Could getting hit on the head during sport cause brain disease later?

A new take on research from the past five years means that the rules of sport may be about to change — and could see players spending more time off the field.

In June, the Concussion in Sports Group (CISG), a network of head injury experts who set the standard for how these injuries are treated in sports, said for the first time that repeatedly getting knocked on the head may be “potentially associated” with someone developing an untreatable brain disease called chronic traumatic encephalopathy (CTE). 

CTE, which can only be diagnosed after death, causes memory loss, changes in personality, and violent behaviour, and has been found mostly in people with a history of head injuries.

In the past, experts also looked at whether there could be a link between playing contact sports and the chance of someone developing other types of brain diseases, such as dementia, Parkinson’s or amyotrophic lateral sclerosis (ALS).

With ALS, the nerves that control how the body’s muscles move start to die, and as with CTE worsens over time. Former South African rugby player Joost van der Westhuizen died of this condition in 2017.

Head injuries in sports have been big news lately. A group of former rugby players — amateur and professional — said their brain damage is because of injuries from playing and are suing World Rugby for not making the rules safer. Former New Zealand player Carl Hayman, 41, who has been diagnosed with early-onset dementia and probable CTE, is part of the lawsuit.

The group’s move marks an about-turn since their last statement in 2017 in which they said there isn’t enough evidence to prove the disease is caused by frequent hits to the head. The panel of experts maintain in their newest statement, though, that this connection cannot be confirmed despite public health agencies saying that CTE is caused “in part” by head blows.

The new document also says that if someone is suspected of having suffered a concussion, they should be examined more thoroughly immediately during the match — which could change the rules of play in some sports.

Need for a timeout

The group advises that a 10 to 15-minute check-up should be done away from the field if a concussion is suspected, said Jon Patricios, a sports medicine physician and one of the authors of the consensus statement, at a press briefing last month. If medics think it’s not safe to go back to play, they will have to sit out the rest of the game. 

Though the rules of professional rugby  allow for players to leave the field to be checked for a concussion, the CISG’s new recommendations could mean that a rule change for soccer is on the cards. 

In this game, play must start again after about three minutes of interruption. If a concussion check longer than this has to be done — as the CISG recommends — a player will have to leave the pitch and their team will have to carry on with one less pair of legs. If they can’t return, the game will have to finish with another player in their place. 

Having to make a decision in three minutes or taking time to do an off-field assessment while the team is one player down could put pressure on medics to rush an appraisal — and potentially miss a symptom of a serious injury.

The International Football Association Board, which makes the laws for soccer, decided in January 2021 to trial a permanent concussion substitute rule. This would allow a team to replace a player suspected of having a concussion without using up one of the three normal subs which they often use at tactical moments in a game — but the catch is that the player can’t return to the game.

Players want a temporary concussion substitute rule instead. This means that if they’ve had a hard hit on the head, they’d be able to be checked thoroughly — in a quiet area such as a changeroom, away from prying eyes. If the medics clear them, they can go back to the game.

After the CISG’s statement, professional soccer players worldwide again asked for this to be considered, saying it will “protect [their] health and wellbeing”. 

But in January, soccer’s rule-making board rejected the idea of temporary concussion substitutes because, they said, it would increase the chance of misdiagnosis and a player returning to the field, which could make their injury worse. Moreover, they said, “team doctors do not see concussion events very often and cannot be expected to perform a full head-injury assessment at speed”.

Previous research, new understanding

The CISG’s statement is based on 10 systematic reviews done since the last in 2017. In a systematic review, researchers look at the findings of many studies on the same topic and draw out patterns that hold across all of them. This is why this type of analysis is seen as one of the most reliable forms of evidence in health research. 

In one of the reviews, the authors identified 14,813 studies that mentioned whether concussions and repeated head injuries in sports affect athletes’ brain health later in life. They included only 28 in the end, because the studies had to be of the case — control or cohort type. 

In such study designs researchers look at the chance of a condition, such as a brain disease, developing in people who are exposed to a certain factor (the “cases”) compared with those who aren’t (the “controls”) or they track a group with the same characteristics or experiences — such as playing contact sport and called a cohort — over time.

To understand whether there could be a link between brain disease and repeated head injuries, the factor being investigated was having often received a blow to the head. “Cases” were former athletes — professional or amateur — and the “controls” were people who did not play sports.

The conclusions showed that former professional athletes may have a bigger chance of getting diseases that destroy the nerves that control muscle function later in life, but not amateur-level players. 

Yet a prominent study on head impacts and CTE published last year by a group of researchers led by Chris Nowinski, a neuroscientist and co-founder of the Concussion Legacy Foundation, a US non-profit involved in research on concussions and CTE, was not included.

Why was the Nowinski study not considered?

The study didn’t meet their review conditions, says the CISG. Nowinski and his colleagues did a narrative review, which describes the general context around a research topic from published studies but without choosing them in a systematic way. Though Nowinski and his colleagues looked at six case-control studies, they were not designed to measure the risk of the disease as the CISG was specifically interested in so they couldn’t be included.

But the CISG says they still need better evidence, including cohort studies, before they can say for sure that repeated head blows cause CTE. Such studies would need to account for factors such as someone’s level of education, genetics and general health and lifestyle factors such as smoking, high blood pressure or heart disease, which research has shown can affect whether someone develops a brain disease, says Robert Cantu, a co-author of the statement and a professor of neurosurgery at Boston University. 

To prove that hard hits to the head cause brain diseases, researchers would also need to know how bad these knocks must be and how many someone must have had, the statement says.

In a study published in the journal Nature Communications in June, scientists examined the brains of 631 former American football players that had been donated to research after their death. 

By using data about the force with which a helmet is hit in different player positions in this sport and how long someone played during their life, the researchers could create a model to predict whether an athlete could develop CTE. 

The results showed that the more hits to the head someone receives, the worse the brain damage — and that with each extra year someone played, the chance of developing the brain disease rose by 15%.

The CISG says sports in which head injuries are not examined properly should think about making “rule changes in the interest of player welfare”.

This story was produced by the Bhekisisa Centre for Health Journalism. Sign up for the newsletter.

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