Wednesday June 12 2013
Over a quarter of a billion people play football regularly
"Headers can damage a footballer's brain, study finds," is the worrying warning in The Daily Telegraph. Football is one of the world's biggest participation sports, so it's important to know if it has any adverse health consequences. Fortunately for budding Rooneys and Ronaldos, the risks of heading balls may have been hyped in the headlines.
The news is based on a US study that tested whether regular "heading" of a football led to brain changes that could indicate traumatic brain injury, a type of injury usually only seen after a severe blow to the head.
Researchers gave 37 amateur players advanced brain scans that can detect changes in the brain's white matter. They also carried out neurological tests and asked players how often they thought they headed the ball.
The researchers found that more heading was associated with changes similar to those seen in people who suffered traumatic brain injury. Heading was also associated with poorer memory scores.
Despite these results, there is no evidence of a direct casual link between headers and brain damage. The people in the study were only tested at one point in time, so it is uncertain if the current findings represent any new changes, or if the players already had poor memories or abnormal white matter.
Any potential risk of brain injury has to be balanced against the wide range of health benefits from playing football regularly.
Where did the story come from?
The study was carried out by researchers from Albert Einstein College of Medicine of Yeshiva University, US. The US National Institutes of Health and the US National Institute of Neurological Disorders and Stroke funded the study, which was published in the peer-reviewed online edition of the science journal Radiology.
In general, the media headlines that suggest that heading a football can leave you with traumatic brain injury and memory loss are rather alarmist, and do not take account of the important limitations of this small cross-sectional study.
A number of papers highlighted the case of West Bromwich Albion legend Jeff Astle, who died at the age of 59 from a degenerative brain disease. A coroner attributed this disease to many years of heading footballs. However, as the Daily Mirror rightly points out, footballs were much heavier during Astle's playing career (1959-77) than they are now.
What kind of research was this?
This was a cross-sectional study examining the association between football heading and evidence of brain changes that indicate traumatic brain injury.
The researchers say they chose to study footballers as football is one of the most popular sports worldwide and it is unclear whether repetitive heading of the ball causes permanent damage.
This type of research can only indicate possible associations between lifestyle factors (such as heading footballs) and health outcomes (such as brain changes). However, it cannot establish cause and effect.
To reliably assess the effects, researchers would need to regularly image players' brains – with the first assessments ideally before they started playing football – and follow them up over time to see how any changes are related to objective assessments of the number of headers the players had made.
However, for several reasons – including cost (MRI scans are expensive to carry out) – a prospective cohort study is unlikely to be feasible.
What did the research involve?
Thirty-seven football players (28 men and nine women; median age 31 years) were recruited from amateur football leagues in New York City. The players completed a questionnaire that asked them to estimate the amount of footballs they had headed in the previous 12 months. This was so the researchers could rank them into "exposure" groups in order to compare levels of exposure and any related abnormal brain changes. They categorised exposure as:
- low exposure (≤276 headings per year) – nine people
- medium exposure (277-1,095 headings per year) – 19 people
- high exposure (≥1,096 heading per year) – nine people
The questionnaire also asked whether the players had experienced one or more concussions in their lifetime. To determine this, participants were asked a series of questions about any previous head trauma for which they had tried to receive, had received, or were recommended to receive medical attention.
Each player underwent neurological tests supervised by a neuropsychologist to test their:
- psychomotor speed (a measurement of the relationship between brain function and physical movement)
- executive function (such as planning)
Finally, the players underwent a brain imaging technique called diffusion tensor imaging (DTI). DTI is a specialised type of MRI scan that the researchers used to detect any abnormal changes to the structure of the brain, including evidence of any prior trauma (such as signs of small bleeds).
DTI assesses the movement of water molecules with and along the nerve fibres that make up the brain's white matter. The researchers say the DTI imaging technique allowed them to measure the "uniformity of water movement (called fractional anisotropy, or FA) throughout the brain". They say abnormally low FA within white matter has previously been associated with cognitive impairment in people with traumatic brain injury.
Associations between heading and abnormal brain changes were then determined using statistical analyses.
What were the basic results?
The participants reported having played football for an average of 22 years and an average of 10 months during the previous 12 months.
In total, they reported heading a football between 32 and 5,400 times (median 432 times) in the previous 12 months.
The main findings of the research were:
- there were no signs of structural abnormality or bleeds identified among any of the participants
- greater heading exposure was associated with significantly lower fractional anisotropy (FA) at three regions in the brain diffusion tensor imaging – the threshold for the amount of headings and an association depended on the region of the brain the changes were seen in (range of heading thresholds was 885-1,550)
- there was a significant association between heading exposure and memory function, with an association threshold of 1,800 headings per year identified
- there was no association between heading exposure and neurological tests, other than memory
- reported concussions over the participants' lifetime and other demographic details were not significantly associated with either brain matter changes or neurological performance
The researchers say these findings are consistent with findings from another study of people with traumatic brain injury.
How did the researchers interpret the results?
The researchers conclude that heading a football is associated with abnormal changes to the white matter (nerve fibres) of the brain, as well as poorer neurocognitive performance. They say this relationship is not explained by a history of reported concussion.
Discussing the study's findings, lead researcher Dr Michael Lipton said: "Our study provides compelling preliminary evidence that brain changes resembling mild traumatic brain injury are associated with frequently heading a soccer ball [football] over many years."
Overall, this research provides no evidence that there is a direct cause and effect between repeated heading of a football and traumatic brain injury. However, there are several important limitations to this study that are worth noting.
One-off tests and scans of players
The people in the study only had brain images and neurological tests at one point in time, and were asked about heading in the previous year and if they had any concussions in their lifetime.
Without having the imaging and neurological tests prior to the year in question – or preferably in early periods of life, before they started playing football – we don't know whether the current findings represent any new changes.
It could be that the white matter always looked the way it did on imaging, or has done so for a long period of time. As such, the study does not prove that one causes the other – there may have been other factors at play not identified in this research that caused the brain changes seen.
Small study sample size
This was a very small study, with only 37 amateur football players participating. Larger prospective studies involving repeat brain imaging and neurological tests from a much larger number of people from more than one area are needed to draw further associations. It would also be interesting to test professional footballers, who are likely to head the ball more but use a better technique.
Amount of heading was self-reported
Heading was determined by self-reporting, and it is possible participants did not accurately report how often they headed the ball in the previous 12 months. This can make the results less reliable. In the rush and confusion of a football match, are players really going to accurately remember how many times they have headed a ball?
Lack of information on heading
The research did not take into account different types of headers, considering the speed, velocity and site of impact. These are all important factors when looking at the repetitive nature of heading.
Real-world outcomes for players
We don't know whether the observed brain structure and memory test performance actually had a significant impact on the person in terms of their everyday life and functioning.
Overall, it is plausible that repeated minor impacts to the head may be associated with changes to the brain similar to those seen in people with traumatic brain injury. However, on its own this small study does not provide proof that heading a ball directly causes brain injury.
On a more positive note, we know regular exercise (such as playing football) can help lower blood pressure and cholesterol levels, which in turn can reduce the risk of heart disease and stroke. These benefits have to be weighed against any theoretical risk of memory problems caused by frequently heading a ball.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.