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Tackling the potentially damaging effects of American Football head on

by on 2015/02/06

As the dust settles from last Sunday’s NFL Super Bowl, you might think that’s the end of that for another year (were you even aware it was on?). Given the over-padded nature of American football players, at least to European eyes, you could be forgiven for thinking that players are well protected against the tackles and knocks encountered. However, a rather well-timed study has suggested that professional American footballers who began playing before the age of twelve were more likely to experience memory and other cognitive impairments many decades later, compared to those who took up the sport a few years later.

What did the research say?

The researchers, led by Professor Robert Stern from The Boston University Alzheimer’s Disease Center, were interested in how head impacts sustained during sport might be associated with cognitive function in later life. Their interest wasn’t just in impacts resulting in concussion, but that “subconcussive head impacts” might also be detrimental.

The study, published in the journal Neurology, is actually quite straightforward to describe. Professional footballers had been enrolled in a larger study on the development of chronic traumatic encephalopathy, a progressive, degenerative disease resulting from repeated head injury. The participants were all male, aged between 40 and 69, and had all played professional football for at least two years (though with at least 12 years of football experience). They were split into two groups depending on whether they began playing football before or after they were 12 years old. The researchers decided on the cut-off as critical developmental changes occur in the brain between the ages of 10 and 12, but little is known about the effect of repeated head impacts during that time. Of 72 eligible participants, 42 were retained to ensure the groups were matched for age.

All participants completed three neuropsychological tests: one of executive function, which assesses things like the ability to plan or inhibit inappropriate responses; another testing memory; and one where the ability to pronounce irregular words is used an indicator of a person’s maximal cognitive ability. The results of the study were quite clear: after accounting for the length of time playing football and education, those who started playing before the age of 12 performed worse on all the tests. The researchers concluded that sustaining repeated head impacts during key stages in brain development increased the risk of cognitive impairment in later life.

The researchers were careful to note a number of limitations. Firstly, the sample was small (only 42 individuals, and all male), and all had been professional football players. It therefore wasn’t clear if the deficits reported would also be seen in people who stopped playing football after high school or college, for example, or with other sports. The researchers also noted that if those who started playing football earlier were lower in ability to begin with, that might partly account for the differences seen in later life rather than there being a direct detrimental effect.

What did the media say?

As you might expect, the study received coverage across a range of North American outlets, with less coverage elsewhere. However, the Daily Mail led with “Should under 12s be BANNED from playing football? New study claims risk of damage to young brains is too great”, which many would be forgiven for misinterpreting as referring to football, rather than American football. That aside, the coverage was actually very clear, and included detailed quotes from two of the study authors. The reference to the researchers suggesting under 12s be banned does not appear in the study though, and appears stronger than the quotes from the researchers who stress more research is needed.

The most important caveat, and one that the researchers stress in the study, was that age of first exposure was a proxy measure for the number of head impacts. It was presumed that playing for longer will have resulted in more impacts, but they did not have a direct measure of the latter. The Daily Mail coverage does usefully include details gleaned from the study press release, with additional indications that those starting before the age of 12 might have performed about 20% worse on the cognitive measures.

The bottom line.

When we consider factors that affect our health in later life, there’s a whole lifetime of experiences that determine how we age. Studying this can be difficult, and often involves the use of imperfect methods of assessing distant exposures. While earlier exposure to football appeared to be damaging, the researchers were careful to highlight replication with larger, more diverse samples would be needed before clear recommendations could be made. As the Daily Mail concludes quoting the researchers, sporting participation has so many benefits that any potentially damaging aspects must be identified so they can be made safer.

Stamm, J. M. et al. (2015). Age of first exposure to football and later-life cognitive impairment in former NFL players. Neurology. DOI: 10.1212/WNL.0000000000001358

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