Jasmin Fox-Skeli
BBC, freelancer
If you're a soccer player, there's no greater thrill than when you jump towards a ball coming at you at high speed, head it and send it into the net, scoring a goal for your team.
And yet there is growing evidence that constant headbanging leads to brain damage that manifests decades later as Alzheimer's or Parkinson's disease and motor neurone disease.
The dangers of contact sports have been known for almost 100 years.
In 1928, American pathologist Harrison Martland published a scientific article in which he claimed that, "for some time now, fight fans and promoters have acknowledged that a peculiar condition occurs among trophy boxers when they speak, in ring parlance, of 'blow-shock stupor'."
Symptoms included a staggering gait and mental confusion, and were most common in "slow fighters, who are usually poor boxers and take a significant amount of punishment to the head."
In some cases, the intoxication from the blow would progress to dementia, later classified as "dementia pugilistica" – a type of dementia that occurs in boxers who have suffered a large number of head injuries.
At first, it was thought that the problem was limited to the world of boxing.
But in recent decades, that attitude has changed.
West Bromwich Albion and England footballer Jeff Astle died in 2002 at the age of 59 after being diagnosed with early-onset dementia.
In America during this time, American football player Mike Webster died suddenly at the age of 50 from cognitive decline and other symptoms similar to Parkinson's disease.
In both cases, brain scans of these sports stars showed that they died of chronic traumatic encephalopathy (CTE) – a more modern term that has replaced the diagnosis of dementia pugilistica.
There were other notable cases.
Former Chicago Bears player David Duerson died by suicide on February 17, 2011, after suffering from depression.
Subsequent analysis of his brain showed that he also had CTE.
"CTE is a really specific form of degenerative brain pathology, because we only see it in people with a history of head injuries or blows to the head," says Willie Stewart, a neuropathologist at the University of Glasgow, UK.
This condition is also recognizable because if you look under a microscope, you will see a specific pattern of abnormal deposition of a protein called tau in the brain.
“The best way to determine if someone might have CTE is to ask them ‘have you ever played football?’ or ‘have you ever played rugby?’ Because if you are a professional football player and you have dementia, then the chances of you having CTE in your brain are very high,” says Stewart.
Since 2008, Anne McKee, a professor of neurology and pathology at Boston University School of Medicine, has been inviting former athletes to participate in research studies to learn how to diagnose and treat CTE.
In 2023, McKee and her colleagues analyzed the donated brains of 376 former US National Football League (NFL) players and found that a staggering 91,7 percent of them had CTE.
The contingent featured former Philadelphia Eagles quarterback Rick Arrington, who played for the team between 1970 and 1973, and former Kansas City Chiefs defensive end Ed Lothamer, who played in the first Super Bowl.
This does not represent a true risk of getting CTE among American football players, as people who suspect they might have the condition may be more inclined to donate their brains for scientific purposes.
- Can we change how our brain ages? These scientists claim that it is possible
- Five ways to recognize the symptoms of Alzheimer's
- Parkinson's disease: "You don't die from it, but you die with it"
However, for context, the prevalence of CTE among the general population is less than 1 percent.
Mackie has also diagnosed CTE in former baseball players, cyclists, and ice hockey stars.
In all cases, the common denominator was repeated blows to the head.
However, this is not just about CTE.
Heading the ball has also been linked to other degenerative brain conditions.
As part of the ongoing Impact of Football on Lifelong Health and Dementia Risk (Field) study, which he has been leading since 2019, Stewart and his team examined the health records of nearly 8.000 former Scottish professional footballers and compared them with 23.000 members of the general population.
"We took our football players and compared them to people in the community who were born the same year, and lived in roughly the same areas," says Stewart.
"We had three matched controls for each football player, so we had a good idea of what normal health and aging should look like."
The study found that former professional football players are more than five times more likely to develop Alzheimer's disease; four times more likely to suffer from motor neurone disease; and twice as likely to develop Parkinson's disease, compared to people of the same age in the general population.
Overall, former professional football players were 3,5 times more likely to die from a neurodegenerative disease than expected.
"The risk is greatest in the playing positions where we've seen the most heading," says Stewart.
"So defenders are at much higher risk than forwards, and if you're a goalkeeper, you're at about the same risk as anyone else in the general population."
Stewart's research also showed that the longer a person plays professional football, the greater the risk, ranging from about a double risk in those with the shortest careers, to about a fivefold increase in those with the longest careers.
Former international rugby union players are also at higher risk of neurodegenerative diseases.
