"Ex-pro footballers 3 times more likely to get dementia from heading balls," reports The Sun.
The headline was prompted by a study of 7,676 male ex-professional footballers in Scotland, which found they were more likely to die from conditions linked to brain or nerve damage. These conditions, called neurodegenerative diseases, included Alzheimer's disease and other types of dementia.
The question of whether heading footballs can damage the brain has been debated for years and much of the UK media suggests it was the key reason why such a link exists.
But it's important to note:
This was a large, well-conducted study that's of concern to professional football. But research is still at an early stage and there's currently no suggestion that anyone should stop playing football.
Regular physical activity – including football – is a good way to reduce the risk of dementia and conditions such as heart disease. Find out more about ways to reduce your risk of dementia.
The researchers who carried out the study were from the University of Glasgow and Queen Elizabeth University Hospital in Scotland.
The study was funded by the Football Association and the Professional Footballers' Association, and published in the peer-reviewed New England Journal of Medicine (NEJM) on an open-access basis.
You can read the study on the NEJM website.
The study had widespread coverage in the UK media. The reports included a range of figures for the increased risk of dementia-related death among former footballers. This happened because the researchers used a variety of methods to assess the risk, and looked at different dementia-related conditions separately.
Media stories tend to choose the most alarming figures to report.
Mail Online and BBC News reported that the men had played football between 1900 and 1976. However, the study did not mention when the former footballers had been active players, it only mentioned that men born before 1 January 1977 were eligible for inclusion in the study.
This was a cohort study, carried out retrospectively (after the events had happened). These types of studies are useful for identifying links between risk factors (in this case playing professional football) and outcomes (deaths from neurodegenerative disease).
But cohort studies do not tell us what is behind the link. This means we cannot say that playing football increases the risk of neurodegenerative disease, or that heading the ball is the reason for any increased risk.
Researchers used databases of male former professional footballers from Scotland, born before 1977. They identified their community health index numbers (the Scottish equivalent of an NHS number), which enabled them to check the players' death certificates and prescription records.
Each player was matched with 3 men of similar age, living in an area with a similar level of social deprivation. These men formed the control group.
The researchers looked at the men's records from their 40th birthday until December 2016 or until they died. They recorded deaths from all causes, including deaths due to cardiovascular disease, respiratory disease, cancer and neurodegenerative conditions.
Neurodegenerative conditions included Alzheimer's disease, non-Alzheimer's dementias, motor neurone disease, Parkinson's disease and all dementias not otherwise specified.
The researchers calculated how likely footballers were to have died from any cause or from specific diseases, compared to the men in the control group. They took into account 'competing risk' – for example, the risk of dementia is higher if the risk of dying from another disease first is lower.
In addition to examining death certificates, the researchers looked into whether the men had been prescribed dementia medicines. They did this because some people with dementia do not have it recorded on their death certificate.
During an average 18 years of follow up from age 40, the researchers found 1,180 former footballers (15.4%) and 3,807 control group men (16.5%) had died. The average age at death was 67.9 years for footballers and 64.7 years for men in the control group.
Looking at the causes of death, researchers found:
After taking account of competing risks of death, researchers said the risk of having died of a neurodegenerative illness was about 3.5 times higher for professional footballers than the control group (subhazard ratio 3.45, 95% confidence interval (CI) 2.11 to 5.62).
The neurodegenerative disease with the strongest link to professional footballers was Alzheimer's disease. The study found 0.8% of former players and 0.2% of control group men died from Alzheimer's disease – a risk 5 times greater for the footballers (hazard ratio 5.07, 95% CI 2.92 to 8.82).
Former footballers were almost 5 times as likely to receive a prescription for dementia medicines than control group men (odds ratio 4.90, 95% CI 3.81 to 6.31).
There was no significant difference in risk of death from neurodegenerative disease between goalkeepers and outfield players. But goalkeepers were 59% less likely to have been prescribed dementia medicines than outfield players (odds ratio 0.41, 95% CI 0.19 to 0.89).
The researchers said: "our data show that mortality from neurodegenerative disease was higher and prescriptions of dementia-related medications were more common among former professional soccer [football] players than among controls from the Scottish population."
They warn that "these observations cannot be applied directly to recreational and amateur soccer [football] players."
The study results suggest that professional football players have a higher risk of neurodegenerative diseases, including Alzheimer's disease, than the rest of the population. But the actual risk remains low.
What the study does not tell us is why that is, or whether that risk applies to people who play football at non-professional levels.
The study is a starting point to find out more about the risks for professional players, most importantly to try to find whether there is a specific cause (such as heading the ball) and whether that risk can be reduced. Cohort studies cannot tell us what is behind a raised risk of a health condition.
Limitations of the study include the average age being 40 with 18 years of follow up which may not be long enough for an outcome such as death from dementia.
It also only looked at footballers born before 1977. It's possible the results do not directly apply to people playing football today.
There might be some as-yet undiscovered reason why footballers are more at risk of Alzheimer's disease, unconnected to heading the ball. However, repeated head trauma is linked to brain damage, so head injury in football is certainly a good place for researchers to start looking.
The study results may not apply to the majority of people who play football for fun. Even keen amateur footballers are unlikely to play as often or as intensively as professional players. Football is a good way to keep active and healthy. This study does not mean that people who enjoy kicking a ball about for fun should be worried about it.