Tackles on the rugby pitch 'increase dementia risk' claims
Playing rugby could increase the chance of dementia if players receive repeated knocks to the head, The Daily Telegraph has reported.
So should ‘egg-chasers’ – both amateur and professionals - be worried? The quick answer is probably not as The Telegraph has seriously dropped the ball when it came to reporting on this study, which actually looked at an entirely different sport - American football.
The study looked at retired American football players and found that they were at threefold risk of dying from neurodegenerative diseases than the general population. Neurodegenerative diseases are debilitating diseases where there is progressive loss of nerve cells leading to gradual loss of function.
The players were also four times more likely than the general population to have Alzheimer’s disease or a specific type of motor neurone disease recorded on their death certificate (either as a cause of death or contributing cause).
While not directly proven, the researchers argue that the increased risk is probably the result of recurrent episodes of concussion.
A significant problem with the reporting on this study is that, despite first impressions, rugby is a very different game to American football.
American football tends to be faster-paced with a greater emphasis placed on ‘blocking’ – where one player obstructs another’s path with his body. If this move is performed when the other player is running at speed, it can often result in some degree of concussion.
That said, there is some concern in rugby circles about the impact of regular concussion on the brain, with new international rules recently being introduced to reduce the risk.
Where did the story come from?
The study was carried out by researchers from the Centers for Disease Control and Prevention (CDCP), US, and was funded by the centers' National Institute for Occupational Health and Safety.
The study was published in the peer-reviewed journal Neurology.
While the main body of The Telegraph’s report was accurate its headline was very misleading.
The headline made no mention that the study was actually about American football. If you were of a cynical bent you may suspect that the term ‘rugby’ was used to draw people attentions to what is in fact a very US-centric story.
What kind of research was this?
This was a cohort study in which researchers looked at the causes of death among 3,459 retired professional National Football League (NFL) players in the US.
In particular, it analysed the causes of deaths from neurodegenerative diseases disorders and compared findings to death rates within the general US population. These are debilitating diseases where there is progressive breakdown or death of nerve cells leading to gradual loss of function; examples are Alzheimer’s and Parkinson’s disease.
The researchers point out that previous research has raised concerns about the longer-term health effects of recurrent concussion associated with American football, as well as other contact sports such as boxing, ice hockey and (proper) football.
In particular, a link has been suggested between multiple concussion and a specific form of dementia called chronic traumatic encephalopathy (CTE). CTE is a recently recognised disorder and as such it does not currently have a code in classification systems. This is used to record causes of death such as the World’s Health Organization’s International Classification of Diseases (ICD) system.
So while the researchers think that CTE played an important role in the development of neurodegenerative diseases, as a category, it was not included in this research.
What did the research involve?
The researchers identified 3,439 NFL players with at least five playing seasons between 1959 and 1988 from a pensions fund database. Details of deaths and the causes of death were ascertained from 1979 through to 2007, from the National Death Index and other official sources.
They analysed the causes of deaths among the football players, using a standardised analysis system, and including three neurodegenerative diseases:
- dementia/Alzheimer’s disease
- Parkinson’s disease
- amytrophic lateral sclerosis (ALS, which is a specific type of motor neurone disease where there is progressive damage to the nerves that supply the muscles, leading to muscle weakness and wasting, and eventually paralysis)
They compared the mortality rates from disease among American football players with standard US male mortality rates from 1960-2007.
They did two types of analysis:
- looking at when the condition was listed on death certificates as the main cause of death; or
- giving a wider inclusion by also looking at when any of these conditions were listed on death certificates as contributing causes, or serious co-existing conditions, but were not written as the direct cause of death. For example, Alzheimer's disease can make people more vulnerable to potentially fatal lung infections
In their analyses, researchers placed players into two categories depending on the position they played:
- ‘nonspeed players’ (all linemen – players who specialise in playing at the line of scrimage )
- ‘speed players’ (all other positions, with the exception of the punter/kicker, such as the quarterback or linebackers)
This was done in order to examine possible differences in risk between different positions.
What were the basic results?
There were 334 deaths among American Football League players included in the study where 62% were in ‘speed’ positions.
Compared to the general male population:
- Overall death rates among the players (any cause) was actually lower than in the general population (standardised mortality ratio, SMR, 0.53, 95% confidence interval [CI] 0.48 to 0.59) – possibly because ex-professional American football players tend to be healthier than the average man
- Players were more likely to die from a neurodegenerative disease than the general population (SMR 2.83, 95% CI 1.36 to 5.21).
- Players were more likely than the general population to have ALS (SMR 4.31, 95% CI 1.73 to 8.87) or AD (SMR 3.86, 95% CI 1.55 to 7.95) recorded on their death certificates (either as cause of death or contributing condition).
- They found a trend for higher death rates from neurodegenerative diseases among players in speed positions compared with players in non-speed positions, but this did not reach statistical significance (rate ratio 3.29, 95% CI 0.92 to 11.7).
How did the researchers interpret the results?
The researchers point out that the American Football League players were at threefold risk of dying from neurodegenerative diseases than the general population, and four times more likely to have Alzheimer’s or a specific form of motor neurone disease (ALS) listed on their death certificate. These results, they say, were consistent with recent studies that suggested an increased risk of neurodegenerative disease among American football players.
The researchers point out that it is not possible from this research to determine the cause of this increased risk. But other studies suggest that American footballers who have suffered repeated blows to the head are at increased risk of neurological disorders. And players in speed positions – who are able to build up ‘considerable momentum before being tackled by or tackling another player – experience concussions more often than non-speed players.
Though not assessed by this study, the researchers also say that chronic traumatic encephalopathy (CTE) may have been the true primary or secondary factor in some of these deaths.
Similar findings between multiple concussions and other contact sports, such as boxing and ice hockey, have been found in earlier studies.
Conclusion
As a cohort study this research cannot prove that playing professional American football caused higher rates of death from neurodegenerative diseases. Nevertheless the results are of concern.
The detailed findings on risk should be viewed with caution since the numbers of men dying from these disorders was very small. Overall, 10 of the group died from all neurodegenerative diseases (two from dementia/Alzheimer’s, six from ALS and two from Parkinson’s). Related to this, the confidence intervals around some of the risk estimates are quite wide, which means we can have less confidence that this is the true size of the risk figure.
As the authors point out, the results of the study are limited to long-term professional players (although they also say that CTE has been seen in college age and professional football players with relatively short careers).
Also the majority of the players (78%) first began playing before 1980. It could be the case that improvement to safety equipment since this time may mean that the results are not a accurate reflection of the risks faced by modern NFL players.
The study cannot show what might have contributed to the higher mortality rates from neurodegenerative diseases. Although repeated episodes of concussion are thought to be a risk factor, the study has not looked at whether players in this study had a history of concussion or not.
The findings also cannot be applied to rugby players in the UK. That said, there is some concern in rugby circles about the impact of regular concussion on the brain. New international rules have reportedly been introduced to reduce the risk.
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