Former All Blacks doctor John Mayhew says more studies need to be done to determine a direct link between concussions and the risk of dementia, but it's a potential problem rugby bodies must be aware of.
In the wake of ex-All Black Carl Hayman's early-onset dementia and probable chronic traumatic encephalopathy (CTE) diagnosis at the age of 41, Mayhew told Newstalk ZB's Kerre McIvor that people shouldn't jump to conclusions about the causes.
"Obviously, we don't know the cause of his dementia and just because he's a prominent ex-All Black and played rugby, there's not always a definite cause or link between the two," Mayhew said.
"But it's certainly very sad news and certainly rugby is aware of the risks of head injury and the chronic effects. We still don't know if it's a direct link between several concussions and the risk of dementia in later life, so it's unfounded.
"But certainly, in this case, it needs to be taken seriously and unfortunately chronic traumatic encephalopathy is usually a diagnosis made post-mortem, which obviously we don't want that to be the case here."
Hayman played 45 tests for the All Blacks between 2001-07, during which time he was considered the best tighthead prop in the game, before becoming one of the world's highest paid players when he joined Newcastle and Toulon, winning three European titles with the latter French team.
As Hayman revealed to Dylan Cleaver's The Bounce, however, the close to 450 professional games he played took an irreversible toll on his brain, and Hayman has joined a landmark suit being prepared on behalf of 150 former professional rugby players, claiming rugby's governing bodies, including World Rugby, failed to protect players from the risks caused by concussions and sub-concussions, despite being armed with the knowledge and evidence to do so.
Mayhew said that while rugby had "to be aware there's a potential problem and follow the evidence-based medicine approach to it" there could be other contributing factors to early onset dementia such as alcohol and drug use.
"We still don't know, directly, the link between recurrent head injuries and the subsequent brain damage," Mayhew said.
"It is very, very young to have dementia – if that's what he's got. Some of the other cases I've been involved with in the past, the diagnosis hasn't been dementia and so we need to be aware that there can be other factors – alcohol, drugs and things like that – and there are some conditions which cause pre-senile dementia, so to speak.
"We need to be aware of that. Each case has to be analysed on its merits, and it's hard to look back on someone's career and say 'well, what dose of head injury did you have to cause this? Did you have enough, or was it just the result of one blow, or multiple blows?'"
Former All Blacks doctor John Mayhew. (Photo / Photosport)
In recent times, rugby has made changes to lower the risk of head injuries, particularly with rules around the tackle and the breakdown. Players are now also taken from the field to be assessed for concussion if they suffer a knock to the head, and can return to a doctor rules them fit to continue.
"It's a concern, but the right things are being done," Mayhew said. "I think we've got to make sure that we don't scare people away from our national game and unnecessarily. Most head injuries that we see in hospital and things like that are not related to rugby; they're due to car accidents or other types of trauma.
"That macho attitude has gone away and you see today the guys come off which what seem relatively trivial injuries and they're assessed properly by independent doctors and taken off the field, and I think the players accept that, the coaching staff accept that and even in rugby league, there's been a dramatic shift there.
"I think the management going forward of head injury is much better, especially in the professional game. It's a little hard in the amateur game, the club game, the third-grade game where there's no one on the side line keeping an eye on the players so there's an educational process that needs to go on there, but in professional contact sport – certainly in New Zealand – we're doing a much better job at managing head injuries.
"But as people point out, it may be that one head injury is enough to end someone's career and we've seen examples of that. Whereas other people can have 20 head injuries and make a full recovery. There's a lot of unknowns and I think we have to be careful that just because we have a famous ex-player who has a medical problem that it's related to their rugby playing. It may be totally unrelated to that."
Studies on brain injuries in sport
There have been several studies on the effect of head injuries on athletes in high impact sports like rugby and American football.
A study by the University of South Wales on a professional rugby team claims that players saw a decline in both blood flow to the brain and cognitive function after just one season, reports the BBC.
Boston neuropathologist Ann McKee, who is known for her work studying Alzheimer's disease and the consequences of repetitive traumatic brain injury, found evidence of CTE in 110 out of 111 brains belonging to former NFL players.
While there have been questions about selection bias with McKee's study, given families most likely to donate the brains of their loved ones are those who had concerns there was something wrong, McKee still pointed to the unusually high number of CTEs in the brains studied.
"Even with the bias, you don't see this number of CTEs in a brain bank for Alzheimer's disease," McKee told the Herald in 2019. "It's very rare; it's 2-5 per cent. Then you have a brain bank for football players and it's 99 per cent. Even statistically, the evidence is quite strong.
"If you're collecting for dementia, it's an uncommon cause, broadly, in the general population of men and women, including people who've never played sports. Then you look at football players, it's a very high percentage. Even the college athletes are at 91 per cent in that study."
In 2019, Dr Chris Nowinski, the co-founder of the Concussion Legacy Foundation, told the Herald it is only a matter of time before CTE is discovered in the brain of a New Zealand rugby player.
Meanwhile, fifty former elite rugby players, including England's Ben Kay and Wales' Shane Williams, are being recruited to a study into whether they are more likely to show early warning signs of dementia.