Repeated blows to the head, for example from boxing, rapidly cause brain damage. PHOTO: ALAMY / IMAGESELECT / STEVE SKINNER
A striking number of nerve cells disappear from the brains of young athletes who sustain blows to the head.
Young athletes who receive blows to the head over many years show signs of brain damage at an early stage – even in the absence of chronic traumatic encephalopathy (CTE). This is the finding of a study published on 17 September in Nature. CTE is a brain disease that develops following repeated head injury and is characterised by accumulations of the tau protein, but can only be confirmed after death.
Abnormalities
Researchers at Boston University examined post-mortem brain tissue from 28 men under the age of 51. Most had played American football, one of the best-known contact sports. Other sports such as football, ice hockey and rugby are also associated internationally with repeated head injury. Eight of the men studied had no history of contact sport, nine were athletes with no signs of CTE, and eleven had early-stage CTE. In all athletes who had been exposed to repeated head contact over a prolonged period, the researchers found clear abnormalities.
The most striking finding was an average loss of 56 per cent of nerve cells in the superficial layers of the cerebral cortex. This affected primarily the outermost layers in the sulci of the cortex, where the mechanical forces during a blow are greatest. These neurones form connections between brain regions and play a role in cognitive function, mood and stress regulation. Their loss may contribute to the symptoms that young contact sport athletes frequently report, such as difficulties with concentration or feelings of depression. Notably, this neuronal loss appeared to be independent of the presence of tau protein.
Inflammatory profile
The researchers also observed that brain immune cells shifted from a resting state to an inflammatory profile. In certain subpopulations, genes involved in inflammatory responses and oxidative stress were active, including SPP1 and HIF1A. Small blood vessels also showed changes. An analysis of signalling pathways suggested that microglia activate vascular cells via the molecule TGFB1, which in turn contribute to tissue damage. Such interactions may form a vicious cycle in which inflammation, reduced blood flow and neuronal loss reinforce one another.
According to the authors, this confirms that it is not only concussions but, in particular, the many smaller blows that are harmful in the long term. They see opportunities for further research into biomarkers that could detect brain changes during a person’s lifetime.
Heading ban
The study appears at a time when the subject is also firmly on the agenda in the Netherlands. On 3 September, the Dutch Sports Council presented its advisory report Hoofdzaak to State Secretary Judith Tielen (VVD). It contains proposals for a ban on heading for children and a mandatory helmet requirement in high-risk sports.