- Are top athletes healthy people?
- Could viruses contain a cure for Alzheimer's disease?
- A French village where everyone has dementia
So what is it about heading a ball that is so harmful to the brain?
CTE tends to be diagnosed only after death, as it leaves telltale knots of an abnormal protein called tau in the cerebral cortex of sufferers.
However, Michael Lipton, a professor of radiology at Columbia University Irving Medical Center (CUIMC), used magnetic resonance imaging (MRI) to scan the brains of young amateur football players to find early signs of the condition.
“We recruited people who were over 18 and who played in some kind of organized group – so it could be a university team, but more often it was a recreational league,” says Lipton.
"We have a lot of people who don't head the ball at all and some who head the ball thousands of times a year."
His research showed that players who head the ball more often not only perform worse on learning and memory tests, but also show clear signs of damage in the part of the brain just behind the forehead – an area known as the orbitofrontal cortex.
“It’s the part of your brain that’s just above your eye sockets,” Lipton says.
The outer layer of the orbitofrontal cortex, which is made up of white matter, appears to be particularly vulnerable.
“White matter is like a network that covers the human brain, made up of very fine filaments called axons that transmit information,” says Lipton.
These fine filaments are very vulnerable to rapid acceleration caused by a sudden force.
The sudden change in head velocity during an impact causes the brain to ricochet inside the skull, stretching axons and disrupting their connectivity.
"If you think about heading, just hitting the ball is relatively mild - it doesn't cause a skull fracture or brain bleeding or any obvious injury, but what it does has the potential to transmit force throughout the brain," Lipton says.
"That force forces the brain inside the skull to move away from the point of impact."
"And the brain is extremely soft – almost the consistency of gelatin – and so when the brain takes a hit like this, it will compress, twist and deform, and that puts a lot of strain on the axons."
Subsequent research by Lipton and colleagues showed that it is the gap between white and gray matter in the orbitofrontal cortex that suffers the most damage from head-butting.
The most frequent headers, who reported heading the ball more than 1.000 times a year, had significantly more damage in that brain area.
This is probably because the gray and white matter have different densities and move at different speeds when the ball is hit.
This creates a net force between the two tissue types.
We, however, do not know what happens after that.
"Our research shows that in these relatively young, healthy people, something is happening in the brain, but it's not causing the disease at that point," Lipton says.
Some of these individuals could develop conditions such as CTE, Alzheimer's disease, Parkinson's disease, or motor neuron disease.
But many of them don't.
Just as it depends on the number of times a person heads a ball in their lifetime, it is also possible that some people are more vulnerable than others due to a combination of genetics and lifestyle factors.
In those who develop neurodegenerative disease, one hypothesis is that repeated blows to the brain may damage their blood vessels, or trigger a process of chronic inflammation that ultimately leads to the disease.
“In response to damage to the fibers and blood vessels, the brain’s healing response [inflammation] occurs to try to repair it,” says Stewart.
"It's possible that the blood vessels don't heal properly, so they're chronically leaky and letting things that shouldn't be getting to the brain. Or it could be that the healing inflammation never turns off as it should, and you end up with a chronic inflammatory process."
Or it's possible that damage to neurons causes them to fail and die, causing more and more problems over time.
"It's probably a mix of all of these that leads to long-term problems, but that's what we're trying to tease apart," says Stewart.
So what can we do to protect athletes and amateur sports players from dementia later in life?
Technology could be helpful here.
For example, researchers at Stanford University in California are designing American football helmets with built-in liquid shock absorbers, which reportedly reduce head impacts by about 30 percent.
Reducing heading could also play a role.
In the UK, as a result of Stuart's research, heading was eliminated from youth football.
His group also launched a successful campaign to reduce the amount of heading that takes place in training sessions during the week.
"What we found when we talked to football players was that they headed the ball maybe 70.000 times during their careers. But only a few thousand of those were during matches."
"That's 68.000 headers a week that no one pays attention to, so let's get rid of as many of them as we can."
However, as always, prevention is the best medicine.
"If we just stopped banging our heads against things, then that risk would go down to zero, but in practical terms, it's hard to convince people to do that," says Stewart.
Follow us on Facebook, Twitter, Instagram, YouTube i Viber. If you have a topic suggestion for us, please contact bbcnasrpskom@bbc.co.uk
- Smart watches could detect Parkinson's disease at an early stage
- Parkinson's disease: New research may reveal early causes
- 'I watched brain surgery to see if it was possible to cure Alzheimer's disease'
Bonus video:
