Levi said it was important that research was done to "refine the knowledge" of concussion, so we "actually know what the long-term issues are".

"We don't know at the moment. And there's a lot of bias in the research from some quarters," he said.

Dr Gardner said years of research were needed.

"We're not saying there's no problem at all. There are issues. We just don't know what the cause of those are and how much concussion is contributing to it," he said.

"We're saying let's not jump to huge conclusions while we don't know the answers. Let's do the research and find out."

None of this detracts from the necessity for sporting codes to properly manage concussion incidents.

Professor Levi, who gives independent advice to NRL club doctors on a pro bono basis, said the focus should be on "minimising the occurrence of concussion through regulation of games".

Concussion required proper management through "recognition and care", so players were "not exposed repeatedly or excessively".

Dr Gardner, a concussion consultant for Rugby Australia, said: "If somebody is concussed or looks concussed, they should be removed from playing and not returned until they're feeling better".

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